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| author | Brian Paul <brian.paul@tungstengraphics.com> | 2003-01-09 18:24:46 +0000 |
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| committer | Brian Paul <brian.paul@tungstengraphics.com> | 2003-01-09 18:24:46 +0000 |
| commit | 8b4a34dcdbd89e74e87ecb8bb1cb8c0a7b11b093 (patch) | |
| tree | e1a2ad6917e2e7997031768d4f6cf2e3c4f03957 /docs | |
| parent | 267bc32309ce381a0c48df6a965d4dc601be61c3 (diff) | |
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diff --git a/docs/subset.html b/docs/subset.html new file mode 100644 index 0000000000..46e437c64e --- /dev/null +++ b/docs/subset.html @@ -0,0 +1,3644 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <title>Mini GLX Specification</title> +</head> +<body> +<span style="font-style: italic;"></span><span + style="font-weight: bold;"></span> +<h1> +<center>OpenGL Subset Specification</center> +</h1> +<h2> +<center> +<h3>(preliminary - Jan 9, 2003)</h3> +<h3>Tungsten Graphics, Inc.</h3> +</center> +</h2> +<p><span style="font-style: italic;">[This is an incomplete, +preliminary document. All information is subject to change. Please +see Appendix A for a list of open issues.]<br> +</span><br> +</p> +<p> This document describes a subset of OpenGL implemented by Tungsten +Graphics, Inc. for embedded devices. Prior to reading this +document the reader should be familiar with the OpenGL 1.2.1 +specification dated April 1, 1999 (available from <a + href="http://www.opengl.org/developers/documentation/specs.html">http://www.opengl.org/developers/documentation/specs.html</a>.) + Experience with OpenGL programming is highly advisable.<a + href="http://www.opengl.org/developers/documentation/specs.html"><br> +<br> +</a></p> +<h1>1. Introduction</h1> +To summarize, the following major features of OpenGL are omitted from +the subset:<br> +<ul> + <li>Vertex arrays</li> + <li>Texture coordinate generation</li> + <li>Lighting</li> + <li>Point size</li> + <li>Polygon stipple</li> + <li>DrawPixels, CopyPixels, PixelZoom</li> + <li>1-D and 3-D textures</li> + <li>CopyTexImage</li> + <li>Fog</li> + <li>Depth test</li> + <li>Color Index mode</li> + <li>Accumulation buffer</li> + <li>Feedback mode</li> + <li>Evaluators</li> + <li>Push/Pop attributes</li> +</ul> +<p>Further reductions are made at a lower level of detail.<br> +</p> +<p>As in the OpenGL specification, OpenGL identifiers are printed in <span + style="font-weight: bold;">bold face</span>.<br> +</p> +<p>The Tungsten Graphics, Inc. OpenGL subset library is hereafter +refered to as <span style="font-style: italic;">the subset.</span><br> +<br> +</p> +<h1>2. Primitive Specification</h1> +<h2>2.1 glBegin, glEnd and glVertex Commands</h2> +The basic rendering primitives are points, lines and triangles. + Quadrilaterals and polygons are composed of triangles. + Primitives are drawn with the <span style="font-weight: bold;">glBegin</span> +and <span style="font-weight: bold;">glEnd</span> commands and a subset +of the <span style="font-weight: bold;">glVertex</span> commands:<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glBegin</span>(GLenum<span + style="font-style: italic;">mode</span>)<br> +void <span style="font-weight: bold;">glEnd</span>(void)<br> +<br> +void <span style="font-weight: bold;">glVertex2f</span>(GLfloat <span + style="font-style: italic;">x</span>, GLfloat <span + style="font-style: italic;">y</span>)<br> +void <span style="font-weight: bold;">glVertex2fv</span>(const GLfloat +*<span style="font-style: italic;">v</span>)<br> +void <span style="font-weight: bold;">glVertex3f</span>(GLfloat <span + style="font-style: italic;">x</span>, GLfloat <span + style="font-style: italic;">y</span>, GLfloat <span + style="font-style: italic;">z</span>)<br> +void <span style="font-weight: bold;">glVertex3fv</span>(const GLfloat +*<span style="font-style: italic;">v</span>)<br> +</div> +<br> +The <span style="font-style: italic;">mode</span> parameter to <span + style="font-weight: bold;">glBegin</span> may be one of the following<br> +<br> +<div style="margin-left: 40px;">GL_POINTS - a series of individual +points<br> +GL_LINES - a series of disjoint line segments<br> +GL_LINE_STRIP - series of connected line segments<br> +GL_LINE_LOOP - a closed loop of line segments<br> +GL_TRIANGLES - a series of individual triangles<br> +GL_TRIANGLE_STRIP - a connected strip of triangles<br> +GL_TRIANGLE_FAN - a sequence of triangles all sharing a common vertex<br> +GL_QUADS - a sequence of individual quadrilaterals<br> +GL_QUAD_STRIP - a connected strip of quadrilaterals<br> +GL_POLYGON - a closed, convex polygon<br> +<br> +</div> +<br> +The <span style="font-weight: bold;">glVertex</span> commands take two +or three floating point coordinates, or a pointer to an array of two or +three floating point coordinates. OpenGL vertices are actually +4-element homogeneous coordinates. The fourth component, +unspecified by the <span style="font-weight: bold;">glVertex</span> +commands, is one.<br> +<br> +<span style="font-weight: bold;">glVertex</span> commands defined by +OpenGL but not listed above, are omitted from the subset.<br> +<br> +<h2>2.2 Other Per-vertex Commands<br> +</h2> +The <span style="font-weight: bold;">glColor</span> and <span + style="font-weight: bold;">glTexCoord</span> commands may be used to +specify colors and texture coordinates for each vertex:<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glColor3f</span>(GLfloat<span + style="font-style: italic;">red</span>, GLfloat <span + style="font-style: italic;">green</span>, GLfloat <span + style="font-style: italic;">blue</span>)<br> +void <span style="font-weight: bold;">glColor3fv</span>(const GLfloat *<span + style="font-style: italic;">rgb</span>)<br> +void <span style="font-weight: bold;">glColor4f</span>(GLfloat <span + style="font-style: italic;">red,</span> GLfloat <span + style="font-style: italic;">green,</span> GLfloat <span + style="font-style: italic;">blue,</span> GLfloat <span + style="font-style: italic;">alpha</span>)<br> +void <span style="font-weight: bold;">glColor4fv</span>(const GLfloat *<span + style="font-style: italic;">rgba</span>)<br> +void <span style="font-weight: bold;">glTexCoord2f</span>(GLfloat <span + style="font-style: italic;">s</span>, GLfloat<span + style="font-style: italic;"> t</span>)<br> +void <span style="font-weight: bold;">glTexCoord2fv</span>(const +GLfloat *<span style="font-style: italic;">c</span>)<br> +<br> +</div> +The <span style="font-weight: bold;">glColor</span> commands specify +the color and optionally, the alpha value, for subsequent vertices. + For the <span style="font-weight: bold;">glColor3</span> commands, +alpha is set to one.<br> +<br> +The <span style="font-weight: bold;">glTexCoord2</span> commands +specify the texture coordinate for subsequent vertices. Texture +coordinates are actually four-component coordinates: (s, t, r, q). + The <span style="font-weight: bold;">glTexCoord2</span> commands +set s and t explicitly. The r and q components are zero and one, +respectively.<br> +<br> +<span style="font-weight: bold;">glColor</span> and <span + style="font-weight: bold;">glTexCoord</span> commands defined by OpenGL +but not listed above, are omitted from the subset. Furthermore, +the <span style="font-weight: bold;">glEdgeFlag, glColorIndex</span> and <span + style="font-weight: bold;">glNormal</span> commands are also omitted +from the subset.<br> +<br> +Only <span style="font-weight: bold;">glVertex, glColor</span> and <span + style="font-weight: bold;">glTexCoord</span> commands are allowed +between <span style="font-weight: bold;">glBegin</span> and <span + style="font-weight: bold;">glEnd.</span> Calling any other +command between <span style="font-weight: bold;">glBegin</span> and <span + style="font-weight: bold;">glEnd</span> will result in the error +GL_INVALID_OPERATION.<br> +<br> +<h2>2.3 Unsupported Commands</h2> +None of the following OpenGL commands related to primitive +specification are supported by the subset:<br> +<br> +<div style="margin-left: 40px;">Vertex array commands:<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glVertexPointer, +glColorPointer, glIndexPointer, glTexCoordPointer, glEdgeFlagPointer, +glNormalPointer, glInterleavedArrays, glArrayElement, glDrawArrays, +glDrawElements, glDrawRangeElements, glEnableClientState, +glDisableClientState</span><br> +</div> +</div> +<div style="margin-left: 40px;"><br> +Rectangle commands:<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glRects, +glRecti, glRectf, glRectd, glRectsv, glRectiv, glRectfv, glRectdv,<br> +<br> +</span></div> +</div> +<div style="margin-left: 40px;">Lighting commands:<br> +</div> +<div style="margin-left: 80px;"><span style="font-weight: bold;">glMaterial<br> +</span><br> +</div> +<div style="margin-left: 40px;"> Evaluator commands:<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glEvalCoord, +glEvalPoint</span><br> +<br> +</div> +</div> +<h1>3. Coordinate Transformation</h1> +<h2>3.1 Vertex Transformation</h2> +Vertex coordinates are transformed by the current modelview and +projection matrices then mapped to window coordinates as specified by +the viewport. The following coordinate transformation commands are +supported by the subset<br> +<br> +<div style="margin-left: 40px; font-weight: bold;">glMatrixMode<span + style="font-weight: normal;">(GLenum <span style="font-style: italic;">mode</span>)</span><br> +glLoadIdentity<span style="font-weight: normal;">(void)</span><br> +glPushMatrix<span style="font-weight: normal;">(void)</span><br> +glPopMatrix<span style="font-weight: normal;">(void)</span><br> +glLoadMatrixf<span style="font-weight: normal;">(const GLfloat *<span + style="font-style: italic;">m</span>)</span><br> +glMultMatrixf<span style="font-weight: normal;">(const GLfloat *<span + style="font-style: italic;">m</span>)</span><br> +glRotatef<span style="font-weight: normal;">(GLfloat <span + style="font-style: italic;">angle</span>, GLfloat <span + style="font-style: italic;">x</span>, GLfloat <span + style="font-style: italic;">y</span>, GLfloat <span + style="font-style: italic;">z</span>)</span><br> +glTranslatef<span style="font-weight: normal;">(GLfloat <span + style="font-style: italic;">x</span>, GLfloat <span + style="font-style: italic;">y</span>, GLfloat <span + style="font-style: italic;">z</span>)</span><br> +glScalef<span style="font-weight: normal;">(GLfloat <span + style="font-style: italic;">x</span>, GLfloat <span + style="font-style: italic;">y</span>, GLfloat <span + style="font-style: italic;">z</span>)<br> +<span style="font-weight: bold;">glFrustum(</span>GLfloat <span + style="font-style: italic;">left,</span> GLfloat <span + style="font-style: italic;">right,</span> GLfloat <span + style="font-style: italic;">bottom,</span> GLfloat <span + style="font-style: italic;">top,</span> GLfloat <span + style="font-style: italic;">near,</span> GLfloat <span + style="font-style: italic;">far</span>)</span><br> +<span style="font-weight: normal;"><span style="font-weight: bold;">glOrtho(</span>GLfloat<span + style="font-style: italic;">left,</span> GLfloat <span + style="font-style: italic;">right,</span> GLfloat <span + style="font-style: italic;">bottom,</span> GLfloat <span + style="font-style: italic;">top,</span> GLfloat <span + style="font-style: italic;">near,</span> GLfloat <span + style="font-style: italic;">far</span>)</span><br> +glViewport<span style="font-weight: normal;">(GLint <span + style="font-style: italic;">x</span>, GLint <span + style="font-style: italic;">y</span>, GLsize <span + style="font-style: italic;">width,</span> GLsizei <span + style="font-style: italic;">height</span>)</span><br> +</div> +<br> +The <span style="font-weight: bold;">glMatrixMode</span> command +specifies the <span style="font-style: italic;">current matrix.</span> + The mode parameter may be GL_MODELVIEW or GL_PROJECTION to specify +the modelview matrix or projection matrix. Subsequent matrix +commands will effect the current matrix. Also associated with the +modelview and projection matrices are a modelview matrix stack and +projection matrix stack.<br> +<br> +The <span style="font-weight: bold;">glLoadIdentity</span> command +replaces the current matrix with the identity matrix.<br> +<br> +The <span style="font-weight: bold;">glPushMatrix</span> command pushes +a copy of the current matrix onto either the modelview matrix stack or +the projection matrix stack. The <span style="font-weight: bold;">glPopMatrix</span> +command replaces the current matrix with a copy of the top matrix off +the modelview matrix stack or projection matrix stack, the pops the +stack. Matrix stacks are useful for traversing and rendering +heirarchal models.<br> +<br> +The <span style="font-weight: bold;">glMultMatrixf</span> command +post-multiplies the current matrix by the specified matrix.<br> +<br> +The <span style="font-weight: bold;">glRotatef</span> command +post-multiplies the current matrix by a rotation matrix defined by the +angle and rotation axis defined by x, y and z.<br> +<br> +The <span style="font-weight: bold;">glTranslatef</span> command +post-multiplies the current matrix by a translation matrix defined by +the x, y and z translation parameters.<br> +<span style="font-weight: bold;"></span><br> +The <span style="font-weight: bold;">glScalef</span> command +post-multiplies the current matrix by a scaling matrix defined by the x, +y and z scale factors.<br> +<span style="font-weight: bold;"></span><br> +The <span style="font-weight: bold;">glFrustum</span> command +post-multiplies the current matrix by a persperctive projection matrix. + The <span style="font-style: italic;">near</span> and <span + style="font-style: italic;">far</span> values specify the position of +the hither and yon Z-axis clipping planes. The <span + style="font-style: italic;">left, right, bottom</span> and <span + style="font-style: italic;">top</span> parameters are the X and Y +extents at the near clipping plane. <span + style="font-weight: bold;">glFrustum</span> is normally used to modify +the projection matrix.<br> +<br> +The <span style="font-weight: bold;">glOrtho</span> command +post-multiplies the current matrix by an orthographic projection matrix. + The <span style="font-style: italic;">near</span> and <span + style="font-style: italic;">far</span> values specify the position of +the hither and yon Z-axis clipping planes. The <span + style="font-style: italic;">left, right, bottom</span> and <span + style="font-style: italic;">top</span> parameters specify the X and +Y-axis clipping planes. <span style="font-weight: bold;">glOrtho</span> +is normally used to modify the projection matrix.<br> +<br> +The <span style="font-weight: bold;">glViewport</span> command +specifies the mapping of coordiantes from normalized device coordinates +to window coordinates. The <span style="font-style: italic;">x</span> +and <span style="font-style: italic;">y</span> parameters specify the +viewport's lower-left corner in the window and the <span + style="font-style: italic;">width</span> and <span + style="font-style: italic;">height</span> parameters specify the size +of the viewport. <span style="font-weight: bold;">glViewport</span> +does not effect the current matrix.<br> +<br> +A coordinate transformed to window coordinates is hereafter known as (x<sub>w</sub>, +y<sub>w</sub>, z<sub>w</sub>).<br> +<br> +The following double-precision coordinate transformation commands are +omitted from the subset:<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;"><br> +glLoadMatrixd, glMultMatrixd, glRotated, glTranslated, glScaled</span><br + style="font-weight: bold;"> +</div> +<br> +Furthermore, the <span style="font-weight: bold;">glDepthRange</span> +command, which maps normalized device coordinates to Z buffer values +(the Z-axis companion the the X/Y-axis <span style="font-weight: bold;">glViewport</span> +command) is omitted from the subset. The near and far depth range +values are always zero and one, respectively.<br> +<br> +<h2>3.2 Clipping</h2> +View-volume clipping automatically discards or trims primitives which +lie completely or partially outside of the view volume specified by <span + style="font-weight: bold;">glFrustum</span> and <span + style="font-weight: bold;">glOrtho</span>. Note that the <span + style="font-weight: bold;">glViewport</span> command does not define a +clipping region.<br> +<br> +Clipping occurs in <span style="font-style: italic;">clip coordinate +space - </span>the coordinates produced after applying the projection +matrix.<br> +<br> +<h2>3.3 Current Raster Position</h2> +The current raster position specifies the location for drawing images +with <span style="font-weight: bold;">glBitmap.</span> The current +raster position is set with the commands:<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glRasterPos2f</span>(GLfloat<span + style="font-style: italic;">x</span>, GLfloat <span + style="font-style: italic;">y</span>)<br> +void <span style="font-weight: bold;">glRasterPos2fv</span>(const +GLfloat *<span style="font-style: italic;">v</span>)<br> +void <span style="font-weight: bold;">glRasterPos2i</span>(GLint <span + style="font-style: italic;">x</span>, GLint <span + style="font-style: italic;">y</span>)<br> +void <span style="font-weight: bold;">glRasterPos2iv</span>(const +GLint *<span style="font-style: italic;">v</span>)<br> +</div> +<br> +<span style="font-weight: bold;">glRasterPos</span> specifies a +4-component coordinate (x, y, 0, 1). The coordinate is processed +like a vertex; it is transformed by the modelview matrix, the projection +matrix and mapped to the viewport. The resulting window coordinate +is stored as the current raster position. The coordinate is +clipped-tested against the frustum like a vertex. If the +coordinate is clipped, then the current raster position becomes invalid +and subsequent <span style="font-weight: bold;">glBitmap</span> commands +have no effect.<br> +<br> +<span style="font-weight: bold;">glRasterPos</span> also updates the +current raster color and texture coordinates. The current raster +color is updated (copied) from the current color (as specified by <span + style="font-weight: bold;">glColor</span>). The current raster +texture coordinate is updated (copied) from the current texture +coordinate (as specified by <span style="font-weight: bold;">glTexCoord</span>).<br> +<br> +<h2>3.4 Unsupported Commands</h2> +OpenGL lighting, automatic texture coordinate generation and +user-defined clipping planes are not supported by the subset and the +following commands are omitted.<br> +<br> +<div style="margin-left: 40px;">User-defined clip plane commands:<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glClipPlane</span><br> +</div> +<span style="font-weight: bold;"></span></div> +<br> +<div style="margin-left: 40px;">Lighting commands:</div> +<div style="margin-left: 80px;"><span style="font-weight: bold;">glLightModel, +glLight, glColorMaterial</span><br> +</div> +<br> +<div style="margin-left: 40px;">Automatic texture coordinate generation +commands:<br> +</div> +<div style="margin-left: 40px;"> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glTexGen</span><br + style="font-weight: bold;"> +</div> +<br> +</div> +<h1>4. Rasterization</h1> +This section describes the commands and options for drawing points, +lines, triangles and bitmaps. <span style="font-style: italic;">Rasterization</span> +is the term for the process which produces fragments from the geometric +description of a primitive (a point, line, polygon or bitmap). For +example, given the two coordinates for the end-points of a line segment, +rasterization determines which pixels in the frame buffer to modify to <span + style="font-style: italic;">draw</span> the line. A fragment is a +tuple which consists of a window coordinate, colors and texture +coordinates. The fragments produced by rasterization are +subsequently processed by the per-fragment operations described later.<br> +<br> +<h2>4.1 Point Rasterization</h2> +Points are rendered with the command sequence <span + style="font-weight: bold;">glBegin</span>(GL_POINTS), <span + style="font-weight: bold;">glVertex</span>, ... <span + style="font-weight: bold;">glEnd</span>. The window coordinate (x<sub>w</sub>, +y<sub>w</sub>, z<sub>w</sub>) is truncated to rasterize the point. + The truncated coordinate with its associated color and texture +coordinate is sent as a single fragment to the per-fragment processing +stages.<br> +<br> +The <span style="font-weight: bold;">glPointSize</span> command is not +supported; only 1-pixel points are supported.<br> +<br> +Point smoothing (antialiasing) is also not supported.<br> +<br> +<h2>4.2 Line Rasterization</h2> +Lines are rendered with the command sequence <span + style="font-weight: bold;">glBegin</span>(<span + style="font-style: italic;">mode</span>), <span + style="font-weight: bold;">glVertex</span>, <span + style="font-weight: bold;">glVertex</span>, ... <span + style="font-weight: bold;">glEnd</span> where <span + style="font-style: italic;">mode</span> is one of GL_LINES, +GL_LINE_STRIP or GL_LINE_LOOP. Lines are rasterizerized as +described in the OpenGL specification. Note that OpenGL uses the <span + style="font-style: italic;">half-open</span> convention for drawing +lines: the last fragment in a line segment is omitted so that endpoint +pixels shared by two line segments will only be drawn once instead of +twice.<br> +<br> +<h3>4.2.1 Line Width</h3> +The width of lines can be controlled by<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glLineWidth</span>(GLfloat<span + style="font-style: italic;">width</span>)<br> +</div> +<br> +where <span style="font-style: italic;">width</span> is the line width +in pixels. The width defaults to 1.0. Attempting to set the +width to a value less than or equal to zero will raise the error +GL_INVALID_VALUE.<br> +<br> +<h3>4.2.2 Line Stipple<br> +</h3> +Lines may be stippled (i.e dashed) with the command<br> +<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glLineStipple</span>(GLint<span + style="font-style: italic;">factor</span>, GLushort <span + style="font-style: italic;">pattern</span>)<br> +</div> +<br> +As described in the OpenGL specification, <span + style="font-style: italic;">pattern</span> describes an on/off pattern +for the fragments produced by rasterization and <span + style="font-style: italic;">factor</span> specifies how many subsequent +fragments are kept or culled for each pattern bit. Line stippling +can be enabled or disabled by the commands <span + style="font-weight: bold;">glEnable</span>(GL_LINE_STIPPLE) and <span + style="font-weight: bold;">glDisable</span>(GL_LINE_STIPPLE).<br> +<br> +<h3>4.2.3 Line Antialiasing</h3> +Lines may be antialiased. For antialiased lines, each fragment +produced by rasterization is assigned a <span + style="font-style: italic;">coverage value</span> which describes how +much of the fragment's area is considered to be <span + style="font-style: italic;">inside</span> the line. Later, the +alpha value of each fragment is multiplied by the coverage value. + By blending the fragments into the frame buffer, the edges of +lines appear smoothed.<br> +<br> +Line antialiasing can be enabled or disabled with the commands <span + style="font-weight: bold;">glEnable</span>(GL_LINE_SMOOTH) and <span + style="font-weight: bold;">glDisable</span>(GL_LINE_SMOOTH).<br> +<br> +<h2>4.3 Polygon Rasterization</h2> +Polygons, quadrilaterals and triangles share the same polygon +rasterization options. <br> +<br> +Triangles are rendererd by the command sequence <span + style="font-weight: bold;">glBegin</span><span + style="font-style: italic;"><span style="font-style: italic;">(mode</span></span>),<span + style="font-weight: bold;">glVertex</span>, <span + style="font-weight: bold;">glVertex</span>, ... <span + style="font-weight: bold;">glEnd</span> where <span + style="font-style: italic;">mode</span> may be one of GL_TRIANGLES, +GL_TRIANGLE_STRIP or GL_TRIANGLE_FAN.<span style="font-weight: bold;"></span> + For GL_TRIANGLES mode, the number of vertices should be a multiple +of three - extra vertices will be ignored. For GL_TRIANGLE_STRIP +and GL_TRIANGLE_FAN, at least three vertices should be specified. + If less than three are specified, nothing is drawn. <br> +<br> +Quadrilaterals are <span style="font-weight: bold;"></span>rendererd +by the command sequence <span style="font-weight: bold;">glBegin</span>(<span + style="font-style: italic;"><span style="font-style: italic;">mode</span></span>),<span + style="font-weight: bold;">glVertex</span>, <span + style="font-weight: bold;">glVertex</span>, ... <span + style="font-weight: bold;">glEnd</span> where <span + style="font-style: italic;">mode</span> may be one of GL_QUADS or +GL_QUAD_STRIP.<span style="font-weight: bold;"></span> For +GL_QUADS, the number of vertices should be a multiple of four - extra +vertices will be ignored. For GL_QUAD_STRIP, the number of +vertices should be even and at least four. Extra vertices (one) +will be ignored.<br> +<br> +Convex polygons are <span style="font-weight: bold;"></span>rendererd +by the command sequence <span style="font-weight: bold;">glBegin</span><span + style="font-style: italic;"><span style="font-style: italic;"></span></span>(GL_POLYGON),<span + style="font-weight: bold;">glVertex</span>, <span + style="font-weight: bold;">glVertex</span>, ... <span + style="font-weight: bold;">glEnd</span>.<span + style="font-style: italic;"></span><span style="font-weight: bold;"></span> + If less than three vertices are specified, nothing is drawn.<br> +<br> +<h3>4.3.1 Polygon Orientation</h3> +The <span style="font-style: italic;">winding order</span> of vertices +(clockwise or counter-clockwise) is significant. It is used to +determine the <span style="font-style: italic;">front-facing</span> or <span + style="font-style: italic;">back-facing</span> orientation of polygons. + By default, a front-facing polygon's vertices are in +counter-clockwise order (in window coordinates). Figures 2.4 and +2.5 of the OpenGL 1.2.1 specification illustrate the winding order for +front-facing triangles and quadrilaterals, respectively.<br> +<br> +The command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glFrontFace</span>(GLenum<span + style="font-style: italic;">mode</span>)<br> +</div> +<br> +specifies whether clockwise or counter-clockwise winding indicates a +front-facing polygon. If <span style="font-style: italic;">mode</span> +is GL_CW then polygons with clockwise winding are front-facing. If <span + style="font-style: italic;">mode</span> is GL_CCW then polygons with +counter-clockwise winding are front-facing. The default value is +GL_CCW. If <span style="font-style: italic;">mode</span> is not +GL_CCW or GL_CW then the error GL_INVALID_ENUM will be raised.<span + style="font-style: italic;"></span><span style="font-style: italic;"></span><br> +<br> +<h3>4.3.2 Polygon Culling</h3> +Polygons may be culled (discarded) depending on whether they are +front-facing or back-facing. The command<br> +<br> +<div style="margin-left: 40px;">void<span style="font-weight: bold;"> +glCullFace</span>(GLenum <span style="font-style: italic;">mode</span>)<br> +</div> +<br> +specifies whether front-facing, back-facing or all polygons should be +culled. If <span style="font-style: italic;">mode</span> is +GL_FRONT then front-facing polygons will be culled. If <span + style="font-style: italic;">mode</span> is GL_BACK then back-facing +polygons will be culled. Otherwise, if <span style="font-style: italic;">mode</span> +is GL_FRONT_AND_BACK then all polygons will be culled. Any other +value for <span style="font-style: italic;">mode</span> will raise the +error GL_INVALID_ENUM.<br> +<br> +Polygon culling is enabled and disabled with the commands <span + style="font-weight: bold;">glEnable</span>(GL_CULL_FACE) and <span + style="font-weight: bold;">glDisable</span>(GL_CULL_FACE), +respectively.<br> +<br> +<h3>4.3.3 Polygon Fill Mode</h3> +The command<br> +<br> +<div style="margin-left: 40px;">void<span style="font-weight: bold;"><span + style="font-weight: bold;"> </span><span style="font-weight: bold;"></span>glPolygonMode</span>(GLenum<span + style="font-style: italic;">face</span>, GLenum <span + style="font-style: italic;">mode</span>)<br> +</div> +<br> +controls whether polyons are filled, outlined or drawn with a point at +each vertex. The <span style="font-style: italic;">face</span> +parameter must be GL_FRONT_AND_BACK. The values GL_FRONT and +GL_BACK are not permitted by the subset. If <span + style="font-style: italic;">mode</span> is GL_FILL then the polygon +will be filled (the default). If <span style="font-style: italic;">mode</span> +is GL_LINE then the polygon will be rendered as if it were specified by <span + style="font-weight: bold;">glBegin</span>(GL_LINE_LOOP). If <span + style="font-style: italic;">mode</span> is GL_POINT then the polygon +will be rendered as if it were specified with <span + style="font-weight: bold;">glBegin</span>(GL_POINTS). Any other +values for <span style="font-style: italic;">face</span> or <span + style="font-style: italic;">mode</span> will ra<span + style="font-style: italic;"></span>ise the error GL_INVALID_ENUM.<br> +<br> +<h3>4.3.4 Polygon Antialiasing</h3> +Polygons may be antialiased in order to smooth their edges. + Polygon antialiasing is enabled and disabled with the commands <span + style="font-weight: bold;">glEnable</span>(GL_POLYGON_SMOOTH) and <span + style="font-weight: bold;">glDisable</span>(GL_POLYGON_SMOOTH).<br> +<br> +When polygon antialasing is enabled each fragment produced by polygon, +triangle and quadrilateral rasterization will be given a <span + style="font-style: italic;">coverage</span> value which indicates how +much of the fragment is covered by the polygon. Fragments +completely inside the polygon have coverage 1.0. Fragments +completely outside the polygon have zero coverage (in theory). + Fragments which intersect the polygon's edge have a coverage value +in the range (0, 1).<br> +<br> +The fragment's alpha value is multiplied by the coverage value. + By enabling the appropriate blending mode, polygon edges will +appear smoothed.<br> +<br> +<h3> 4.3.5 Other Polygon Features</h3> +Polygon stippling and the <span style="font-weight: bold;">glPolygonStipple</span> +command are not supported by the subset.<br> +<br> +Polygon depth offset and the <span style="font-weight: bold;">glPolygonOffset</span> +command are not supported by the subset.<br> +<br> +<h2>4.4 Shading</h2> +The command<br> +<br> +<div style="margin-left: 40px;"> void <span style="font-weight: bold;">glShadeModel</span>(GLenum<span + style="font-style: italic;">mode</span>)<br> +</div> +<br> +determines whether colors are interpolated between vertices during +rasterization. If <span style="font-style: italic;">mode</span> is +GL_FLAT then vertex colors are not interpolated. The color used +for drawing lines, triangles and quadrilaterals is that of the last +vertex used to specify each primitive. For polygons, the color of +the first vertex specifies the color for the entire polygon. If <span + style="font-style: italic;">mode</span> is GL_SMOOTH then vertex colors +are linearly interpolated to produce the fragment colors.<br> +<br> +<h2>4.5 Bitmap Rasterization</h2> +In OpenGL, a bitmap is a monochromatic, binary image in which each +image element (or pixel) is represented by one bit. Fragments are +only generated for the bits (pixels) which are set. Bitmaps are +commonly used to draw text (glyphs) and markers.<br> +<br> +A bitmap is drawn with the command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glBitmap</span>(GLsizei<span + style="font-style: italic;">width</span>, GLsizei <span + style="font-style: italic;">height</span>, GLfloat <span + style="font-style: italic;">xOrig</span>, GLfloat <span + style="font-style: italic;">yOrig</span>, GLfloat <span + style="font-style: italic;">xMove</span>, GLfloat <span + style="font-style: italic;">yMove</span>, const GLubyte *<span + style="font-style: italic;">image</span>)<br> +</div> +<br> +<span style="font-style: italic;">width </span>and <span + style="font-style: italic;">height</span> specify the image size in +pixels. <span style="font-style: italic;">xOrig</span> and <span + style="font-style: italic;">yOrig</span> specify the bitmap origin. + <span style="font-style: italic;">xMove</span> and <span + style="font-style: italic;">yMove</span> are added to the current +raster position after the bitmap is rasterized. <span + style="font-style: italic;">image</span> is a pointer to the bitmap +data.<br> +<br> +If the current raster position is not valid, <span + style="font-weight: bold;">glBitmap</span> has no effect.<br> +<br> +<h3>4.5.1 Unpacking</h3> +The first step in bitmap rendering is <span style="font-style: italic;">unpacking. + </span>Unpacking is the process of extracting image data from +client memory subject to byte swapping, non-default row strides, etc. + The unpacking parameters are specified with the command<br> +<br> +<div style="margin-left: 40px;">void<span style="font-weight: bold;"> +glPixelStorei</span>(GLenum pname, GLint value)<br> +</div> +<span style="font-style: italic;"></span><br> +The following unpacking parameters may be set:<br> +<br> +<table cellpadding="2" cellspacing="2" border="1" + style="text-align: left; width: 90%; margin-left: auto; margin-right: auto;"> + <tbody> + <tr> + <td style="vertical-align: top;">Parameter (<span + style="font-style: italic;">pname</span>)<br> + </td> + <td style="vertical-align: top;">Value (<span + style="font-style: italic;">value</span>)<br> + </td> + <td style="vertical-align: top;">Default<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_UNPACK_ROW_LENGTH<br> + </td> + <td style="vertical-align: top;">Width of the image in memory, in +pixels.<br> + </td> + <td style="vertical-align: top;">0<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_UNPACK_SKIP_PIXELS<br> + </td> + <td style="vertical-align: top;">Number of pixels to skip +horizontally in each image row in memory.<br> + </td> + <td style="vertical-align: top;">0<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_UNPACK_SKIP_ROWS<br> + </td> + <td style="vertical-align: top;">Number of pixels to skip +vertically in the image in memory before unpacking.<br> + </td> + <td style="vertical-align: top;">0<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_UNPACK_LSB_FIRST<br> + </td> + <td style="vertical-align: top;">GL_FALSE indicates that the most +significant bit is unpacked first from each byte. GL_TRUE +indicates that the least significant bit is unpacked first from each +byte. <br> + </td> + <td style="vertical-align: top;">GL_FALSE<br> + </td> + </tr> + </tbody> +</table> +<br> +<br> +The GL_UNPACK_ROW_LENGTH, GL_UNPACK_SKIP_PIXELS and GL_UNPACK_SKIP_ROWS +parameters allow a sub-region of a bitmap image in memory to be drawn, +rather than the whole image. GL_UNPACK_ROW_LENGTH specifies the +width of the image in memory. If it's zero, the <span + style="font-style: italic;">width</span> parameter to <span + style="font-weight: bold;">glBitmap</span> specifies the width of the +image in memory. GL_UNPACK_SKIP_PIXELS and GL_UNPACK_SKIP_ROWS +specify the (x, y) offset of the image to render within the image in +memory.<br> +<br> +GL_UNPACK_LSB_FIRST determines whether the least significant or most +significant bit in each byte is unpacked first. Unpacking occurs +in left to right order (in image space).<br> +<br> +The value of bit (i, j) of the image (where i is the image row and j is +the image column) is found as follows:<br> +<br> +<div style="margin-left: 40px;">rowLength = (GL_UNPACK_ROW_LENGTH != 0) +? GL_UNPACK_ROW_LENGTH : <span style="font-style: italic;">width</span>;<br> +<br> +byte = <span style="font-style: italic;">image</span>[((rowLength + 7) +/ 8) * (i + GL_SKIP_ROWS) + (j + GL_SKIP_PIXELS) / 8];<br> +<br> +if (GL_UNPACK_LSB_FIRST != 0)<br> + bitMask = 1 << ((j + GL_SKIP_PIXELS) % 8);<br> +else<br> + bitMask = 128 >> ((j + GL_SKIP_PIXELS) % 8);<br> +<br> +if (byte & bitMask)<br> + bit = 1;<br> +else<br> + bit = 0;<br> +<br> +</div> +<span style="font-style: italic;"><span style="font-style: italic;"></span></span> +<h3>4.4.2 Rasterization</h3> +If the current raster position is (x<sub>rp</sub>, y<sub>rp</sub>, z<sub>rp</sub>, +w<sub>rp</sub>), then the bitmap is rasterized according to the +following algorithm:<br> +<br> +for (j = 0; j < <span style="font-style: italic;">height</span>; +j++) {<br> + for (i = 0; i < <span style="font-style: italic;">width</span>; +i++) {<br> + if (bit(i,j)) {<br> + fragment.x = +floor(x<sub>rp</sub> - <span style="font-style: italic;">xOrig</span>) ++ i;<br> + fragment.y = +floor(y<sub>rp</sub> - <span style="font-style: italic;">yOrig</span>) ++ j;<br> + fragment.color += GL_CURRENT_RASTER_COLOR;<br> + +fragment.texture = GL_CURRENT_RASTER_TEXTURE_COORDS;<br> + +ProcessFragment(fragment)<br> + }<br> + }<br> +}<br> +<br> +After the bitmap has been rendered the current raster position is +updated as follows:<br> +<br> +<div style="margin-left: 40px;">x<sub>rp</sub> = x<sub>rp</sub> + <span + style="font-style: italic;">xMove</span><br> +y<sub>rp</sub> = y<sub>rp</sub> + <span style="font-style: italic;">yMove</span><br> +</div> +<br> +<h3>4.4.3 Per-fragment Operations</h3> +XXX supported? See issue in appendix A.<br> +<br> +<br> +<h1>5. Texture Mapping<br> +</h1> +There are four elements to texture mapping: texture coordinate +specification, texture image specification, texture sampling and texture +application.<br> +<br> +<h2>5.1 Texture Image Specification</h2> +A texture image is specified with the command:<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glTexImage2D</span>(GLenum<span + style="font-style: italic;"> target</span>, GLint <span + style="font-style: italic;">level</span>, GLint <span + style="font-style: italic;">internalFormat,</span> GLsizei <span + style="font-style: italic;">width,</span> GLsizei <span + style="font-style: italic;">height,</span> GLint <span + style="font-style: italic;">border,</span> GLenum <span + style="font-style: italic;">format,</span> GLenum <span + style="font-style: italic;">type,</span> const GLvoid *<span + style="font-style: italic;">pixels</span> )<br> +</div> +<br> +<span style="font-style: italic;">target</span> must be GL_TEXTURE_2D. + <span style="font-style: italic;">level </span>indicates the +mipmap level for mipmap textures. <span style="font-style: italic;">internalFormat</span> +is a hint to indicate the prefered internal storage format for the +texture. <span style="font-style: italic;">width</span> and <span + style="font-style: italic;">height </span>indicate the image size in +pixels (or texels). <span style="font-style: italic;">border </span>must +be zero. <span style="font-style: italic;">format</span> and <span + style="font-style: italic;">type</span> describe the pixel format and +data type for the incoming image. <span style="font-style: italic;">pixels</span> +points to the incoming texture image. These parameters are +described in more detail below.<br> +<br> +<h3>5.1.1 Texture Image Size and Mipmaps</h3> +<h3><span style="font-style: italic;"></span></h3> +Texture images must have dimensions (width and height) that are powers +of two. For example: 256 x 256, 32 x 1024, 1 x 8, etc. That is, it +must be the case that <span style="font-style: italic;">width </span>= +2<sup>n</sup> and <span style="font-style: italic;">height</span> = 2<sup>m</sup> +for some positive integers n and m.<br> +<br> +Mipmapping is a method of antialiasing or filtering textures to improve +their appearance. A mipmap is a set of images consisting of a base +image and a set of filtered, reduced-resolution images. If the +base image (<span style="font-style: italic;">level</span>=0) is of +width 2<sup>n</sup> and height 2<sup>m</sup> then the level 1 image must +be of width 2<sup>n-1</sup> and height 2<sup>m-1</sup>. Each mipmap +level is half the width and height of the previous level, or at least +one. The last mipmap level has a width and height of one.<br> +<br> +The following is an example of a mipmap's image levels:<br> +<br> +<table cellpadding="2" cellspacing="2" border="1" + style="text-align: left; width: 50%; margin-left: auto; margin-right: auto;"> + <tbody> + <tr> + <td style="vertical-align: top;">mipmap level<br> + </td> + <td style="vertical-align: top;">width<br> + </td> + <td style="vertical-align: top;">height<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">0<br> + </td> + <td style="vertical-align: top;">256<br> + </td> + <td style="vertical-align: top;">64<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">128<br> + </td> + <td style="vertical-align: top;">32<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">2<br> + </td> + <td style="vertical-align: top;">64<br> + </td> + <td style="vertical-align: top;">16<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">3<br> + </td> + <td style="vertical-align: top;">32<br> + </td> + <td style="vertical-align: top;">8<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">4<br> + </td> + <td style="vertical-align: top;">16<br> + </td> + <td style="vertical-align: top;">4<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">5<br> + </td> + <td style="vertical-align: top;">8<br> + </td> + <td style="vertical-align: top;">2<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">6<br> + </td> + <td style="vertical-align: top;">4<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">7<br> + </td> + <td style="vertical-align: top;">2<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">8<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + </tr> + </tbody> +</table> +<br> +If the <span style="font-style: italic;">width</span> or <span + style="font-style: italic;">height</span> parameters are not powers of +two, the error GL_INVALID_VALUE is raised. If the image levels in +a mipmap do not satisfy the restrictions listed above the texture is +considered to be <span style="font-style: italic;">inconsistant</span> +and the system will behave as if the texturing is disabled.<br> +<br> +<h3>5.1.2 Texture Image Formats and Unpacking</h3> +The <span style="font-weight: bold;">glTexImage2D</span> command's <span + style="font-style: italic;"><span style="font-weight: bold;"></span></span><span + style="font-style: italic;">format</span> parameter indicates the +number and type of color channels per pixel in the incoming image. +Accepted values are GL_ALPHA, GL_RGB and GL_RGBA. The <span + style="font-style: italic;">type</span> parameter indicates the +datatype for each component of a pixel and must be either +GL_UNSIGNED_BYTE.<br> +<br> +The <span style="font-style: italic;">internalFormat</span> parameter +indicates the desired internal format for the texture and may be either +GL_INTENSITY8, GL_RGB5 or GL_RGBA8.<br> +<br> +<h2>5.2 Texture Coordinates</h2> +Texture coordinates control the mapping from local polygon space to +texture image space. Texture coordinates are set for each vertex +with the <span style="font-weight: bold;">glTexCoord</span> commands. + During line and polygon rasterization the vertex texture +coordinates are interpolated across the primitive to produce a texture +coordinate for each fragment. The fragment texture coordinates are +used to sample the current texture image.<br> +<br> +<h2>5.3 Texture Sampling</h2> +<h3>5.3.1 Texture Coordinate Wrapping</h3> +Texture coordinates are normally in the interval [0, 1]. Values +outside that range are processed according to the <span + style="font-style: italic;">texture wrap mode</span>. The +texture wrap mode, and other parameters, are set with the commands<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glTexParameteri</span>(GLenum<span + style="font-style: italic;"> target</span>, GLenum <span + style="font-style: italic;">pname</span>, GLint <span + style="font-style: italic;">value</span>)<br> +void <span style="font-weight: bold;">glTexParameterf</span>(GLenum<span + style="font-style: italic;"> target</span>, GLenum <span + style="font-style: italic;">pname</span>, GLfloat <span + style="font-style: italic;">value</span>)<br> +<br> +</div> +<span style="font-style: italic;">target</span> must be GL_TEXTURE_2D. + If <span style="font-style: italic;">pname</span> is +GL_TEXTURE_WRAP_S or GL_TEXTURE_WRAP_T then <span + style="font-style: italic;">value</span> must be either +GL_CLAMP_TO_EDGE or GL_REPEAT.<br> +<br> +For GL_CLAMP_TO_EDGE, texture coordinates are effectively clamped to +the interval [0, 1].<br> +<br> +For GL_REPEAT, the integer part of texture coordinates is ignored; only +the fractional part of the texture coordinates is used. This +allows texture images to repeated or tiled across an object.<br> +<br> +<h3>5.3.2 Texture Minification</h3> +The texture minification filter is set with the <span + style="font-weight: bold;">glTexParameteri </span>and<span + style="font-style: italic;"> </span><span style="font-weight: bold;">glTexParameterf</span><span + style="font-style: italic;"></span> commands by setting <span + style="font-style: italic;">target</span> to GL_TEXTURE_2D, setting <span + style="font-style: italic;">pname</span> to GL_TEXTURE_MIN_FILTER and +setting <span style="font-style: italic;">value</span> to GL_NEAREST, +GL_LINEAR, GL_NEAREST_MIPMAP_NEAREST, +GL_NEAREST_MIPMAP_LINEAR, GL_LINEAR_MIPMAP_NEAREST, or +GL_LINEAR_MIPMAP_LINEAR.<br> +<br> +GL_NEAREST samples the texel nearest the texture coordinate in the +level 0 texture image.<br> +<br> +GL_LINEAR samples the four texels around the texture coordinate in the +level 0 texture image. The four texels are linearly weighted to +compute the final texel value.<br> +<br> +GL_NEAREST_MIPMAP_NEAREST samples the texel nearest the texture +coordinate in the level N texture image. N is the level of detail +and is computed by the partial derivatives of the texture coordinates +with respect to the window coordinates.<br> +<br> +GL_NEAREST_MIPMAP_LINEAR samples two texels nearest the texture +coordinates in the level N and N+1 texture images. The two texels +are linearly weighted to compute the final texel value. N is the +level of detail and is computed by the partial derivatives of the +texture coordinates with respect to the window coordinates.<br> +<br> +GL_LINEAR_MIPMAP_NEAREST samples four texels around the texture +coordinate in the level N texture image. The four texels are +linearly weighted to compute the final texel value. N is the level +of detail and is computed by the partial derivatives of the texture +coordinates with respect to the window coordinates.<br> +<br> +GL_LINEAR_MIPMAP_LINEAR samples four texels around the texture +coordinate in the level N texture image and four texels around the +texture coordinate in the level N+1 texture image. The eight +texels are linearly weighted to compute the final texel value. N +is the level of detail and is computed by the partial derivatives of the +texture coordinates with respect to the window coordinates.<br> +<br> +Filter modes other than GL_LINEAR and GL_NEAREST requires that the +texture have a complete set of mipmaps. If the mipmap is +incomplete, it is as if texturing is disabled.<br> + <br> +<h3>5.3.3 Texture Magnification</h3> +The texture magnification filter is set with the <span + style="font-weight: bold;">glTexParameteri </span>and<span + style="font-style: italic;"> </span><span style="font-weight: bold;">glTexParameterf</span><span + style="font-style: italic;"></span> commands by setting <span + style="font-style: italic;">target</span> to GL_TEXTURE_2D, setting <span + style="font-style: italic;">pname</span> to GL_TEXTURE_MAG_FILTER and +setting <span style="font-style: italic;">value</span> to GL_NEAREST or +GL_LINEAR.<br> +<br> +GL_NEAREST samples the texel nearest the texture coordinate in the +level 0 texture image.<br> +<br> +GL_LINEAR samples the four texels around the texture coordinate in the +level 0 texture image. The four texels are linearly weighted to +compute the final texel value.<br> +<br> +If the texture minification filter is different than the texture +magnification filter, a level of detail value (lambda) is computed for +each fragment. The level of detail value determines if the texture +is being minified (multiple texels map to a single screen pixel) or +magnified (a single texel maps to multiple screen pixels). Lamda +is used to compute N (the texture level) for texture minification.<br> +<br> +<h2>5.4 Texture Application</h2> +The sampled texture values are combined with the incoming fragment +colors to produce a new fragment color. The fragment and texture +colors are combined according to the texture environment mode and the +current texture's base internal format. The texture environment +mode is set with the command<br> +<br> +<div style="margin-left: 40px;">void<span style="font-weight: bold;"> +glTexEnvi</span>(GLenum <span style="font-style: italic;">target</span>, +GLenum <span style="font-style: italic;">pname</span>, GLint <span + style="font-style: italic;">value</span>)<br> +</div> +<br> +<span style="font-style: italic;">target</span> must be GL_TEXTURE_ENV. + If <span style="font-style: italic;">pname</span> is +GL_TEXTURE_ENV_MODE then <span style="font-style: italic;">value</span> +must be one of GL_REPLACE, GL_MODULATE, GL_DECAL, or GL_BLEND.<br> +<br> +There is also a <span style="font-style: italic;">texture environment +color</span> that can factor into texture application. The texture +environment color can be set with the command<br> +<br> +<div style="margin-left: 40px;">void<span style="font-weight: bold;"> +glTexEnvfv</span>(GLenum <span style="font-style: italic;">target</span>, +GLenum <span style="font-style: italic;">pname</span>, const GLfloat *<span + style="font-style: italic;">value</span>)<br> +</div> +<span style="font-style: italic;"></span><br> +<span style="font-style: italic;">target</span> must be GL_TEXTURE_ENV. + If <span style="font-style: italic;">pname</span> is +GL_TEXTURE_ENV_COLOR then <span style="font-style: italic;">value </span>must +point to an array of four values which specify the red, green, blue, +and alpha values of the texture environment color. The values are +clamped to the range [0, 1]. The default color is (0, 0, 0, 0).<br> +<span style="font-style: italic;"></span><br> +The following table describes the arithmetic used for each combination +of environment mode and base internal format. (Rf, Gf, Bf, Af) is +the incoming fragment color. (Rt, Gt, Bt, At) is the sampled +texture color. Lt is the sampled texture luminance. <span + style="font-style: italic;"></span>'It' is the sampled texture +intensity. (Rc, Gc, Bc, Ac) is the texture environment color. + (Rv, Gv, Bv, Av) is the resulting value.<br> +<br> +<br> +<table cellpadding="2" cellspacing="2" border="1" + style="text-align: left; width: 90%; margin-left: auto; margin-right: auto;"> + <tbody> + <tr> + <td style="vertical-align: top;">Base Internal Format<br> + </td> + <td style="vertical-align: top;">GL_REPLACE<br> + </td> + <td style="vertical-align: top;">GL_MODULATE<br> + </td> + <td style="vertical-align: top;">GL_DECAL<br> + </td> + <td style="vertical-align: top;">GL_BLEND<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ALPHA<br> + </td> + <td style="vertical-align: top;">Rv = Rf<br> +Gv = Gf<br> +Bfv= Bf<br> +Av = At<br> + </td> + <td style="vertical-align: top;">Rv = Rf<br> +Gv = Gf<br> +Bv = Bf<br> +Av = Af * At<br> + </td> + <td style="vertical-align: top;">undefined<br> + </td> + <td style="vertical-align: top;">Rv = Rf<br> +Gv = Gf<br> +Bv = Bf<br> +Av = Af * At</td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LUMINANCE<br> + </td> + <td style="vertical-align: top;">Rv = Lt<br> +Gv = Lt<br> +Bv = Lt<br> +Av = Af<br> + </td> + <td style="vertical-align: top;">Rv = Rf * Lt<br> +Gv = Gf * Lt<br> +Bv = Bf * Lt<br> +Av = Af<br> + </td> + <td style="vertical-align: top;">undefined<br> + </td> + <td style="vertical-align: top;">Rv = Rf*(1-Lt) + Rc*Lt<br> +Gv = Gf*(1-Lt) + Gc*Lt<br> +Bv = Bf*(1-Lt) + Bc*Lt<br> +Av = Af</td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LUMINANCE_ALPHA<br> + </td> + <td style="vertical-align: top;">Rv = Lt<br> +Gv = Lt<br> +Bv = Lt<br> +Av = At<br> + </td> + <td style="vertical-align: top;">Rv = Rf * Lt<br> +Gv = Gf * Lt<br> +Bv = Bf * Lt<br> +Av = Af * At</td> + <td style="vertical-align: top;">undefined<br> + </td> + <td style="vertical-align: top;">Rv = Rf*(1-Lt) + Rc*Lt<br> +Gv = Gf*(1-Lt) + Gc*Lt<br> +Bv = Bf*(1-Lt) + Bc*Lt<br> +Av = Af*At</td> + </tr> + <tr> + <td style="vertical-align: top;">GL_INTENSITY<br> + </td> + <td style="vertical-align: top;">Rv = It<br> +Gv = It<br> +Bv = It<br> +Bf = It<br> + </td> + <td style="vertical-align: top;">Rv = Rf * It<br> +Gv = Gf * It<br> +Bv = Bf * It<br> +Av = Af * It</td> + <td style="vertical-align: top;">undefined<br> + </td> + <td style="vertical-align: top;">Rv = Rf*(1-It) + Rc*It<br> +Gv = Gf*(1-It) + Gc*It<br> +Bv = Bf*(1-It) + Bc*It<br> +Av = Af*(1-It) + Ac*It</td> + </tr> + <tr> + <td style="vertical-align: top;">GL_RGB<br> + </td> + <td style="vertical-align: top;">Rv = Rt<br> +Gv = Gt<br> +Bv = Bt<br> +Av = Af<br> + </td> + <td style="vertical-align: top;">Rv = Rf * Rt<br> +Gv = Gf * Gt<br> +Bv = Bf * Bt<br> +Av = Af<br> + </td> + <td style="vertical-align: top;">Rv = Rt<br> +Gv = Gt<br> +Bv = Bt<br> +Av = Af</td> + <td style="vertical-align: top;">Rv = Rf*(1-Rt) + Rc*Rt<br> +Gv = Gf*(1-Gt) + Gc*Gt<br> +Bv = Bf*(1-Bt) + Bc*Bt<br> +Av = Af</td> + </tr> + <tr> + <td style="vertical-align: top;">GL_RGBA<br> + </td> + <td style="vertical-align: top;">Rv = Rt<br> +Gv = Gt<br> +Bv = Bt<br> +Av = At<br> + </td> + <td style="vertical-align: top;">Rv = Rf * Rt<br> +Gv = Gf * Gt<br> +Bv = Bf * Bt<br> +Av = Af * At</td> + <td style="vertical-align: top;">Rv = Rf*(1-At) + Rt*At<br> +Gv = Gf*(1-At) + Gt*At<br> +Bv = Bf*(1-At) + Bt*At<br> +Av = Af<br> + </td> + <td style="vertical-align: top;">Rv = Rf*(1-Rt) + Rc*Rt<br> +Gv = Gf*(1-Gt) + Gc*Gt<br> +Bv = Bf*(1-Bt) + Bc*Bt<br> +Av = Af*At</td> + </tr> + </tbody> +</table> +<br> +<br> +2D texture mapping is enabled and disabled with the commands <span + style="font-weight: bold;">glEnable</span>(GL_TEXTURE_2D) and <span + style="font-weight: bold;">glDisable</span>(GL_TEXTURE_2D).<br> +<br> +<br> +<h2>5.5 Texture Objects</h2> +Texture objects encapsulate a set of texture images (mipmap) and +related state into a named object. This facilitates use of +multiple textures in an application. Texture objects are named +with GLuints (unsigned integers). There is a default texture +object with the name/identifier zero which can never be deleted.<br> +<br> +<h3>5.5.1 Creating Texture Objects</h3> +A texture object is created by binding a new GLuint identifier to the +GL_TEXTURE_2D target with the command:<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glBindTexture</span>(GLenum<span + style="font-style: italic;">target</span>, GLuint <span + style="font-style: italic;">textureID</span>)<br> +</div> +<br> +<span style="font-style: italic;">target</span> must be GL_TEXTURE_2D. + <span style="font-style: italic;">textureID</span> may be any +unsigned integer. If <span style="font-style: italic;">textureID</span> +does not name an existing texture object, a new texture object with that +ID will be created, initialized to the default state. Whether the +ID is new or existed previously, that named texture object is bound as +the <span style="font-style: italic;">current texture object</span>. + Subsequent <span style="font-weight: bold;">glTexParameter </span>and<span + style="font-weight: bold;">glTexImage2D<span + style="font-style: italic;"> </span></span>calls will effect the +current texture object.<br> +<span style="font-style: italic;"></span><span + style="font-weight: bold;"><span style="font-style: italic;"> </span></span><br> +<h3>5.5.2 Deleting Texture Objects</h3> +One or more texture objects may be deleted with the command:<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glDeleteTextures</span>(GLsizei<span + style="font-style: italic;">n</span>, const GLuint *<span + style="font-style: italic;">textureIDs</span>)<br> +</div> +<br> +<span style="font-style: italic;">textureIDs</span> is an array of <span + style="font-style: italic;">n</span> texture IDs. The named +texture objects will be deleted. If the current texture object is +deleted the default texture object (with ID 0) will be bound as the +current texture object.<br> +<br> +<h3>5.5.3 Allocating Texture Object Identifiers</h3> +A list of new, unused texture IDs can be obtained by calling the command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glGenTextures</span>(GLsizei<span + style="font-style: italic;">n</span>, GLuint *<span + style="font-style: italic;">textureIDs</span>)<br> +</div> +<br> +An array of <span style="font-style: italic;">n</span> unused texture +IDs will be returned in the <span style="font-style: italic;">textureIDs</span> +array.<br> +<br> +<h3>5.5.4 Texture Residency</h3> +Since hardware texture memory is usually a scarce resource, not all +textures may be resident in hardware memory at a given time. The +command<br> +<br> +<div style="margin-left: 40px;">GLboolean <span + style="font-weight: bold;">glAreTexturesResident</span>(GLsizei <span + style="font-style: italic;">n</span>, const GLuint *<span + style="font-style: italic;">textureIDs</span>, GLboolean *<span + style="font-style: italic;">residences</span>)<br> +</div> +<br> +can be used to query whether or not a set of textures are currently +resident in hardware memory. The <span style="font-style: italic;">textureIDs</span> +array contains <span style="font-style: italic;">n</span> texture IDs. + If one or more textures are not resident, then GL_FALSE will be +returned and the <span style="font-style: italic;">residences</span> +array will return <span style="font-style: italic;">n</span> GL_TRUE or +GL_FALSE values to indicate if the corresponding texture is resident or +not resident, respectively. Otherwise, if all the textures are +resident, GL_TRUE will be returned and the <span + style="font-style: italic;">residences</span> array will be unchanged.<br> +<br> +The user can influence the system's determination of which textures +should be resident when hardware texture memory is overcomitted by +assigning priorities to texture objects. Priorities are set with +the command:<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glPrioritizeTexture</span>(GLsizei<span + style="font-style: italic;">n</span>, const GLuint *<span + style="font-style: italic;">textureIDs</span>, const GLclampf *<span + style="font-style: italic;">priorities</span>)<br> +</div> +<br> +The <span style="font-style: italic;"><span style="font-style: italic;"></span>textureIDs</span> +array and <span style="font-style: italic;">priorities</span> array +contain a list of <span style="font-style: italic;">n</span> texture +object IDs and desired priorities for those texture objects. Each +priority is clamped to the range [0, 1]. Zero indicates lowest +priority and one indicates highest priority. Attempting to set the +priority of texture object zero (the defaulte texture object) will be +ignored. The priority for the currently bound texture object may +also be set with the <span style="font-weight: bold;">glTexParameter</span> +function if <span style="font-style: italic;">target</span> is set to +GL_TEXTURE_2D and <span style="font-style: italic;">pname</span> is set +to GL_TEXTURE_PRIORITY and <span style="font-style: italic;">value</span> +is the priority.<br> +<br> +<br> +<h1>6. Per-fragment Operations</h1> +The fragments produced by rasterization are subjected to a number of +operations which either modify the fragment or test the fragment +(discarding the fragment if the test fails.) This chapter +describes the per-fragment operations. They are presented in the +order in which they're performed. If a fragment fails a test it is +discarded and not subjected to subsequent tests or modifications.<br> +<br> +<h2>6.1 Scissor Test</h2> +The scissor test limits rendering to a 2-D rectangular region of the +framebuffer. The command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glScissor</span>(GLint<span + style="font-style: italic;">x</span>, GLint <span + style="font-style: italic;">y</span>, GLsizei <span + style="font-style: italic;">width</span>, GLsizei<span + style="font-style: italic;"> height</span>)<br> +</div> +<br> +defines a clipping region with the lower-left corner at (<span + style="font-style: italic;">x, y</span>) and the given <span + style="font-style: italic;">width</span> and <span + style="font-style: italic;">height</span>. The scissor test is +enabled and disabled with the command <span style="font-weight: bold;">glEnable</span>(GL_SCISSOR_TEST) +and <span style="font-weight: bold;">glDisable</span>(GL_SCISSOR_TEST).<br> +<br> +If the incoming fragment's position is (x<sub>f</sub>, y<sub>f</sub>) +then the fragment will pass the test if <span + style="font-style: italic;">x</span> <= x<sub>f</sub> < <span + style="font-style: italic;">x</span> + <span + style="font-style: italic;">width</span> and <span + style="font-style: italic;">y</span> <= y<sub>f</sub> < <span + style="font-style: italic;">y</span> + <span + style="font-style: italic;">height. </span>Otherwise, the +fragment is discarded.<br> +<br> +If <span style="font-style: italic;">width</span> or <span + style="font-style: italic;">height</span> is less than zero the error +GL_INVALID_VALUE is raised. The default scissor rectangle bounds +are (0, 0, w, h) where w is the initial window width and h is the +initial window height. The scissor test is disabled by default.<br> +<br> +<h2>6.2 Alpha Test</h2> +The alpha test compares the fragment's alpha value against a reference +value and discards the fragment if the comparison fails. The test +is specified by the command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glAlphaFunc</span>(GLenum<span + style="font-style: italic;">mode</span>, GLclampf <span + style="font-style: italic;">reference</span>)<br> +</div> +<br> +<span style="font-style: italic;">mode</span> specifies an inequality +and <span style="font-style: italic;">reference</span> specifies a value +to compare against. The following table lists all possible +modes <span style="font-style: italic;"></span>and the +corresponding test:<br> +<br> +<table cellpadding="2" cellspacing="2" border="1" + style="text-align: left; width: 50%; margin-left: auto; margin-right: auto;"> + <tbody> + <tr> + <td style="vertical-align: top;">Comparison mode<br> + </td> + <td style="vertical-align: top;">The test passes if<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LESS<br> + </td> + <td style="vertical-align: top;">alpha < <span + style="font-style: italic;">reference</span><br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LEQUAL<br> + </td> + <td style="vertical-align: top;">alpha <= <span + style="font-style: italic;">reference</span></td> + </tr> + <tr> + <td style="vertical-align: top;">GL_GREATER<br> + </td> + <td style="vertical-align: top;">alpha > <span + style="font-style: italic;">reference</span></td> + </tr> + <tr> + <td style="vertical-align: top;">GL_GEQUAL<br> + </td> + <td style="vertical-align: top;">alpha >= <span + style="font-style: italic;">reference</span></td> + </tr> + <tr> + <td style="vertical-align: top;">GL_EQUAL<br> + </td> + <td style="vertical-align: top;">alpha == <span + style="font-style: italic;">reference</span></td> + </tr> + <tr> + <td style="vertical-align: top;">GL_NOTEQUAL<br> + </td> + <td style="vertical-align: top;">alpha != <span + style="font-style: italic;">reference</span></td> + </tr> + <tr> + <td style="vertical-align: top;">GL_NEVER<br> + </td> + <td style="vertical-align: top;">never pass<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ALWAYS<br> + </td> + <td style="vertical-align: top;">always passes<br> + </td> + </tr> + </tbody> +</table> +<br> +The <span style="font-style: italic;">reference</span> parameter is +clamped to the range [0, 1].<br> +<br> +The alpha test is enabled and disabled with the commands <span + style="font-weight: bold;">glEnable</span>(GL_ALPHA_TEST) and <span + style="font-weight: bold;">glDisable</span>(GL_ALPHA_TEST).<br> +<br> +The default mode is GL_ALWAYS and the default reference value is 0.<br> +<br> +<h2>6.3 Stencil Test</h2> +The stencil buffer stores an N-bit integer value for each pixel in the +frame buffer. The stencil test compares the stencil buffer value +at the fragment's position to a reference value and possibly discards +the fragment based on the outcome. Furthermore, the stencil buffer +value may be updated or modified depending on the outcome. If +there is no stencil buffer the stencil test is bypassed.<br> +<br> +Stenciling is controlled by the commands<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glStencilFunc</span>(GLenum<span + style="font-style: italic;">func</span>, GLint <span + style="font-style: italic;">ref</span>, GLuint <span + style="font-style: italic;">mask</span>)<br> +void <span style="font-weight: bold;">glStencilOp</span>(GLenum <span + style="font-style: italic;">stencilFail</span>, GLenum <span + style="font-style: italic;">depthTestFail</span>, GLenum <span + style="font-style: italic;">depthTestPass</span>)<br> +</div> +<br> +The <span style="font-weight: bold;">glStencilFunc<span + style="font-style: italic;"> </span></span>command controls the +stencil test while <span style="font-weight: bold;">glStencilOp</span> +command controls the how the stencil buffer is updated/modified after +the test.<br> +<br> +<span style="font-style: italic;">ref</span> is clamped to the range [0, +2<sup>N</sup>-1] where N is the number of bits per stencil value in the +stencil buffer.<span style="font-style: italic;"></span><br> +<br> +The following table lists all possible values for the <span + style="font-style: italic;">func</span> parameter and when the stencil +test will pass. Both the stencil buffer value and the stencil +reference value are bit-wise ANDed with the <span + style="font-style: italic;">mask</span> parameter before the test.<br> +<br> +<span style="font-style: italic;"></span><span + style="font-style: italic;"></span><span style="font-style: italic;"></span> +<table + style="text-align: left; margin-left: auto; margin-right: auto; width: 70%;" + border="1" cellspacing="2" cellpadding="2"> + <tbody> + <tr> + <td style="vertical-align: top;">Stencil <span + style="font-style: italic;">func</span> value<br> + </td> + <td style="vertical-align: top;">Stencil test passes if<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LESS<br> + </td> + <td style="vertical-align: top;"><span style="font-style: italic;">(ref</span>&<span + style="font-style: italic;">mask)</span> < (stencil buffer value +& <span style="font-style: italic;">mask)</span><br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LEQUAL<br> + </td> + <td style="vertical-align: top;"><span style="font-style: italic;">(ref</span> +& <span style="font-style: italic;">mask) </span><= (stencil +buffer value & <span style="font-style: italic;">mask)</span></td> + </tr> + <tr> + <td style="vertical-align: top;">GL_GREATER<br> + </td> + <td style="vertical-align: top;"><span style="font-style: italic;">(ref</span> +& <span style="font-style: italic;">mask) </span>> (stencil +buffer value & <span style="font-style: italic;">mask)</span></td> + </tr> + <tr> + <td style="vertical-align: top;">GL_GEQUAL<br> + </td> + <td style="vertical-align: top;"><span style="font-style: italic;">(ref</span> +& <span style="font-style: italic;">mask) </span>>= (stencil +buffer value & <span style="font-style: italic;">mask)</span></td> + </tr> + <tr> + <td style="vertical-align: top;">GL_EQUAL<br> + </td> + <td style="vertical-align: top;"><span style="font-style: italic;">(ref</span> +& <span style="font-style: italic;">mask) </span>== (stencil +buffer value & <span style="font-style: italic;">mask)</span></td> + </tr> + <tr> + <td style="vertical-align: top;">GL_NOTEQUAL<br> + </td> + <td style="vertical-align: top;"><span style="font-style: italic;">(ref</span> +& <span style="font-style: italic;">mask) </span>!= (stencil +buffer value & <span style="font-style: italic;">mask)</span></td> + </tr> + <tr> + <td style="vertical-align: top;">GL_NEVER<br> + </td> + <td style="vertical-align: top;">never passes<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ALWAYS<br> + </td> + <td style="vertical-align: top;">always passes<br> + </td> + </tr> + </tbody> +</table> +<br> +<span style="font-style: italic;"></span><br> +If the stencil test passes, the fragment is passed to the next +per-fragment operation. Otherwise, if the stencil test fails, the +value in the stencil buffer is updated according to the value of the <span + style="font-style: italic;">stencilFail</span> parameter to <span + style="font-weight: bold;">glStencilOp</span>.<br> +<br> +<table cellpadding="2" cellspacing="2" border="1" + style="text-align: left; width: 70%; margin-left: auto; margin-right: auto;"> + <tbody> + <tr> + <td style="vertical-align: top;"><span style="font-style: italic;">stencilFail</span> +value<br> + </td> + <td style="vertical-align: top;">New stencil buffer value<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_KEEP<br> + </td> + <td style="vertical-align: top;">originalValue<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ZERO<br> + </td> + <td style="vertical-align: top;">0<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_INVERT<br> + </td> + <td style="vertical-align: top;">BitWiseInvert(originalValue) +i.e. ~originalValue<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_REPLACE<br> + </td> + <td style="vertical-align: top;"><span style="font-style: italic;">ref</span><br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_INCR<br> + </td> + <td style="vertical-align: top;">originalValue + 1, clamped to +[0, 2<sup>N</sup>-1]</td> + </tr> + <tr> + <td style="vertical-align: top;">GL_DECR<br> + </td> + <td style="vertical-align: top;">originalValue - 1, clamped to +[0, 2<sup>N</sup>-1]</td> + </tr> + </tbody> +</table> +<span style="font-style: italic;"></span><span + style="font-style: italic;"></span><br> +<br> +The <span style="font-style: italic;">depthTestFail</span> and <span + style="font-style: italic;">depthTestPass</span> parameters to <span + style="font-weight: bold;">glStencilOp</span> are ignored. Values +for <span style="font-style: italic;">func</span> and <span + style="font-style: italic;">stencilFail</span> other than those listed +in the table will cause the error GL_INVALID_ENUM to be raised.<br> +<br> +The stencil test is enabled and disabled with the commands <span + style="font-weight: bold;">glEnable</span>(GL_STENCIL_TEST) and <span + style="font-weight: bold;">glDisable</span>(GL_STENCIL_TEST).<br> +<br> +The default stencil function is GL_ALWAYS. The default stencil +reference value is 0. The default stencil mask is ~0. The +default stencil fail operation is GL_KEEP.<br> +<br> +Values written into the stencil buffer are masked with the command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glStencilMask</span>(GLuint<span + style="font-style: italic;">mask</span>)<br> +</div> +<br> +Only the bits which are set in <span style="font-style: italic;">mask</span> +will be modified in the stencil buffer when written to. If each +stencil buffer value has N bits, only the least significant N bits of <span + style="font-style: italic;">mask</span> are relevant. The default +stencil mask is ~0.<br> +<br> +<h2>6.4 Blending and Logicop</h2> +Blending or a logic operation combines the incoming fragment color with +the destination frame buffer color according to a blending equation or +bit-wise Boolean logical operation.<br> +<br> +Blending is enabled and disabled with the commands <span + style="font-weight: bold;">glEnable</span>(GL_BLEND) and <span + style="font-weight: bold;">glDisable</span>(GL_BLEND).<br> +<br> +The logic operation is enabled and disabled with the commands <span + style="font-weight: bold;">glEnable</span>(GL_LOGIC_OP) and <span + style="font-weight: bold;">glDisable</span>(GL_LOGIC_OP).<br> +<br> +If both blending and the logic operation are enabled, the logic +operation has higher priority; blending is bypassed.<br> +<br> +<h3>6.4.1 Logic Op</h3> +The command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glLogicop</span>(GLenum<span + style="font-style: italic;">mode</span>)<br> +<br> +</div> +Specifies the Boolean logic operation for combining the incoming +fragment color with the destination frame buffer color. Both the +incoming fragment color and destination frame buffer colors are +interpreted as four-tuples of unsigned integer color components in the +range [0, 2<sup>N</sup>-1] where N is the number of bits per color +channel. N may not be the same for all color channels.<br> +<br> +The following table lists all values for <span + style="font-style: italic;">mode</span> and the boolean arithmetic used +to combine the incoming fragment color value (src)<span + style="font-style: italic;"></span><span style="font-style: italic;"></span><span + style="font-style: italic;"></span><span style="font-style: italic;"></span><span + style="font-style: italic;"></span> with the destination framebuffer +color value (dst). Standard ANSI C operators used.<br> +<br> +<table cellpadding="2" cellspacing="2" border="1" + style="text-align: left; width: 50%; margin-left: auto; margin-right: auto;"> + <tbody> + <tr> + <td style="vertical-align: top;">LogicOp <span + style="font-style: italic;">mode</span><br> + </td> + <td style="vertical-align: top;">Resulting channel value<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_CLEAR<br> + </td> + <td style="vertical-align: top;">0<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_SET<br> + </td> + <td style="vertical-align: top;">~0<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_COPY<br> + </td> + <td style="vertical-align: top;">src<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_COPY_INVERTED<br> + </td> + <td style="vertical-align: top;">~s<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_NOOP<br> + </td> + <td style="vertical-align: top;">dst<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_INVERT<br> + </td> + <td style="vertical-align: top;">~dst<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_AND<br> + </td> + <td style="vertical-align: top;">src & dst<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_NAND<br> + </td> + <td style="vertical-align: top;">~(src & dst)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_AND_REVERSE<br> + </td> + <td style="vertical-align: top;">src & ~dst<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_AND_INVERTED<br> + </td> + <td style="vertical-align: top;">~src & dst<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_OR<br> + </td> + <td style="vertical-align: top;">src | dst<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_NOR<br> + </td> + <td style="vertical-align: top;">~(src | dst)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_OR_REVERSE<br> + </td> + <td style="vertical-align: top;">src | ~dst<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_OR_INVERTED<br> + </td> + <td style="vertical-align: top;">~src | dst<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_XOR<br> + </td> + <td style="vertical-align: top;">src ^ dst<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_EQUIV<br> + </td> + <td style="vertical-align: top;">~(src ^ dst)<br> + </td> + </tr> + </tbody> +</table> +<br> +The fragment's color is replaced by the result of the logic operation.<br> +<br> +Specifying any value for <span style="font-style: italic;">mode</span> +other than those listed in the above table will cause the error +GL_INVALID_ENUM to be raised.<br> +<br> +The default value for <span style="font-style: italic;">mode</span> is +GL_COPY. The logic operation is disabled by default.<br> +<br> +<h3>6.4.2 Blending</h3> +The command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glBlendFunc</span>(GLenum<span + style="font-style: italic;">srcTerm</span>, GLenum <span + style="font-style: italic;">dstTerm</span>)<br> +</div> +<br> +specifies the terms of the blending equation. If Cf = (Rf, Gf, +Bf, Af) is the incoming fragment color and Cb = (Rb, Gb, Bb, Ab) is the +frame buffer color, then the resulting color Cv = (Rv, Gv, Bv, Av) is +computed by:<br> +<br> +<div style="margin-left: 40px;">Cv = Cf * <span + style="font-style: italic;">srcTerm</span> + Cb * <span + style="font-style: italic;">dstTerm</span><br> +<span style="font-style: italic;"></span></div> +<span style="font-style: italic;"> </span><br> +All possible values for <span style="font-style: italic;">srcTerm</span> +and the corresponding arithmetic term are listed in the following table:<br> +<br> +<table cellpadding="2" cellspacing="2" border="1" + style="text-align: left; width: 70%; margin-left: auto; margin-right: auto;"> + <tbody> + <tr> + <td style="vertical-align: top;"><span style="font-style: italic;">srcTerm</span><br> + </td> + <td style="vertical-align: top;"><span style="font-style: italic;">srcTerm</span>Arithmetic<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ZERO<br> + </td> + <td style="vertical-align: top;">(0, 0, 0, 0)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ONE<br> + </td> + <td style="vertical-align: top;">(1, 1, 1, 1)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_DST_COLOR<br> + </td> + <td style="vertical-align: top;">(Rb, Gb, Bb, Ab)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ONE_MINUS_DST_COLOR<br> + </td> + <td style="vertical-align: top;">(1-Rb, 1-Gb, 1-Bb, 1-Ab)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_SRC_ALPHA<br> + </td> + <td style="vertical-align: top;">(Af, Af, Af, AF)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ONE_MINUS_SRC_ALPHA<br> + </td> + <td style="vertical-align: top;">(1-Af, 1-Af, 1-Af, 1-Af)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_DST_ALPHA<br> + </td> + <td style="vertical-align: top;">(Ab, Ab, Ab, Ab)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ONE_MINUS_DST_ALPHA<br> + </td> + <td style="vertical-align: top;">(1-Ab, 1-Ab, 1-Ab, 1-Ab)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_SRC_ALPHA_SATURATE<br> + </td> + <td style="vertical-align: top;">(m, m, m, 1) where m = MIN(Af, +1-Ab)<br> + </td> + </tr> + </tbody> +</table> +<br> +All possible values for <span style="font-style: italic;">srcTerm</span> +and the corresponding arithmetic term are listed in the following table:<br> +<br> +<table cellpadding="2" cellspacing="2" border="1" + style="text-align: left; width: 70%; margin-left: auto; margin-right: auto;"> + <tbody> + <tr> + <td style="vertical-align: top;"><span style="font-style: italic;">dstTerm</span><br> + </td> + <td style="vertical-align: top;"><span style="font-style: italic;">dstTerm</span>Arithmetic<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ZERO<br> + </td> + <td style="vertical-align: top;">(0, 0, 0, 0)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ONE<br> + </td> + <td style="vertical-align: top;">(1, 1, 1, 1)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_SRC_COLOR<br> + </td> + <td style="vertical-align: top;">(Rf, Gf, Bf, Af)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ONE_MINUS_SRC_COLOR<br> + </td> + <td style="vertical-align: top;">(1-Rf, 1-Gf, 1-Bf, 1-Af)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_SRC_ALPHA<br> + </td> + <td style="vertical-align: top;">(Af, Af, Af, AF)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ONE_MINUS_SRC_ALPHA<br> + </td> + <td style="vertical-align: top;">(1-Af, 1-Af, 1-Af, 1-Af)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_DST_ALPHA<br> + </td> + <td style="vertical-align: top;">(Ab, Ab, Ab, Ab)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ONE_MINUS_DST_ALPHA<br> + </td> + <td style="vertical-align: top;">(1-Ab, 1-Ab, 1-Ab, 1-Ab)<br> + </td> + </tr> + </tbody> +</table> +<br> +The fragment's color is replaced by the result of the blending equation.<br> +<br> +Values for <span style="font-style: italic;">srcTerm</span> and <span + style="font-style: italic;">dstTerm</span> other than those listed in +the table will cause the error GL_INVALID_ENUM to be raised.<br> +<br> +The default value for <span style="font-style: italic;">srcTerm</span> +is GL_ONE. The default value for <span style="font-style: italic;">dstTerm</span> +is GL_ZERO. Blending is disabled by default.<br> +<br> +<h2>6.5 Color Mask</h2> +The final fragment color is written into the current color buffer at +the end of the per-fragment operations. Normally, all color +channels in the frame buffer are replaced with the final fragment color. + However, the command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glColorMask</span>(GLboolean<span + style="font-style: italic;">redMask</span>, GLboolean <span + style="font-style: italic;">greenMask</span>, GLboolean <span + style="font-style: italic;">blueMask</span>, GLboolena <span + style="font-style: italic;">alphaMask</span>)<br> +</div> +<br> +allows selective writting to individual color channels. If <span + style="font-style: italic;">redMask</span> is GL_TRUE then writing to +the red color channel is enabled, otherwise it's disabled. + Similarly, the green, blue and alpha channels can also be masked.<br> +<br> +Initially all four mask values are GL_TRUE.<br> +<br> +Color masking is not enabled/disabled with the <span + style="font-weight: bold;">glEnable</span>/<span + style="font-weight: bold;">glDisable</span> commands.<br> +<br> +<h1>7. Frame Buffer Operations</h1> +The frame buffer is considered to be a two-dimensional array of pixels. + The frame buffer is also organized into layers or logical buffers. + There may be a front color buffer, back color buffer and stencil +buffer. A double-buffered frame buffer has both a front color +buffer and back color buffer. A single-buffered framebuffer only +has a front color buffer. Each pixel in a color buffer has a red, +green and blue value and an optional alpha value.<br> +<br> +<h2>7.1 Clearing Buffers</h2> +Buffers are cleared (set to uniform values) with the command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glClear</span>(GLbitfield<span + style="font-style: italic;">buffers</span>)<br> +</div> +<br> +<span style="font-style: italic;">buffers</span> is a bitmask for which +the value may be the bitwise-OR of the values GL_COLOR_BUFFER_BIT and +GL_STENCIL_BUFFER_BIT. If the GL_COLOR_BUFFER_BIT bit is +specified, the current color buffer will be cleared. If the +GL_STENCIL_BUFFER_BIT bit is specified, the stencil buffer will be +cleared.<br> +<br> +The current color buffer is specified with the command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glDrawBuffer</span>(GLenum<span + style="font-style: italic;"> buffer</span>)<br> +</div> +<br> +<span style="font-style: italic;">buffer</span> may be either GL_FRONT, +GL_BACK or GL_NONE. GL_FRONT indicates that the front color buffer +will be modified by <span style="font-weight: bold;">glClear</span> and +any drawing command. GL_BACK indicates that the back color buffer +will be modified by <span style="font-weight: bold;">glClear</span> and +any drawing command. GL_NONE indicates that neither color buffer +will be modified by <span style="font-weight: bold;">glClear</span> or +any drawing command. GL_BACK is only valid for double-buffered +frame buffers.<br> +<br> +The current scissor rectangle, set by the <span + style="font-weight: bold;">glScissor</span> command, effects <span + style="font-weight: bold;">glClear</span><span + style="font-style: italic;">,</span><span style="font-style: italic;"> </span>limiting +the clear to the scissor rectangle, if it's enabled. Furthermore, <span + style="font-weight: bold;"></span>only the color channels enabled by <span + style="font-weight: bold;">glColorMask</span> will be effected by <span + style="font-weight: bold;">glClear</span>(GL_COLOR_BUFFER_BIT). + Likewise, only the stencil bits enabled by <span + style="font-weight: bold;">glStencilMask</span> will be effected by <span + style="font-weight: bold;">glClear</span>(GL_STENCIL_BUFFER_BIT).<br> +<br> +The current clear color is set with the command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glClearColor</span>(GLclampf<span + style="font-style: italic;">red</span>, GLclampf <span + style="font-style: italic;">green</span>, GLclampf <span + style="font-style: italic;">blue</span>, GLclampf <span + style="font-style: italic;">alpha</span>)<br> +</div> +<br> +Subsequent calls to <span style="font-weight: bold;">glClear</span> +will use the color (<span style="font-style: italic;">red, green, blue, +alpha</span>) to clear the front or back color buffers.<br> +<span style="font-style: italic;"></span><br> +The current stencil clear value is set with the command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glClearStencil</span>(GLint<span + style="font-style: italic;">clearValue</span>)<br> +</div> +<br> +If the stencil buffer is N bits deep, the least significant N bits of <span + style="font-style: italic;">clearValue</span> will be used to clear the +stencil buffer.<br> +<br> +<br> +<h1>8. Other Features</h1> +<h2>8.1 Frame Buffer Readback</h2> +A rectangular region of pixels can be read from the frame buffer and +placed in client memory with the command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glReadPixels</span>(GLint<span + style="font-style: italic;">x</span>, GLint <span + style="font-style: italic;">y</span>, GLsizei <span + style="font-style: italic;">width</span>, GLsizei <span + style="font-style: italic;">height</span>, GLenum <span + style="font-style: italic;">format</span>, GLenum <span + style="font-style: italic;">type</span>, GLvoid *<span + style="font-style: italic;">data</span>)<br> +</div> +<br> +<span style="font-style: italic;">x</span> and <span + style="font-style: italic;">y</span> specify the coordinate of the +lower-left corner of the region to read and <span + style="font-style: italic;">width</span> and <span + style="font-style: italic;">height</span> specify the size of the +rectangular region to read. <span style="font-style: italic;">format</span> +specifies the format of image data and must be either GL_RGB or +GL_RGBA. <span style="font-style: italic;">type</span> specify the +data type of the image data and must be either GL_UNSIGNED_BYTE or +GL_FLOAT. Other values for <span style="font-style: italic;">format</span> +or <span style="font-style: italic;">type</span> will cause the error +GL_INVALID_ENUM to be raised.<br> +<br> +The framebuffer may contain 3-component colors (red, green, blue) or +4-component colors (red, green, blue, alpha). If an alpha channel +is not present, alpha values default to 1.0.<br> +<br> +The frame buffer color components (red, green, blue, alpha) are either +converted to 8-bit unsigned integers in the range[0, 255] if <span + style="font-style: italic;">type </span>is GL_UNSIGNED_BYTE or +converted to floating point values in the range [0, 1] if <span + style="font-style: italic;">type</span> is GL_FLOAT. The (red, +greeen, blue, alpha) tuples are then stored as GL_RGB triplets (by +dropping the alpha component) or GL_RGBA quadruples in client memory.<br> +<br> +Image data is <span style="font-style: italic;">packed</span> into +client memory according to the pixel packing parameters which may be set +by the command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glPixelStorei</span>(GLenum<span + style="font-style: italic;">pname</span>, GLint <span + style="font-style: italic;">value</span>)<br> +</div> +<br> +<span style="font-style: italic;">pname</span> may be one of the values +in the following table:<br> +<br> +<table cellpadding="2" cellspacing="2" border="1" + style="text-align: left; width: 90%; margin-left: auto; margin-right: auto;"> + <tbody> + <tr> + <td style="vertical-align: top;">Parameter (<span + style="font-style: italic;">pname</span>)<br> + </td> + <td style="vertical-align: top;">Value (<span + style="font-style: italic;">value</span>)<br> + </td> + <td style="vertical-align: top;">Default<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_PACK_ROW_LENGTH<br> + </td> + <td style="vertical-align: top;">Width of the image in memory, in +pixels.<br> + </td> + <td style="vertical-align: top;">0<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_PACK_SKIP_PIXELS<br> + </td> + <td style="vertical-align: top;">Number of pixels to skip +horizontally in each image row in memory.<br> + </td> + <td style="vertical-align: top;">0<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_PACK_SKIP_ROWS<br> + </td> + <td style="vertical-align: top;">Number of pixels to skip +vertically in the image in memory before unpacking.<br> + </td> + <td style="vertical-align: top;">0<br> + </td> + </tr> + </tbody> +</table> +<br> +These parameters allow the image to be stored within a sub-region of an +image buffer if desired. The following algorithm is used to pack +image data into client memory:<br> +<br> +<div style="margin-left: 40px;">if (GL_PACK_ROW_LENGTH == 0)<br> + rowLength = <span style="font-style: italic;">width</span>;<br> +else<br> + rowLength = GL_PACK_ROW_LENGTH<br> +<br> +if (<span style="font-style: italic;">format</span> == GL_RGB) {<br> + for (i = 0; i < <span style="font-style: italic;">height</span>; +i++) {<br> + for (j = 0; j < <span + style="font-style: italic;">width</span>; j++) {<br> + k = ((i + +GL_PACK_SKIP_ROWS) * rowLength + (j + GL_PACK_SKIP_PIXELS)) * 3;<br> + <span + style="font-style: italic;">data</span>[k+0] = FrameBuffer(<span + style="font-style: italic;">x</span> + j, <span + style="font-style: italic;">y</span> + i).red;<br> + <span + style="font-style: italic;">data</span>[k+1] = FrameBuffer(<span + style="font-style: italic;">x</span> + j, <span + style="font-style: italic;">y</span> + i).green;<br> + <span + style="font-style: italic;">data</span>[k+2] = FrameBuffer(<span + style="font-style: italic;">x</span> + j, <span + style="font-style: italic;">y</span> + i).blue;<span + style="font-style: italic;"></span><br> + }<br> + }<br> +}<br> +else {<br> + for (i = 0; i < <span style="font-style: italic;">height</span>; +i++) {<br> + for (j = 0; j < <span + style="font-style: italic;">width</span>; j++) {<br> + k = ((i + +GL_PACK_SKIP_ROWS) * rowLength + (j + GL_PACK_SKIP_PIXELS)) * 4;<br> + <span + style="font-style: italic;">data</span>[k+0] = FrameBuffer(<span + style="font-style: italic;">x</span> + j, <span + style="font-style: italic;">y</span> + i).red;<br> + <span + style="font-style: italic;">data</span>[k+1] = FrameBuffer(<span + style="font-style: italic;">x</span> + j, <span + style="font-style: italic;">y</span> + i).green;<br> + <span + style="font-style: italic;">data</span>[k+2] = FrameBuffer(<span + style="font-style: italic;">x</span> + j, <span + style="font-style: italic;">y</span> + i).blue;<span + style="font-style: italic;"></span><br> + <span + style="font-style: italic;">data</span>[k+3] = FrameBuffer(<span + style="font-style: italic;">x</span> + j, <span + style="font-style: italic;">y</span> + i).alpha;<span + style="font-style: italic;"></span><br> + }<br> + }<br> +}<br> +</div> +<br> +The function FrameBuffer(<span style="font-style: italic;">c, r</span>) +returns the pixel in the frame buffer at column <span + style="font-style: italic;">c</span> of row <span + style="font-style: italic;">r. </span><span + style="font-style: italic;">data</span> is considered to be either a +GLubyte pointer or a GLfloat pointer, depending on the <span + style="font-style: italic;">type</span> parameter. Similarly, the +FrameBuffer function returns either GLubyte values in the range [0, 255] +or GLfloat values in the range [0,1], depending on the <span + style="font-style: italic;">type</span> parameter.<br> +<br> +Pixels may be read from either the front or back color buffer. + The command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glReadBuffer</span>(GLenum<span + style="font-style: italic;">buffer</span>)<br> +</div> +<br> +specifies the source for reading images with <span + style="font-weight: bold;">glReadPixels</span>. If <span + style="font-style: italic;">buffer</span> is GL_FRONT then front color +buffer is the source. If <span style="font-style: italic;">buffer</span> +is GL_BACK then the back color buffer is the source. It is illegal +to specify GL_BACK when the color buffer is not double buffered. + Any invalid value for <span style="font-style: italic;">buffer</span> +will raise the error GL_INVALID_ENUM.<br> +<br> +The default read source is GL_BACK if the frame buffer is double +buffered. Otherwise, the default read source is GL_FRONT.<br> +<br> +<h2>8.2 Selection Mode</h2> +Selection mode is typically used to implement <span + style="font-style: italic;">picking</span>: determining which +primitive(s) are present at particular window positions. The +command<br> +<br> +<div style="margin-left: 40px;">GLint <span style="font-weight: bold;">glRenderMode</span>(GLenum<span + style="font-style: italic;">mode</span>)<br> +</div> +<br> +is used to enable selection mode. If <span + style="font-style: italic;">mode</span> is GL_SELECTION the graphics +library is put into selection mode. If <span + style="font-style: italic;">mode</span> is GL_RENDER the graphic +library is put into normal rendering mode. Any other value for <span + style="font-style: italic;">mode</span> will raise the error +GL_INVALID_ENUM.<br> +<br> +When in selection mode rendering commands will not effect the +framebuffer. Instead, a record of the primitives that would have +been drawn is placed in the <span style="font-style: italic;">selection</span> <span + style="font-style: italic;">buffer</span>. The selection buffer +is specified with the command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glSelectionBuffer</span>(GLsizei<span + style="font-style: italic;">n</span>, GLuint *<span + style="font-style: italic;">buffer</span>)<br> +</div> +<span style="font-style: italic;"></span><span + style="font-style: italic;"><br> +buffer</span> is an array of <span style="font-style: italic;">n</span> +unsigned integers. No more than <span style="font-style: italic;">n</span> +values will be placed in the buffer.<br> +<br> +The <span style="font-style: italic;">name stack</span> is a stack +(LIFO) of unsigned integer names. The following commands +manipulate the name stack:<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glInitNames</span>(void)<br> +void <span style="font-weight: bold;">glPushName</span>(GLuint <span + style="font-style: italic;">name</span>)<br> +void <span style="font-weight: bold;">glPopName</span>(void)<br> +void <span style="font-weight: bold;">glLoadName</span>(GLuint <span + style="font-style: italic;">name</span>)<br> +</div> +<br> +<span style="font-weight: bold;">glInitNames</span> resets the name +stack to an empty state. <span style="font-weight: bold;">glPushName<span + style="font-style: italic;"> </span></span>pushes the given <span + style="font-style: italic;">name</span> value onto the stack. <span + style="font-weight: bold;">glPopName</span> pops the top name from the +stack. <span style="font-weight: bold;">glLoadName<span + style="font-style: italic;"> </span></span>replaces the top value on +the stack with the specified <span style="font-style: italic;">name</span>. + Stack underflow and overflow conditions cause the errors +GL_STACK_OVERFLOW and GL_STACK_UNDERFLOW to be raised.<br> +<br> +While in selection mode, primitives (points, lines, polygons) are +transformed and clip-tested normally. Primitives which aren't +discarded by clipping cause the <span style="font-style: italic;">hit</span> <span + style="font-style: italic;">data</span> to be updated. The hit +data consists of three pieces of information: a hit flag, a minimum Z +value and a maxium Z value. First, the hit flag is set. + Then, for each of the primitive's vertices, the vertex Z value is +compared to the minimum and maximum Z values. The minimum Z value +is updated if the vertex's Z value is less than the minimum Z value. + The maximum Z value is updated if the vertex's Z value is greater +than the maximum Z value.<br> +<br> +When any of <span style="font-weight: bold;">glInitNames</span><span + style="font-style: italic;"><span style="font-style: italic;">, </span></span><span + style="font-weight: bold;">glPushName</span>, <span + style="font-weight: bold;">glPopName</span>, <span + style="font-weight: bold;">glLoadName</span> or <span + style="font-weight: bold;">glRenderMode</span> are called and the hit +flag is set, a <span style="font-style: italic;">hit record</span> is +written to the selection buffer.<br> +<br> +A hit record consists of a sequence of unsigned integers. The +first value is the size of the name stack. The second value is the +minimum Z value multiplied by 2<sup>32</sup>-1. The third value is +the maximum Z value multiplied by 2<sup>32</sup>-1. The remaining +values are the values in the name stack, in bottom to top order. + The hit flag is cleared after a hit record is written to the +selection buffer. Hit records are places sequentially into the +selection buffer until it is full or selection mode is terminated.<br> +<br> +Selection mode is terminated by calling <span + style="font-weight: bold;">glRenderMode</span>(GL_RENDER). The +return value of <span style="font-weight: bold;">glRenderMode</span> +will be -1 if the selection buffer overflowed. Otherwise, the +return value will indicate the number of values written into the +selection buffer.<br> +<br> +<h2>8.3 Synchronization</h2> +The command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glFlush</span>(void)<br> +</div> +<br> +makes the graphics library to flush all pending graphics commands. + The command<br> +<div style="margin-left: 40px;"><br> +void <span style="font-weight: bold;">glFinish</span>(void)<br> +</div> +<br> +makes the graphics library flush the command queue and wait until those +commands are completed. <span style="font-weight: bold;">glFlush</span> +will not return until all previous graphics commands have been fully +completed.<br> +<br> +These commands are typically used to force completion of rendering to +the front color buffer. Otherwise, rendering to the front color +buffer may not appear. The <span style="font-style: italic;">swapbuffers</span> +command (part of the window system binding library) does an implicit +flush before swapping the front and back color buffers. The <span + style="font-weight: bold;">glReadPixels</span> command also does an +implicit flush before reading pixel data from the frame buffer.<br> +<h1>9. State Queries</h1> +The current value of nearly all library state variables can be queried. + This chapter describes the commands used for querying the value of +state variables.<br> +<br> +<h2>9.1 General State Queries</h2> +The command<br> +<br> +<div style="margin-left: 40px;">void <span style="font-weight: bold;">glGetFloatv</span>(GLenum<span + style="font-style: italic;">pname</span>, GLfloat *<span + style="font-style: italic;">values</span>)<br> +</div> +<br> +returns the value(s) of the state variable specified by <span + style="font-style: italic;">pname</span>. The following table +lists all accepted values for <span style="font-style: italic;">pname</span> +and a description of the value(s). Specifying any other value for <span + style="font-style: italic;">pname</span> causes the error +GL_INVALID_ENUM to be raised.<br> +<br> +<table cellpadding="2" cellspacing="2" border="1" + style="text-align: left; width: 90%; margin-left: auto; margin-right: auto;"> + <tbody> + <tr> + <td style="vertical-align: top;">Variable (<span + style="font-style: italic;">pname)</span><br> + </td> + <td style="vertical-align: top;">Number of values<br> + </td> + <td style="vertical-align: top;">Value(s) Description<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ALPHA_BITS<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Number of bits per alpha value +in the frame buffer.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ALPHA_TEST<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Zero if the alpha test is +disabled.<br> +One if the alpha test is enabled.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ALPHA_TEST_FUNC<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">The alpha test function.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_BLEND<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Zero if blending is disabled.<br> +One if blending is enabled.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_BLEND_DST<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Blend destination function/term.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_BLEND_SRC<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Blend source function/term.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_BLUE_BITS<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Number of bits per blue value in +the frame buffer.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_COLOR_CLEAR_VALUE<br> + </td> + <td style="vertical-align: top;">4<br> + </td> + <td style="vertical-align: top;">Clear color (red, green, blue, +alpha).<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_COLOR_WRITE_MASK<br> + </td> + <td style="vertical-align: top;">4<br> + </td> + <td style="vertical-align: top;">Color buffer writemask (red, +green, blue, alpha).<br> +Zero if writing is disabled.<br> +One if writing is enabled.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_CULL_FACE<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Zero if polygon culling is +disabled.<br> +One if polygon culling is enabled.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_CULL_FACE_MODE<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Polygon cull mode: GL_FRONT, +GL_BACK or GL_FRONT_AND_BACK.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_CURRENT_COLOR<br> + </td> + <td style="vertical-align: top;">4<br> + </td> + <td style="vertical-align: top;">Current color (red, green, blue, +alpha).<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_CURRENT_RASTER_COLOR<br> + </td> + <td style="vertical-align: top;">4<br> + </td> + <td style="vertical-align: top;">Current raster position color +(red, green, blue, alpha).<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_CURRENT_RASTER_TEXTURE_COORDS<br> + </td> + <td style="vertical-align: top;">4<br> + </td> + <td style="vertical-align: top;">Current raster position texture +coordinates (s, t, r, q).<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_CURRENT_RASTER_POSITION<br> + </td> + <td style="vertical-align: top;">4<br> + </td> + <td style="vertical-align: top;">Current raster position (x, y, +z, w).<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_CURRENT_POSITION_VALID<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Zero if current raster position +is invalid.<br> +One if current raster position is valid.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_CURRENT_TEXTURE_COORDS<br> + </td> + <td style="vertical-align: top;">4<br> + </td> + <td style="vertical-align: top;">Current texture coordinates (s, +t, r, q)<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_DOUBLEBUFFER<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Zero if color buffer is +single-buffered.<br> +One if color buffer is double-buffered.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_DRAW_BUFFER<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Current color draw buffer: +GL_FRONT or GL_BACK.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_FRONT_FACE</td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Polygon front-face winding: +GL_CW or GL_CCW.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_GREEN_BITS<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Number of bits per green value +in the frame buffer.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LINE_SMOOTH<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Zero if line smoothing is +disabled.<br> +One if line smoothing is enabled.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LINE_STIPPLE<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Zero if line stippling is +disabled.<br> +One if line stippling is enabled.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LINE_STIPPLE_PATTERN<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Line stipple pattern.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LINE_STIPPLE_REPEAT<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Line stipple repeat factor.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LINE_WIDTH<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Line width in pixels.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LINE_WIDTH_GRANULARITY<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Aliased line width granularity.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LINE_WIDTH_RANGE<br> + </td> + <td style="vertical-align: top;">2<br> + </td> + <td style="vertical-align: top;">Minimum and maximum aliased line +widths.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_ALIASED_LINE_WIDTH_RANGE<br> + </td> + <td style="vertical-align: top;">2<br> + </td> + <td style="vertical-align: top;">Minimum and maximum antialiased +line widths.</td> + </tr> + <tr> + <td style="vertical-align: top;">GL_COLOR_LOGIC_OP<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Zero if logicop is disabled.<br> +One if logicop is enabled.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_LOGIC_OP_MODE<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Logicop function.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_MATRIX_MODE<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Matrix mode: GL_MODELVIEW or +GL_PROJECTION.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_MAX_MODELVIEW_STACK_DEPTH<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Maximum size of the modelview +matrix stack.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_MAX_NAME_STACK_DEPTH<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Maximum size of the selection +name stack.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_MAX_PROJECTION_STACK_DEPTH<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Maximum size of the projection +matrix stack.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_MAX_TEXTURE_SIZE<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Maximum 2D texture image width +and height.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_MAX_VIEWPORT_DIMS<br> + </td> + <td style="vertical-align: top;">2</td> + <td style="vertical-align: top;">Maximum viewport width and +height in pixels.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_MODELVIEW_MATRIX<br> + </td> + <td style="vertical-align: top;">16<br> + </td> + <td style="vertical-align: top;">Current/top modelview matrix +values.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_MODELVIEW_MATRIX_STACK_DEPTH<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Current size of the modelview +matrix stack.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_NAME_STACK_DEPTH<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Current size of the selection +name stack.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_PACK_ROW_LENGTH<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Pixel packing row length.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_PACK_SKIP_PIXELS<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Pixel packing skip pixels.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_PACK_SKIP_ROWS<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Pixel packing skip rows.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_POLYGON_MODE<br> + </td> + <td style="vertical-align: top;">2<br> + </td> + <td style="vertical-align: top;">Current front and back polygon +modes: GL_POINT, GL_LINE or GL_FILL.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_POLYGON_SMOOTH<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Zero if polygon smoothing is +disabled.<br> +One if polygon smoothing is enabled.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_PROJECTION_MATRIX<br> + </td> + <td style="vertical-align: top;">16<br> + </td> + <td style="vertical-align: top;">Current/top projection matrix +values.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_PROJECTION_STACK_DEPTH<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Current size of projection +matrix stack.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_READ_BUFFER<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Current read buffer: GL_FRONT or +GL_BACK.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_RED_BITS<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Number of bits per red value in +the frame buffer.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_RENDER_MODE<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Current rendering mode: +GL_RENDER or GL_SELECTION.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_RGBA_MODE<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Always one.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_SCISSOR_BOX<br> + </td> + <td style="vertical-align: top;">4<br> + </td> + <td style="vertical-align: top;">Scissor box (x, y, width, +height).<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_SCISSOR_TEST<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Zero if scissor test is disabled.<br> +One if scissor test is enabled.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_SELECTION_BUFFER_SIZE<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Size of selection buffer.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_SHADE_MODEL<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Shade model: GL_FLAT or +GL_SMOOTH.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_STENCIL_BITS<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Number of bits per stencil value +in the frame buffer.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_STENCIL_CLEAR_VALUE<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Stencil buffer clear value.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_STENCIL_FAIL<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Stencil fail operation.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_STENCIL_FUNC<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Stencil function.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_STENCIL_REF<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Stencil reference value.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_STENCIL_TEST<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Zero if stencil test is disabled.<br> +One if stencil test is enabled.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_STENCIL_VALUE_MASK<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Stencil mask value.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_STENCIL_WRITE_MASK<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Stencil buffer write mask.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_TEXTURE_2D<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Zero if 2D texture mapping is +disabled.<br> +One if 2D texture mapping is enabled.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_TEXTURE_BINDING_2D</td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Name of currently bound 2D +texture object.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_TEXTURE_ENV_COLOR<br> + </td> + <td style="vertical-align: top;">4<br> + </td> + <td style="vertical-align: top;">Texture environment color (red, +green, blue, alpha).<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_TEXTURE_ENV_MODE<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Texture environment mode.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_UNPACK_ROW_LENGTH<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Pixel unpacking row length.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_UNPACK_LSB_FIRST<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Zero if most significant bit is +unpacked first for bitmaps.<br> +One if least significant bit is unpacked first for bitmaps.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_UNPACK_SKIP_PIXELS<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Pixel unpacking skip pixels.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_UNPACK_SKIP_ROWS<br> + </td> + <td style="vertical-align: top;">1<br> + </td> + <td style="vertical-align: top;">Pixel unpacking skip rows.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_VIEWPORT<br> + </td> + <td style="vertical-align: top;">4<br> + </td> + <td style="vertical-align: top;">Current viewport (x, y, width, +height).<br> + </td> + </tr> + </tbody> +</table> +<br> +<br> +<h2>9.2 String Queries</h2> +The command<br> +<br> +<div style="margin-left: 40px;">const GLubyte *<span + style="font-weight: bold;">glGetString</span>(GLenum <span + style="font-style: italic;">name</span>)<br> +</div> +<br> +is used to query string-valued values. The legal values for <span + style="font-style: italic;">name</span> are described in the following +table:<br> +<br> +<table cellpadding="2" cellspacing="2" border="1" + style="text-align: left; width: 80%; margin-left: auto; margin-right: auto;"> + <tbody> + <tr> + <td style="vertical-align: top;"><span style="font-style: italic;">name</span><br> + </td> + <td style="vertical-align: top;">Return value<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_VERSION<br> + </td> + <td style="vertical-align: top;">The library version, such as +"1.2".<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_RENDERER<br> + </td> + <td style="vertical-align: top;">The renderer, such as "Mesa DRI +Radeon". XXX final?<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_VENDER<br> + </td> + <td style="vertical-align: top;">The vender of this +implementation, such as "Tungsten Graphics, Inc."<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_EXTENSIONS<br> + </td> + <td style="vertical-align: top;">A white-space separated list of +the supported OpenGL extensions.<br> + </td> + </tr> + </tbody> +</table> +<br> +<br> +<h2>9.3 Error Queries</h2> +The command<br> +<br> +<div style="margin-left: 40px;">GLenum <span style="font-weight: bold;">glGetError</span>(void)<br> +</div> +<br> +returns the current error code. The current error code will be +set by a GL command when an error condition has been detected. If +the current error code is already set, subsequent errors will not be +recorded. The error code is reset/cleared to GL_NO_ERROR when <span + style="font-weight: bold;">glGetError</span> returns. The +following error codes are possible:<br> +<br> +<table cellpadding="2" cellspacing="2" border="1" + style="text-align: left; width: 80%; margin-left: auto; margin-right: auto;"> + <tbody> + <tr> + <td style="vertical-align: top;">Error code<br> + </td> + <td style="vertical-align: top;">Meaning<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_NO_ERROR<br> + </td> + <td style="vertical-align: top;">No error has been recorded.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_INVALID_ENUM<br> + </td> + <td style="vertical-align: top;">An enum parameter had an invalid +value.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_INVALID_VALUE<br> + </td> + <td style="vertical-align: top;">A numeric parameter had an +invalid value.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_INVALID_OPERATION<br> + </td> + <td style="vertical-align: top;">A function was called when not +legal to do so.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_STACK_OVERFLOW<br> + </td> + <td style="vertical-align: top;">The current transformation +matrix stack is full.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_STACK_UNDERFLOW<br> + </td> + <td style="vertical-align: top;">The current transformation +matrix stack is empty.<br> + </td> + </tr> + <tr> + <td style="vertical-align: top;">GL_OUT_OF_MEMORY<br> + </td> + <td style="vertical-align: top;">The system ran out of dynamic +memory.<br> + </td> + </tr> + </tbody> +</table> +<br> +<br> +<h1>10. Unsupported Features</h1> +This section lists other features and functions which are not supported +and not previously discussed.<br> +<br> +<h2>10.1 Feedback Mode</h2> +Feedback mode and the following related functions are not supported.<br> +<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glFeedbackBuffer</span><br> +<span style="font-weight: bold;">glPassThrough</span><br> +</div> +<br> +<h2>10.2 1D and 3D Textures<br> +</h2> +Only 2D texture images are supported. The following functions +used to specify 1D and 3D texture images are not supported:<br> +<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glTexImage1D</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glTexImage3D</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glTexSubImage1D</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;"> glTexSubImage3D</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glCopyTexImage1D</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;"> glCopyTexSubImage1D</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;"> glCopyTexSubImage3D</span><br> +</div> +<br> +<h2>10.3 Alternate Texture Image Commands<br> +</h2> +Texture images may only be specified with <span + style="font-weight: bold;">glTexImage2D</span>. The following +alternate texture image commands are not supported:<br> +<br> +<div style="margin-left: 40px; font-weight: bold;">glTexSubImage2D<br> +glCopyTexImage2D<br> +glCopyTexSubImage2D<br> +</div> +<br> +<h2>10.4 Proxy Textures</h2> +Proxy textures are not supported and the GL_PROXY_TEXTURE_2D token is +not supported by any function.<br> +<br> +<h2>10.5 Copy and Draw Pixels<br> +</h2> +The following commands are not supported:<br> +<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glDrawPixels<br> +glCopyPixels<br> +glPixelZoom<br> +<br> +</span></div> +<h2>10.6 Color Index Mode<br> +</h2> +Color index mode and the following related commands are not supported:<br> +<br> +<span style="font-weight: bold;"></span> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glIndexub<br> +</span><span style="font-weight: bold;">glIndexi</span><br> +<span style="font-weight: bold;">glIndexs<br> +glIndexf<br> +glIndexd<br> +</span><span style="font-weight: bold;">glIndexubv<br> +</span><span style="font-weight: bold;">glIndexiv</span><br> +<span style="font-weight: bold;">glIndexsv<br> +glIndexfv<br> +glIndexdv</span><span style="font-weight: bold;"><br> +glIndexMask<br> +</span><span style="font-weight: bold;">glClearIndex<br> +glIndexPointer</span><br style="font-weight: bold;"> +<br> +</div> +<h2>10.7 Pixel Transfer Operations</h2> +The pixel transfer operations (scale, bias, look-up table, etc) are not +supported and the following commands are omitted:<br> +<br style="font-weight: bold;"> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glPixelTransferf</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glPixelTransferi</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glPixelMapfv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glPixelMapuiv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glPixelMapusv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glGetPixelMapfv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glGetPixelMapuiv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glGetPixelMapusv</span><br> +</div> +<br> +<h2>10.8 Hints</h2> +Hints and the following related command is not supported:<br> +<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glHint<br> +</span><br> +</div> +<h2>10.9 State Query Commands<br> +</h2> +The following state query commands are not supported:<br> +<br> +<div style="margin-left: 40px; font-weight: bold;">glGetBooleanv<br> +glGetIntegerv<br> +glGetDoublev<br> +glGetPointerv<br> +glGetTexEnvi<br> +glGetTexEnvf<br> +glGetTexParameteriv<br> +glGetTexParameterfv<br> +glGetTexLevelParameteriv<br> +glGetTexLevelParameterfv<br> +glGetTexImage<br> +glGetClipPlane<br> +</div> +<br> +<h2>10.10 Attribute Stacks</h2> +State attribute stacks and the following related commands are not +supported:<br> +<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glPushAttrib</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glPopAtttrib</span><br> +<br style="font-weight: bold;"> +</div> +<h2>10.11 Double-Valued Functions</h2> +All functions which take double-precision floating point values, but +for which there is an equivalent single-precision valued function, are +omitted. This includes, but is not limited to:<br> +<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glVertex2d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glVertex2dv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glVertex3d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;"> glVertex3dv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glVertex4d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;"> glVertex4dv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glColor3d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glColor3d</span><span + style="font-weight: bold;">v</span><br style="font-weight: bold;"> +<span style="font-weight: bold;">glColor4d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;"> glColor4dv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glTexCoord1d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glTexCoord1d</span><span + style="font-weight: bold;">v</span><br style="font-weight: bold;"> +<span style="font-weight: bold;">glTexCoord2d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;"> glTexCoord2dv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glTexCoord3d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;"> glTexCoord3dv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glTexCoord4d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;"> glTexCoord4dv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glRasterPos2d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;"> glRasterPos2dv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glRasterPos3d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;"> glRasterPos3dv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glRasterPos4d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;"> glRasterPos4dv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glLoadMatrixd</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glMultMatrixd</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glScaled</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glRotated</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glTranslated<br> +glRectd<br> +glRectdv<br> +</span> <span style="font-weight: bold;"><br> +</span> </div> +<h2>10.12 Evaluators</h2> +Evaluators and the following related commands are not supported:<br> +<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glMap1f</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glMap2d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glMap2f</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glGetMapdv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glGetMapfv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glGetMapiv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glEvalCoord1d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glEvalCoord1f</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glEvalCoord1dv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glEvalCoord1fv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glEvalCoord2d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glEvalCoord2f</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glEvalCoord2dv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glEvalCoord2fv</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glMapGrid1d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glMapGrid1f</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glMapGrid2d</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glMapGrid2f</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glEvalPoint1</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glEvalPoint2</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glEvalMesh1</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glEvalMesh2</span><br + style="font-weight: bold;"> +</div> +<br> +<h2>10.13 Display Lists</h2> +Display lists and the following related commands are not supported:<br> +<br> +<div style="margin-left: 40px; font-weight: bold;">glIsList<br> +glDeleteLists<br> +glGenLists<br> +glNewList<br> +glEndList<br> +glCallList<br> +glCallLists<br> +glListBase<br> +</div> +<br> +<h2>10.14 Accumulation Buffer</h2> +The accumulation buffer and the following related commands are not +supported:<br> +<br style="font-weight: bold;"> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glAccum</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glClearAccum</span><br> +</div> +<br> +<h2>10.15 Fog</h2> +Fog and the following related commands are not supported:<br> +<br> +<div style="margin-left: 40px; font-weight: bold;"> glFogi<br> +glFogf<br> +glFogiv<br> +glFogfv<br> +</div> +<br> +<h2>10.16 Depth Test</h2> +Depth testing and the following related commands are not supported:<br> +<br> +<div style="margin-left: 40px;"><span style="font-weight: bold;">glDepthFunc</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glDepthMask</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glDepthRange</span><br + style="font-weight: bold;"> +<span style="font-weight: bold;">glClearDepth</span><br> +</div> +<br> +<h2>10.17 Imaging Subset</h2> +The OpenGL imaging subset (which implements features such as +convolution, histogram, min/max recording, color matrix and color +tables) is not supported.<br> +<br> +<br> +<h1>Appendix A: Issues</h1> +This appendix lists documentation and subset issues with their current +status.<br> +<br> +<h2>A.1 Vertex Arrays</h2> +Should vertex arrays be supported? Is there a performance +advantage?<br> +<br> +RESOLUTION: No, there isn't enough of a performance advantage to +justify them.<br> +<br> +<h2>A.2 Polygon Antialiasing and Edge Flags</h2> +Should edge flags be supported for antialiasing?<br> +<br> +Edge flags don't effect antialiasing, at least not normally. A +number of approaches to antialiasing have been summarized in email.<br> +<br> +RESOLUTION: open<br> +<br> +<h2>A.3 glRasterPos vs. glWindowPos</h2> +Should glRasterPos and/or glWindowPos commands be supported?<br> +<br> +RESOLUTION: Closed: implement glRasterPos commands, but not glWindowPos +commands.<br> +<br> +<h2>A.4 GL_IBM_rasterpos_clip extension</h2> +Should the GL_IBM_rasterpos_clip extension be implemented?<br> +<br> +RESOLUTION: No. It's not required.<br> +<br> +<h2>A.5 Image Formats and Types</h2> +Which image formats and types should be supported for <span + style="font-weight: bold;">glTexImage2D</span> and <span + style="font-weight: bold;">glReadPixels</span>?<br> +<br> +OpenGL supports a <span style="font-weight: bold;">large</span> variety +of image formats and data types. Only a few are commonly used. + We propose a subset.<br> +<br> +For <span style="font-weight: bold;">glTexImage2D</span> only allow <span + style="font-style: italic;">type</span>=GL_UNSIGNED_BYTE and <span + style="font-style: italic;">format</span>=GL_RGBA, GL_RGB, +GL_INTENSITY. Only allow <span style="font-style: italic;">internalFormat</span> +to be GL_RGBA, GL_RGB or GL_INTENSITY as well. Basically, only +support image formats/types that are directly supported by the Radeon +hardware. This will allow <span style="font-weight: bold;">glTexImage2D</span> +to basically just use <span style="font-weight: bold;">memcpy</span> to +copy texture images.<br> +<br> +For <span style="font-weight: bold;">glReadPixels</span>, only allow <span + style="font-style: italic;">type</span> = GL_UNSIGNED_BYTE or GL_FLOAT. + Only allow <span style="font-style: italic;">format</span> = +GL_RGB or GL_RGBA. This is just enough to support the OpenGL +conformance tests.<br> +<br> +RESOLUTION: open<br> +<br> +<h2>A.6 Texture Environment Modes</h2> +Which texure environment modes should be supported? OpenGL 1.2 +has GL_REPLACE, GL_MODULATE, GL_DECAL and GL_BLEND. GL_DECAL isn't +defined for all base internal texture formats. GL_ADD is another +useful mode. Perhaps drop GL_DECAL mode and add GL_ADDmode.<br> +<br> +RESOLUTION: open<br> +<br> +<h2>A.7 Truncated Mipmaps and LOD Control</h2> +Should we support the GL_TEXTURE_BASE_LEVEL, GL_TEXTURE_MAX_LEVEL, +GL_TEXTURE_MIN_LOD and GL_TEXTURE_MAX_LOD texture parameters?<br> +<br> +RECOMENDATION: We propose omitting these features at this time, +in the interest of simplifiying the driver.<br> +<br> +RESOLUTION: open<br> +<br> +<h2>A.8 Texture Priorities and Residency</h2> +Should the subset support texture prorities via <span + style="font-weight: bold;">glPrioritizeTextures</span> and the <span + style="font-weight: bold;">glAreTexturesResident</span> command?<br> +<br> +RECOMENDATION: Few applications use these features and functions. + We propose omitting them to simplify the driver.<br> +<br> +RESOLUTION: open<br> +<br> +<h2>A.9 Pixel Pack/Unpack Alignment Control</h2> +Should we support the GL_PACK_ALIGNMENT and GL_UNPACK_ALIGNMENT options?<br> +<br> +These are used to align pixel data addresses to 1, 2 and 4-byte +multiples for <span style="font-weight: bold;">glBitmap, glTexImage2D</span> +and <span style="font-weight: bold;">glReadPixels</span>. These +aren't strictly needed since the user can provide a 1, 2 or 4-byte +aligned address and appropriate GL_PACK_ROW_LENGTH or +GL_UNPACK_ROW_LENGTH values instead.<br> +<br> +RECOMENDATION: We recommend omitting them to simplify the driver.<br> +<br> +RESOLUTION: open<br> +<br> +<h2>A.10 Pixel Pack/Unpack Skip Rows/Pixels Control</h2> +Should we support the GL_UNPACK_SKIP_PIXELS, GL_UNPACK_SKIP_ROWS, +GL_PACK_SKIP_PIXELS and GL_PACK_SKIP_ROWS options for pixel +unpacking/packing?<br> +<br> +These options aren't really needed since the user can adjust the start +address and GL_PACK/UNPACK_ROW_LENGTH parameters to achive the same +effect.<br> +<br> +RECOMENDATION: They're currently included in this document, but +we recommend omitting them.<br> +<br> +RESOLUTION: open<br> +<br> +<h2>A.11 Texture State Queries</h2> +Should we support the command <span style="font-weight: bold;">glGetTexEnvi/fv, +glGetTexParameteri/fv</span> and <span style="font-weight: bold;">glGetTexLevelParameteri/fv</span>?<br> +<br> +RECOMENDATION: No. They're seldom needed and their +implementation is several hundred lines of code in length.<br> +<br> +RESOLUTION: open<br> +<br> +<h2>A.12 glGetIntegerv, glGetBooleanv and glGetDoublev</h2> +Should we support the commands <span style="font-weight: bold;">glGetIntegerv, +glGetBooleanv </span>and <span style="font-weight: bold;">glGetDoublev</span> +in addition to <span style="font-weight: bold;">glGetFloatv</span>?<br> +<br> +RECOMENDATION: Omit the boolean, integer and double-valued +functions. All state values which can be queried by these commands can +be expressed as floating point values and queried with <span + style="font-weight: bold;">glGetFloatv</span>. The +implementation of the other three commands involves many lines of code.<br> +<br> +RESOLUTION: open<br> +<h2>A.13 glBitmap and Per-Fragment Operations</h2> +Should bitmaps rendered with <span style="font-weight: bold;">glBitmap</span> +be subjected to the per-fragment operations?<br> +<br> +If bitmaps are implemented with points it will be easy to implement the +per-fragment operations. Otherwise, it could be difficult.<br> +<br> +RESOLUTION: Open:<br> +<br> +<p> </p> +</body> +</html> |