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.. _rasterizer:
Rasterizer
==========
The rasterizer state controls the rendering of points, lines and triangles.
Attributes include polygon culling state, line width, line stipple,
multisample state, scissoring and flat/smooth shading.
Members
-------
flatshade
If set, the provoking vertex of each polygon is used to determine the
color of the entire polygon. If not set, fragment colors will be
interpolated between the vertex colors.
Note that this is separate from the fragment shader input attributes
CONSTANT, LINEAR and PERSPECTIVE. We need the flatshade state at
clipping time to determine how to set the color of new vertices.
Also note that the draw module can implement flat shading by copying
the provoking vertex color to all the other vertices in the primitive.
flatshade_first
Whether the first vertex should be the provoking vertex, for most
primitives. If not set, the last vertex is the provoking vertex.
light_twoside
If set, there are per-vertex back-facing colors. The draw module
uses this state along with the front/back information to set the
final vertex colors prior to rasterization.
front_winding
Indicates the window order of front-facing polygons, either
PIPE_WINDING_CW or PIPE_WINDING_CCW
cull_mode
Indicates which polygons to cull, either PIPE_WINDING_NONE (cull no
polygons), PIPE_WINDING_CW (cull clockwise-winding polygons),
PIPE_WINDING_CCW (cull counter clockwise-winding polygons), or
PIPE_WINDING_BOTH (cull all polygons).
fill_cw
Indicates how to fill clockwise polygons, either PIPE_POLYGON_MODE_FILL,
PIPE_POLYGON_MODE_LINE or PIPE_POLYGON_MODE_POINT.
fill_ccw
Indicates how to fill counter clockwise polygons, either
PIPE_POLYGON_MODE_FILL, PIPE_POLYGON_MODE_LINE or PIPE_POLYGON_MODE_POINT.
poly_stipple_enable
Whether polygon stippling is enabled.
poly_smooth
Controls OpenGL-style polygon smoothing/antialiasing
offset_cw
If set, clockwise polygons will have polygon offset factors applied
offset_ccw
If set, counter clockwise polygons will have polygon offset factors applied
offset_units
Specifies the polygon offset bias
offset_scale
Specifies the polygon offset scale
line_width
The width of lines.
line_smooth
Whether lines should be smoothed. Line smoothing is simply anti-aliasing.
line_stipple_enable
Whether line stippling is enabled.
line_stipple_pattern
16-bit bitfield of on/off flags, used to pattern the line stipple.
line_stipple_factor
When drawinga stippled line, each bit in the stipple pattern is
repeated N times, where N = line_stipple_factor + 1.
line_last_pixel
Controls whether the last pixel in a line is drawn or not. OpenGL
omits the last pixel to avoid double-drawing pixels at the ends of lines
when drawing connected lines.
point_smooth
Whether points should be smoothed. Point smoothing turns rectangular
points into circles or ovals.
point_size_per_vertex
Whether vertices have a point size element.
point_size
The size of points, if not specified per-vertex.
sprite_coord_enable
Specifies if a coord has its texture coordinates replaced or not. This
is a packed bitfield containing the enable for all coords - if all are 0
point sprites are effectively disabled, though points may still be
rendered slightly different according to point_quad_rasterization.
If any coord is non-zero, point_smooth should be disabled, and
point_quad_rasterization enabled.
If enabled, the four vertices of the resulting quad will be assigned
texture coordinates, according to sprite_coord_mode.
sprite_coord_mode
Specifies how the value for each shader output should be computed when
drawing sprites, for each coord which has sprite_coord_enable set.
For PIPE_SPRITE_COORD_LOWER_LEFT, the lower left vertex will have
coordinate (0,0,0,1).
For PIPE_SPRITE_COORD_UPPER_LEFT, the upper-left vertex will have
coordinate (0,0,0,1).
This state is needed by the 'draw' module because that's where each
point vertex is converted into four quad vertices. There's no other
place to emit the new vertex texture coordinates which are required for
sprite rendering.
Note that when geometry shaders are available, this state could be
removed. A special geometry shader defined by the state tracker could
convert the incoming points into quads with the proper texture coords.
point_quad_rasterization
This determines if points should be rasterized as quads or points.
d3d always uses quad rasterization for points, regardless if point sprites
are enabled or not, but OGL has different rules. If point_quad_rasterization
is set, point_smooth should be disabled, and points will be rendered as
squares even if multisample is enabled.
sprite_coord_enable should be zero if point_quad_rasterization is not
enabled.
scissor
Whether the scissor test is enabled.
multisample
Whether :ref:`MSAA` is enabled.
bypass_vs_clip_and_viewport
Whether the entire TCL pipeline should be bypassed. This implies that
vertices are pre-transformed for the viewport, and will not be run
through the vertex shader. Note that implementations may still clip away
vertices that are not in the viewport.
gl_rasterization_rules
Whether the rasterizer should use (0.5, 0.5) pixel centers. When not set,
the rasterizer will use (0, 0) for pixel centers.
Notes
-----
flatshade
^^^^^^^^^
The actual interpolated shading algorithm is obviously
implementation-dependent, but will usually be Gourard for most hardware.
bypass_vs_clip_and_viewport
^^^^^^^^^^^^^^^^^^^^^^^^^^^
When set, this implies that vertices are pre-transformed for the viewport, and
will not be run through the vertex shader. Note that implementations may still
clip away vertices that are not visible.
flatshade_first
^^^^^^^^^^^^^^^
There are several important exceptions to the specification of this rule.
* ``PIPE_PRIMITIVE_POLYGON``: The provoking vertex is always the first
vertex. If the caller wishes to change the provoking vertex, they merely
need to rotate the vertices themselves.
* ``PIPE_PRIMITIVE_QUAD``, ``PIPE_PRIMITIVE_QUAD_STRIP``: This option has no
effect; the provoking vertex is always the last vertex.
* ``PIPE_PRIMITIVE_TRIANGLE_FAN``: When set, the provoking vertex is the
second vertex, not the first. This permits each segment of the fan to have
a different color.
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