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/**
* Draw stencil region
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <GL/glew.h>
#include "glut_wrap.h"
static int Win;
static int WinWidth = 600, WinHeight = 200;
static GLfloat Xrot = 0.0, Yrot = 0.0;
#define WIDTH 256
#define HEIGHT 150
static GLubyte Image[HEIGHT][WIDTH];
static void
DrawStencilPixels(GLint x, GLint y, GLsizei w, GLsizei h,
const GLubyte *stencil)
{
/* This program is run eight times, once for each stencil bit.
* The stencil values to draw are found in an 8-bit alpha texture.
* We read the texture/stencil value and test if bit 'b' is set.
* If the bit is set, result.A will be non-zero. Finally, use
* alpha test and stencil test to update the stencil buffer.
*
* The basic algorithm for checking if a bit is set is:
* if (is_odd(value / (1 << bit)))
* result is one (or non-zero).
* else
* result is zero.
* The program parameter contains two values:
* parm.x = 255 / (1 << bit)
* parm.y = 0.5
*/
static const char *program =
"!!ARBfp1.0\n"
"PARAM parm = program.local[0]; \n"
"TEMP t; \n"
"TEX t, fragment.texcoord[0], texture[0], RECT; \n"
"# t = t * 255 / bit \n"
"MUL t.x, t.a, parm.x; \n"
"# t = (int) t \n"
"FRC t.y, t.x; \n"
"SUB t.x, t.x, t.y; \n"
"# t = 5 * 0.5 \n"
"MUL t.x, t.x, parm.y; \n"
"# alpha = frac(t) \n"
"FRC result.color, t.x; \n"
"END \n";
GLuint prog;
GLint bit;
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glTexImage2D(GL_TEXTURE_RECTANGLE_ARB, 0, GL_ALPHA, w, h, 0,
GL_ALPHA, GL_UNSIGNED_BYTE, stencil);
glTexParameteri(GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glGenProgramsARB(1, &prog);
glBindProgramARB(GL_FRAGMENT_PROGRAM_ARB, prog);
glProgramStringARB(GL_FRAGMENT_PROGRAM_ARB, GL_PROGRAM_FORMAT_ASCII_ARB,
strlen(program), (const GLubyte *) program);
glEnable(GL_FRAGMENT_PROGRAM_ARB);
glPushMatrix();
glTranslatef(x, y, 0);
glEnable(GL_ALPHA_TEST);
glAlphaFunc(GL_GREATER, 0.0);
glEnable(GL_STENCIL_TEST);
glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
for (bit = 0; bit < 8; bit++) {
GLuint mask = 1 << bit;
glStencilFunc(GL_ALWAYS, 255/*mask*/, mask);
glStencilMask(mask);
glProgramLocalParameter4fARB(GL_FRAGMENT_PROGRAM_ARB, 0,
// 1.0 / bit, 0.5, 0.0, 0.0);
255.0 / mask, 0.5, 0.0, 0.0);
glBegin(GL_TRIANGLE_FAN);
glTexCoord2f(0, 0); glVertex2f(0, 0);
glTexCoord2f(w, 0); glVertex2f(w, 0);
glTexCoord2f(w, h); glVertex2f(w, h);
glTexCoord2f(0, h); glVertex2f(0, h);
glEnd();
}
glPopMatrix();
glDisable(GL_FRAGMENT_PROGRAM_ARB);
glDisable(GL_ALPHA_TEST);
glDisable(GL_STENCIL_TEST);
}
static void
Draw(void)
{
GLint x0 = 5, y0= 5, x1 = 10 + WIDTH, y1 = 5;
GLubyte tmp[HEIGHT][WIDTH];
GLint max, i, j;
glClearColor(0.2, 0.2, 0.8, 0.0);
glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
if (0) {
DrawStencilPixels(x0, y0, WIDTH, HEIGHT, (GLubyte*) Image);
} else {
glWindowPos2i(x0, y0);
glDrawPixels(WIDTH, HEIGHT, GL_STENCIL_INDEX,
GL_UNSIGNED_BYTE, (GLubyte*) Image);
}
glReadPixels(x0, y0, WIDTH, HEIGHT, GL_STENCIL_INDEX, GL_UNSIGNED_BYTE, tmp);
max = 0;
for (i = 0; i < HEIGHT; i++) {
for (j = 0; j < WIDTH; j++) {
if (tmp[i][j] > max)
max = tmp[i][j];
}
}
printf("max = %d\n", max);
glWindowPos2i(x1, y1);
glDrawPixels(WIDTH, HEIGHT, GL_LUMINANCE, GL_UNSIGNED_BYTE, tmp);
glutSwapBuffers();
}
static void
Reshape(int width, int height)
{
WinWidth = width;
WinHeight = height;
glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, width, 0, height, -1, 1);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
static void
Key(unsigned char key, int x, int y)
{
(void) x;
(void) y;
switch (key) {
case 27:
glutDestroyWindow(Win);
exit(0);
break;
}
glutPostRedisplay();
}
static void
SpecialKey(int key, int x, int y)
{
const GLfloat step = 3.0;
(void) x;
(void) y;
switch (key) {
case GLUT_KEY_UP:
Xrot -= step;
break;
case GLUT_KEY_DOWN:
Xrot += step;
break;
case GLUT_KEY_LEFT:
Yrot -= step;
break;
case GLUT_KEY_RIGHT:
Yrot += step;
break;
}
glutPostRedisplay();
}
static void
Init(void)
{
int i, j;
for (i = 0; i < HEIGHT; i++) {
for (j = 0; j < WIDTH; j++) {
Image[i][j] = j;
}
}
}
int
main(int argc, char *argv[])
{
glutInit(&argc, argv);
glutInitWindowSize(WinWidth, WinHeight);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_STENCIL);
Win = glutCreateWindow(argv[0]);
glewInit();
glutReshapeFunc(Reshape);
glutKeyboardFunc(Key);
glutSpecialFunc(SpecialKey);
glutDisplayFunc(Draw);
Init();
glutMainLoop();
return 0;
}
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