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/*
* Test the GL_PERSPECTIVE_CORRECTION_HINT setting and its effect on
* color interpolation.
*
* Press 'i' to toggle between GL_NICEST/GL_FASTEST/GL_DONT_CARE.
*
* Depending on the driver, the hint may make a difference, or not.
*/
#include <stdlib.h>
#include <stdio.h>
#include <GL/glut.h>
static GLenum PerspHint = GL_DONT_CARE;
static void
init(void)
{
GLubyte image[256][256][4];
GLuint i, j;
for (i = 0; i < 256; i++) {
for (j = 0; j < 256; j++) {
image[i][j][0] = j;
image[i][j][1] = j;
image[i][j][2] = j;
image[i][j][3] = 255;
}
}
glTexImage2D(GL_TEXTURE_2D, 0, 4, 256, 256, 0,
GL_RGBA, GL_UNSIGNED_BYTE, image);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
printf("GL_RENDERER = %s\n", (char *) glGetString(GL_RENDERER));
}
static void
display(void)
{
switch (PerspHint) {
case GL_NICEST:
printf("hint = GL_NICEST\n");
break;
case GL_FASTEST:
printf("hint = GL_FASTEST\n");
break;
case GL_DONT_CARE:
printf("hint = GL_DONT_CARE\n");
break;
default:
;
}
glClear(GL_COLOR_BUFFER_BIT);
#if 1
glBegin(GL_QUADS);
/* exercise perspective interpolation */
glColor3f(0.0, 0.0, 0.0); glVertex3f(-1.0, -1.0, -1.0);
glColor3f(0.0, 0.0, 0.0); glVertex3f(-1.0, 1.0, -1.0);
glColor3f(0.0, 1.0, 0.0); glVertex3f( 7.0, 1.0, -7.0);
glColor3f(0.0, 1.0, 0.0); glVertex3f( 7.0, -1.0, -7.0);
/* stripe of linear interpolation */
glColor3f(0.0, 0.0, 0.0); glVertex3f(-1.0, -0.1, -1.001);
glColor3f(0.0, 0.0, 0.0); glVertex3f(-1.0, 0.1, -1.001);
glColor3f(0.0, 1.0, 0.0); glVertex3f( 1.0, 0.1, -1.001);
glColor3f(0.0, 1.0, 0.0); glVertex3f( 1.0, -0.1, -1.001);
glEnd();
#else
glEnable(GL_TEXTURE_2D);
glBegin(GL_QUADS);
glTexCoord2f(0.0, 0.0); glVertex3f(-1.0, 0.0, -1.0);
glTexCoord2f(0.0, 1.0); glVertex3f(-1.0, 1.0, -1.0);
glTexCoord2f(1.0, 1.0); glVertex3f( 5.0, 1.0, -7.0);
glTexCoord2f(1.0, 0.0); glVertex3f( 5.0, 0.0, -7.0);
glTexCoord2f(0.0, 0.0); glVertex3f(-1.0, -1.0, -1.001);
glTexCoord2f(0.0, 1.0); glVertex3f(-1.0, 0.0, -1.001);
glTexCoord2f(1.0, 1.0); glVertex3f( 1.0, 0.0, -1.001);
glTexCoord2f(1.0, 0.0); glVertex3f( 1.0, -1.0, -1.001);
glEnd();
#endif
glFlush();
}
static void
reshape(int w, int h)
{
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(90.0, (GLfloat) w / h, 1.0, 300.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
static void
key(unsigned char k, int x, int y)
{
switch (k) {
case 27: /* Escape */
exit(0);
break;
case 'i':
if (PerspHint == GL_FASTEST)
PerspHint = GL_NICEST;
else if (PerspHint == GL_NICEST)
PerspHint = GL_DONT_CARE;
else
PerspHint = GL_FASTEST;
glHint(GL_PERSPECTIVE_CORRECTION_HINT, PerspHint);
break;
default:
return;
}
glutPostRedisplay();
}
int
main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize (500, 500);
glutCreateWindow (argv[0]);
glutReshapeFunc (reshape);
glutDisplayFunc(display);
glutKeyboardFunc(key);
printf("Main quad: perspective projection\n");
printf("Middle stripe: linear interpolation\n");
printf("Press 'i' to toggle interpolation hint\n");
init();
glutMainLoop();
return 0;
}
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