opengl入门系列- 颜色混合

#include <GL/glut.h>
#include <stdlib.h>


void init(void)
{
   glClearColor(1.0, 1.0, 0.0, 0.0);

   glBlendFunc(GL_ONE, GL_ONE);
   glEnable(GL_BLEND);
}

void display(void)
{
   glClear(GL_COLOR_BUFFER_BIT);

   glColor3f(0.0, 0.0, 1.0);
 
   glRectf(-0.5,-0.5,0.5,0.5);

   glFlush();
}

void reshape(int w, int h)
{
   GLdouble aspect = (GLdouble) w / h;

   glViewport(0, 0, (GLsizei) w, (GLsizei) h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   if (aspect < 1.0) {
     aspect = 1.0 / aspect;
     glOrtho(-aspect, aspect, -1.0, 1.0, -1.0, 1.0);
   } else
     glOrtho(-1.0, 1.0, -aspect, aspect, -1.0, 1.0);
   glMatrixMode(GL_MODELVIEW);
}

void keyboard(unsigned char key, int x, int y)
{
   switch (key) {
      case 'a': case 'A':
     /* Colors are added as: (1, 1, 0) + (0, 0, 1) = (1, 1, 1)
      *  which will produce a white square on a yellow background.
      */
     glBlendEquation(GL_FUNC_ADD);
     break;

      case 's': case 'S':
     /* Colors are subtracted as: (0, 0, 1) - (1, 1, 0) = (-1, -1, 1)
      *  which is clamped to (0, 0, 1), producing a blue square on a
      *  yellow background
      */     glBlendEquation(GL_FUNC_SUBTRACT);
     break;

      case 'r': case 'R':
     /* Colors are subtracted as: (1, 1, 0) - (0, 0, 1) = (1, 1, -1)
      *  which is clamed to (1, 1, 0).  This produces yellow for both
      *  the square and the background.
      */
     glBlendEquation(GL_FUNC_REVERSE_SUBTRACT);
     break;

      case 'm': case 'M':
     /* The minimum of each component is computed, as
      *  [min(1, 0), min(1, 0), min(0, 1)] which equates to (0, 0, 0).
      *  This will produce a black square on the yellow background.
      */
     glBlendEquation(GL_MIN);
     break;

      case 'x': case 'X':
     /* The minimum of each component is computed, as
      *  [max(1, 0), max(1, 0), max(0, 1)] which equates to (1, 1, 1)
      *  This will produce a white square on the yellow background.
      */
     glBlendEquation(GL_MAX);
     break;

      case 27:
         exit(0);
   }

   glutPostRedisplay();
}

/*  Main Loop
 *  Open window with initial window size, title bar,
 *  RGBA display mode, and handle input events.
 */
int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize(512,512);
   glutInitWindowPosition(100, 100);
   glutCreateWindow(argv[0]);
   init();
   glutReshapeFunc(reshape);
   glutKeyboardFunc(keyboard);
   glutDisplayFunc(display);
   glutMainLoop();
   return 0;
}

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