pick.c

计算机图形学～想必是很多人需要的～在此共享一下

/* pick.c    */

/* E. Angel, Interactive Computer Graphics */
/* A Top-Down Approach with OpenGL, Third Edition */
/* Addison-Wesley Longman, 2003 */

/* demonstrates picking used selection mode */

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


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

void drawObjects(GLenum mode)
{
	if(mode == GL_SELECT) glLoadName(1);
	glColor3f(1.0, 0.0, 0.0);
	glRectf(-0.5, -0.5, 1.0, 1.0);
	if(mode == GL_SELECT) glLoadName(2);
	glColor3f(0.0, 0.0, 1.0);
	glRectf(-1.0, -1.0, 0.5, 0.5);
}

void display()
{
	glClear(GL_COLOR_BUFFER_BIT);
	drawObjects(GL_RENDER);
	glFlush();
}

/*  processHits prints out the contents of the 
 *  selection array.
 */
void processHits (GLint hits, GLuint buffer[])
{
   unsigned int i, j;
   GLuint ii, jj, names, *ptr;

   printf ("hits = %d\n", hits);
   ptr = (GLuint *) buffer; 
   for (i = 0; i < hits; i++) {	/*  for each hit  */
      names = *ptr;
	  ptr+=3;
      for (j = 0; j < names; j++) { /*  for each name */
         if(*ptr==1) printf ("red rectangle\n");
         else printf ("blue rectangle\n");
         ptr++;
      }
      printf ("\n");
   }
}

#define SIZE 512

void mouse(int button, int state, int x, int y)
{
   GLuint selectBuf[SIZE];
   GLint hits;
   GLint viewport[4];

   if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) 
   {
   glGetIntegerv (GL_VIEWPORT, viewport);

   glSelectBuffer (SIZE, selectBuf);
   glRenderMode(GL_SELECT);

   glInitNames();
   glPushName(0);

   glMatrixMode (GL_PROJECTION);
   glPushMatrix ();
   glLoadIdentity ();
/*  create 5x5 pixel picking region near cursor location	*/
   gluPickMatrix ((GLdouble) x, (GLdouble) (viewport[3] - y), 
                  5.0, 5.0, viewport);
   gluOrtho2D (-2.0, 2.0, -2.0, 2.0);
   drawObjects(GL_SELECT);


   glMatrixMode (GL_PROJECTION);
   glPopMatrix ();
   glFlush ();

   hits = glRenderMode (GL_RENDER);
   processHits (hits, selectBuf);

   glutPostRedisplay();
   }
} 


void reshape(int w, int h)
{
   glViewport(0, 0, w, h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   gluOrtho2D (-2.0, 2.0, -2.0, 2.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
}

void keyboard(unsigned char key, int x, int y)
{
   switch (key) {
      case 27:
         exit(0);
         break;
   }
}

/* Main Loop */
int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize (500, 500);
   glutInitWindowPosition (100, 100);
   glutCreateWindow (argv[0]);
   init ();
   glutReshapeFunc (reshape);
   glutDisplayFunc(display); 
   glutMouseFunc (mouse);
   glutKeyboardFunc (keyboard);
   glutMainLoop();
   return 0; 
}