OpenGL 获取当前屏幕坐标对应的三维坐标

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

void display(void)
{

   glClear(GL_COLOR_BUFFER_BIT);
   glFlush();
}

/* Change these values for a different transformation  */
void reshape(int w, int h)
{
   glViewport (0, 0, (GLsizei) w, (GLsizei) h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   gluPerspective (45.0, (GLfloat) w/(GLfloat) h, 1.0, 100.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
}

void mouse(int button, int state, int x, int y)
{
   GLint viewport[4];
   GLdouble mvmatrix[16], projmatrix[16];
   GLint realy;  /*  OpenGL y coordinate position  */
   GLdouble wx, wy, wz;  /*  returned world x, y, z coords  */
   switch (button) {
      case GLUT_LEFT_BUTTON:
         if (state == GLUT_DOWN) {
            glGetIntegerv (GL_VIEWPORT, viewport);
            glGetDoublev (GL_MODELVIEW_MATRIX, mvmatrix);
            glGetDoublev (GL_PROJECTION_MATRIX, projmatrix);
            

/*  note viewport[3] is height of window in pixels  */
            realy = viewport[3] - (GLint) y - 1;
            printf ("Coordinates at cursor are (%4d, %4d)\n", x, realy);
            gluUnProject ((GLdouble) x, (GLdouble) realy, 0.0,
               mvmatrix, projmatrix, viewport, &wx, &wy, &wz);
            printf ("World coords at z=0.0 are (%f, %f, %f)\n",wx, wy, wz);
            gluUnProject ((GLdouble) x, (GLdouble) realy, 1.0,
               mvmatrix, projmatrix, viewport, &wx, &wy, &wz);
            printf ("World coords at z=1.0 are (%f, %f, %f)\n",wx, wy, wz);
         }
         break;
      case GLUT_RIGHT_BUTTON:
         if (state == GLUT_DOWN)
            exit(0);
         break;
      default:
         break;
   }
}

void keyboard(unsigned char key, int x, int y)
{

switch (key) {
      case 27:
         exit(0);
         break;
   }
}

/*

 *  Open window, register input callback functions

 */

int main(int argc, char** argv)
{

   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize (500, 500);
   glutInitWindowPosition (100, 100);
   glutCreateWindow (argv[0]);
   glutDisplayFunc(display);
   glutReshapeFunc(reshape);
   glutKeyboardFunc (keyboard);
   glutMouseFunc(mouse);
   glutMainLoop();
   return 0;
}