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;
}