#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;
}