gluUnProject glUnProject4包含w值 glProject求取屏幕z坐标

1.gluUnProject传入OGL屏幕坐标值，产生世界坐标系中的值，经过ViewPort矩阵，Project矩阵，Model-View矩阵的逆变换得到。gluUnProject个参数中的值见OGL文档，其中winY值需要将窗口坐标系转换为OGL左下角的屏幕坐标系才能得到。winZ值需要已知物体世界坐标系中的z值经过glProject变换得到，才能获得屏幕中点击物体的正确世界坐标系值。

2.变换矩阵用glGetIntegerv查询获得(无论是固定管线，还是Shader可编程管线)。

GLint viewport[4];
GLdouble mvmatrix[16], projmatrix[16];

glGetIntegerv (GL_VIEWPORT, viewport);
glGetDoublev (GL_MODELVIEW_MATRIX, mvmatrix);
glGetDoublev (GL_PROJECTION_MATRIX, projmatrix);

实例代码：

/* * Copyright (c) 1993-2003, Silicon Graphics, Inc. * All Rights Reserved * * Permission to use, copy, modify, and distribute this software for any * purpose and without fee is hereby granted, provided that the above * copyright notice appear in all copies and that both the copyright * notice and this permission notice appear in supporting documentation, * and that the name of Silicon Graphics, Inc. not be used in * advertising or publicity pertaining to distribution of the software * without specific, written prior permission. * * THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU "AS-IS" AND * WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR OTHERWISE, * INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY OR * FITNESS FOR A PARTICULAR PURPOSE.  IN NO EVENT SHALL SILICON * GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT, * SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND, * OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION, LOSS OF * PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF THIRD * PARTIES, WHETHER OR NOT SILICON GRAPHICS, INC.  HAS BEEN ADVISED OF * THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON ANY THEORY OF * LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE POSSESSION, USE * OR PERFORMANCE OF THIS SOFTWARE. * * US Government Users Restricted Rights  * Use, duplication, or disclosure by the Government is subject to * restrictions set forth in FAR 52.227.19(c)(2) or subparagraph * (c)(1)(ii) of the Rights in Technical Data and Computer Software * clause at DFARS 252.227-7013 and/or in similar or successor clauses * in the FAR or the DOD or NASA FAR Supplement.  Unpublished - rights * reserved under the copyright laws of the United States. * * Contractor/manufacturer is: *Silicon Graphics, Inc. *1500 Crittenden Lane *Mountain View, CA  94043 *United State of America * * OpenGL(R) is a registered trademark of Silicon Graphics, Inc. *//* *  unproject.c *  When the left mouse button is pressed, this program  *  reads the mouse position and determines two 3D points  *  from which it was transformed.  Very little is displayed. */#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;}