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：

/*
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* All Rights Reserved
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* FITNESS FOR A PARTICULAR PURPOSE.  IN NO EVENT SHALL SILICON
* GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT,
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* OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION, LOSS OF
* PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF THIRD
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* 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  Unpublished - rights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
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*
* 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;
}