glClipPlane裁剪平面

(2012-02-21 12:49:18)

转载▼

1. void glClipPlane(GLenum plane, const GLdouble *equation); 

    定义一个裁剪平面。equation参数指向平面方程Ax + By + Cz + D = 0的4个系数。equation=（0，-1，0,0），前三个参数（0，-1,0）可以理解为法线向下，只有向下的，即Y<0的才能显示，最后一个参数0表示从z=0平面开始。这样就是裁剪掉上半平面。相应的equation=（0,1,0,0）表示裁剪掉下半平面，equation=（1,0,0,0）表示裁剪掉左半平面，equation=（-1,0,0,0）表示裁剪掉右半平面，equation=（0,0,-1,0）表示裁剪掉前半平面，equation=（0,0,1,0）表示裁剪掉后半平面

裁剪平面的代码例子

示例3-5是经过两个裁剪平面裁剪的线框球体，裁去了3/4体积，如图3-23所示。

图3-23 裁剪后的线框球体

示例程序3-5 经过两个裁剪平面裁剪的线框球体：clip.c

1. void init(void)
2. {
3. glClearColor(0.0,0.0,0.0,0.0);
4. glShadeModel(GL_FLAT);
5. }
6. void display(void)
7. {
8. GLdouble eqn [4]={0.0,1.0,0.0,0.0};
9. GLdouble eqn2 [4] ={1.0,0.0,0.0,0.0};
10. glClear(GL_COLOR_BUFFER_BIT);
11. glColor3f(1.0,1.0,1.0);
12. glPushMatrix();
13. glTranslatef(0.0,0.0,-5.0);
14. glClipPlane(GL_CLIP_PLANE0,eqn);
15. glEnable(GL_CLIP_PLANE0);
16. glClipPlane(GL_CLIP_PLANE1,eqn2);
17. glEnable(GL_CLIP_PLANE1);
18. glRotatef(90.0,1.0,0.0,0.0);
19. glutWireSphere(1.0,20,16);
20. glPopMatrix();
21. glFlush();
22. }
23. void reshape(int w,int h)
24. {
25. glViewport(0,0,(GLsizei)w,(GLsizei)h);
26. glMatrixMode(GL_PROJECTION);
27. glLoadIdentity();
28. gluPerspective(60.0,(GLfloat)w/(GLfloat)h,1.0,20.0);
29. glMatrixMode(GL_MODELVIEW);
30. }
31. int main(int argc,char**argv)
32. {
33. glutInit(&argc,argv);
34. glutInitDisplayMode(GLUT_SINGLE |GLUT_RGB);
35. glutInitWindowSize(500,500);
36. glutInitWindowPosition(100,100);
37. glutCreateWindow(argv [0]);
38. init();
39. glutDisplayFunc(display);
40. glutReshapeFunc(reshape);
41. glutMainLoop();
42. return 0;
43. }