按照OpenGL官方资源的说法，在任何一个语言的OpenGL实现里，截切平面的数量都不应该少于6个. 但是在我的程序里多于六个的切平面却没有效果了。

后来看到gl.h里面对GL_CLIP_PLANE是这样定义的：
#define GL_CLIP_PLANE0                0x3000
#define GL_CLIP_PLANE1                0x3001
#define GL_CLIP_PLANE2                0x3002
#define GL_CLIP_PLANE3                0x3003
#define GL_CLIP_PLANE4                0x3004
#define GL_CLIP_PLANE5                0x3005
也就是说地址为从0x3000到0x3005
用glGetIntegerv(GL_MAX_CLIP_PLANES, &x) (x是GLint类型)明明看到数量很多很多，但是为什么从0x3005之后的地址都没效果了呢？

以下是我的代码，截切平面只对灰色的球起作用

#include <stdio.h>
#include <GL/glut.h>
//Just like setup() in Processing. But it doesn't support drawing inside.
//If want to draw a static picture,
void init(int w, int h)
{

 
    float ratio = 1.0 * w / h;
    glClearColor(1.0, 1.0, 1.0, 0.0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glViewport(0, 0, w, h);
    gluPerspective(45,ratio,1,1000);
}
float angle=0.0;
GLdouble plane0Eq[4] = {0.2, 0.3, 0.4, 0};
void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
    glPushMatrix();
    glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
    glEnable(GL_BLEND);
        glRotatef(angle,angle,angle,0.0);             
        glClipPlane(0x3006, plane0Eq); //把这儿改成0x3000到0x3005，就能看到灰球被切了一半。下面的也得改
        glEnable(0x3006);
            glColor4f(0.2, 0.2, 0.2, 0.4);
            glutSolidSphere(1.4, 40, 40);
        glDisable(0x3006);
        glColor3f(0.3, 0.3, 0.3);
        glutWireSphere(1.4, 40, 40);
    glDisable(GL_BLEND);
    glPopMatrix();
    glutSwapBuffers();
    angle+=0.1;
}

void changeSize(int w, int h) {
    if(h == 0) h = 1;
    float ratio = 1.0* w / h;
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

 
    glViewport(0, 0, w, h);
    gluPerspective(45,ratio,1,1000);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt( 0.0,  0.0,  5.0,
           0.0,  0.0, -1.0,
          0.0f, 1.0f, 0.0f);
}
int main(int argc, char** argv)
{
    int width = 300;
    int height = 300;

 
    glutInit(&argc,argv); // Passes from ARGC & ARGV
    glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(width, height);
    glutInitWindowPosition(100,100);
    glutCreateWindow("Clipping");
    glutDisplayFunc(display);
    glutIdleFunc(display);
    glutReshapeFunc(changeSize);
    init(width, height);
    glutMainLoop();
}

然后是Linux的shell脚本

#!/bin/sh
gcc -o glexec gltest.c -lX11 -lGL -lGLU -lglut
./glexec

[ 本帖最后由 MarvinTau 于 2010-5-21 17:38 编辑 ]