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想用用opengl在vega中画个矩形，但一直显示不了。麻烦班主和大神帮我看看是怎么回事，望指教。贴下代码：谢谢

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>                                       
#include "vg.h"            
#include "pf.h"
#include <GL/gl.h>
#pragma comment(lib, "opengl32.lib")
#pragma comment(lib, "glu32.lib")
static void Draw(vgChannel *chan, void *udata )
{
        pfPushIdentMatrix();
        glMatrixMode( GL_PROJECTION );
        glLoadIdentity();
        gluOrtho2D(-1, 1, -1, 1 );
        glMatrixMode( GL_MODELVIEW );
        pfPushIdentMatrix();
        pfPushState();
        glBegin( GL_QUADS );
glVertex3f(0.0f, 0.0f, 0.0f);
glVertex3f( 1.0f, 0.0f, 0.0f);
glVertex3f( 1.0f, 0.0f, 1.0f);
glVertex3f(0.0f, 0.0f, 1.0f);
        glEnd( );        
        pfPopMatrix();
        pfPopState ();
}

int main()
{          
        vgChannel * vgChan;      
        vgInitSys();
        vgDefineSys( "vegawin.adf" );            
        vgWindow* win = vgGetWin(0);
        //vgProp( win, VGWIN_WINBORDER, 0 );        
        vgConfigSys();
        vgChan=vgGetChan(0);
        vgAddFunc(vgChan,VGCHAN_POSTDRAW,Draw,NULL);
        while(1) {
                vgSyncFrame();
                vgFrame();
        }
        vgExit(0);
        return 0;
}

我是在channel的notify中画的矩形，供参考

1. context->pushElements(true);
   
2. 
   
3. 
   
4. // need to disable the depth buffer since it's enabled by default
   
5. vrDepthTest::Element depthTestElement;
   
6. depthTestElement.m_enable = false;
   
7. context->setElement(vrDepthTest::Element::Id, &depthTestElement);
   
8. // set up an orthographic projection.  In this case we'll just map the
   
9. // channel viewport to 0 to 1 both horizontally and vertically.
   
10. vrTransform::ElementProjection projectionElement;
    
11. projectionElement.makeOrthographic(0.0f, 1.0f, 0.0f, 1.0f, -1.0f, 1.0f);
    
12. 
    
13. glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
    
14. glEnable(GL_BLEND);
    
15. int width, height;
    
16. float hfov, vfov, aspect;
    
17. vpWindow *window = *vpWindow::begin();
    
18. assert(window);
    
19. window->getSize(&width, &height);
    
20. channel->getFOVSymmetric(&hfov, &vfov);
    
21. if (width > height)
    
22.         aspect = (float) width / (float) height;
    
23. else aspect = (float) height / (float) width;
    
24. vfov = hfov / aspect;
    
25. 
    
26. // draw a box around what the binoculars are looking at.  We'll
    
27. // compute the size of the box by computing the ratio between the
    
28. // main and binocular fields of view.
    
29. float x = 0.2;
    
30. float y = 0.1;
    
31. 
    
32. glColor4f(1.0f, 1.0f, 0.0f, 0.5f);
    
33. glBegin(GL_POLYGON);
    
34. glVertex2f(-0.7f + -x, 0.7f +  y);
    
35. glVertex2f(-0.7f + -x, 0.7f + -y);
    
36. glVertex2f(-0.7f +  x, 0.7f + -y);
    
37. glVertex2f(-0.7f +  x, 0.7f +  y);
    
38. glEnd();
    
39. 
    
40. context->setElement(vrTransform::ElementProjection::Id,
    
41.         &projectionElement);
    
42. context->popElements();

复制代码

我是在channel的notify中画的矩形，供参考

vgConfigSys();
        vgChan=vgGetChan(0);
        vgAddFunc(vgChan,VGCHAN_POSTDRAW,Draw,NULL);
次序？
vgChan=vgGetChan(0);
        vgAddFunc(vgChan,VGCHAN_POSTDRAW,Draw,NULL);
放在
vgConfigSys();前面吧