opengl中使用两个PBO进行纹理更新，哪位大神懂？

opengl中使用两个PBO进行纹理更新，内存中的像素数据怎么也更新不进去，哪位大神懂？

glewinit();

 glGenBuffersARB(2, pboIds);

 glBindBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB, pboIds[0]);glBufferDataARB(GL_PIXEL_UNPACK_BUFFER_ARB, DATA_SIZE, 0, GL_STREAM_DRAW_ARB);

glBindBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB, pboIds[1]);

 glBufferDataARB(GL_PIXEL_UNPACK_BUFFER_ARB, DATA_SIZE, 0, GL_STREAM_DRAW_ARB);

 glBindBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB, 0);

static int index = 0;

 int nextIndex = 0; 

index = (index + 1) % 2;

nextIndex = (index + 1) % 2;

glBindTexture(GL_TEXTURE_2D, textureId);

glBindBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB, pboIds[index]);

glBindBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB, pboIds[nextIndex]);

glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, WIDTH, HEIGHT,

                GL_BGRA, GL_UNSIGNED_BYTE, 0);

glBufferDataARB(GL_PIXEL_UNPACK_BUFFER_ARB, DATA_SIZE, 0, GL_STREAM_DRAW_ARB);



GLubyte* ptr = (GLubyte*)glMapBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB, GL_WRITE_ONLY_ARB);

if(ptr){

*******//getedata();

}

glBindBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB, 0);glGenTextures(1, &textureId);

    glBindTexture(GL_TEXTURE_2D, textureId);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, IMAGE_WIDTH, IMAGE_HEIGHT, 0, PIXEL_FORMAT, GL_UNSIGNED_BYTE, (GLvoid*)imageData);

    glBindTexture(GL_TEXTURE_2D, 0);

其中imagedata是内容为空的指针，用glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, WIDTH, HEIGHT,
GL_BGRA, GL_UNSIGNED_BYTE, 0);更新纹理数据， if （ptr）｛｝中我是使用了MF GDI获取桌面试试图像，然后把桌面图像从内存DC中保存到ptr中，这样做的结果就是显示不出来图像 也就是会所数据根本没更新到纹理内存中，，，，我觉得主要问题应该在if ptr中，这里我把ptr当成一个普通的内存指针用，不知道这样可以么？有大神懂么 求解答。分不够可以加 求解答啊求解答