Troubleshooting OpenGL ES 1.1 textures on the iPhone

I'm trying to draw a texture into an offscreen framebuffer, and its rende开发者_如何学Pythonrbuffer always ends up completely blank (black). The weird thing is, I know the context is set up, and I'm checking for errors using glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES) and glGetError(), but neither function says anything is wrong. Are there any other error-checking functions I can call which might shed some light on what's happening?

Difficult to give you a precise answer without more information. Perhaps could you post some code about your setup and usage of the render buffer?

In the meantime, here is some info about how to properly setup an offscreen framebuffer:

// Remember the FBO being used for the display framebuffer
glGetIntegerv(GL_FRAMEBUFFER_BINDING_OES, (GLint *)&SystemFBO);

// Create the texture and the FBO for offscreen frame buffer
glGenTextures(1, &ResultTexture);
glBindTexture(GL_TEXTURE_2D, ResultTexture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glGenFramebuffersOES(1, &ResultFBO);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, ResultFBO);
glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, ResultTexture, 0);

glBindFramebufferOES(GL_FRAMEBUFFER_OES, ResultFBO);

// do your rendering to offscreen framebuffer
...

// restore original frame buffer object
glBindFramebufferOES(GL_FRAMEBUFFER_OES, SystemFBO);

// use ResultTexture as usual
glBindTexture(GL_TEXTURE_2D, ResultTexture);

Hope this helps...