问题
I'm trying to copy vertex data from a texture to a vertex buffer, and then draw the vertex buffer. As far as I know the best way to do this is to bind the texture to a fbo, and use glReadPixels to copy it to a vbo. However, I can't seem to get this working: glReadPixels fails with the error "invalid operation".
Corrections, examples and alternate methods welcome. :)
Here's the relevant code:
glEnable(GL_TEXTURE_2D)
w, h = 32, 32
vbo = glGenBuffers(1)
glBindBuffer(GL_ARRAY_BUFFER, vbo)
glBufferData(GL_ARRAY_BUFFER, sizeof(c_float)*w*h*4, None, GL_STREAM_COPY)
glBindBuffer(GL_ARRAY_BUFFER, 0)
fbo = glGenFramebuffersEXT(1)
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo)
tex = glGenTextures(1)
glBindTexture(GL_TEXTURE_2D, tex)
# tex params here
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, w, h, 0, GL_RGBA, GL_FLOAT, None)
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, tex, 0)
assert glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT) == 36053
glReadBuffer(GL_COLOR_ATTACHMENT0_EXT)
glBindBuffer(GL_PIXEL_PACK_BUFFER, vbo)
glReadPixels(0, 0, w, h, GL_RGBA, GL_FLOAT, None) # invalid operation?
回答1:
I've solved the issue myself.
The last argument to ReadPixels is used as an offset instead of a pointer in this case, and is not automatically cast by pyopengl, use:
glReadPixels(0, 0, w, h, GL_RGBA, GL_FLOAT, c_void_p(0)) # works!
来源：https://stackoverflow.com/questions/5755478/implementing-render-to-vertex-array-glreadpixels-fails-invalid-operation