I think I now the answer, but let me ask anyway
Is there a possibility to copy data between to FBOs or even between a FBO and the framebuffer? Or do I have to draw data to a FBO (which might be slower…)
I’d simply draw since that’s the simplest way. I guess it should be possible to copy with glCopyPixels() too by simply binding the color buffer you want to copy from to GL_COLOR_ATTACHMENT1_EXT on the color buffer you want to copy to and then set glDrawBuffer(GL_COLOR_ATTACHMENT0_EXT) and glReadBuffer(GL_COLOR_ATTACHMENT1_EXT).