How does FBO realize nested use?

[Dark_Photon]

Continued here:

Create 2 framebuffers， But introduced a new problem: splash screen, the screen keeps flickering

what I want to do is this: Create 2 framebuffers, let’s call them fb1 and fb2. Render the scene to fb2 normally. Render fb2 to fb1 with one post-processing effect. Render fb1 to the default framebuffer (we’ll call it fb0) with another post-processing effect. This method really works. But introduced a new problem: splash screen, the screen keeps flickering. After verification: changing glFinish to glReadPixels, the flickering phenomenon still exists. But the image saved by glReadPixels is no…