example-rust | Continuous Rust Fuzzing Example | Testing library

I think the flashing is caused by buffer swapping: in flashes.rs only the first buffer to be drawn into is cleared. The second one will be all zeros, or leftover gpu memory if you're unlucky. According to the OpenGL wiki there's no good way around calling graphics::clear:

A modern OpenGL program should always use double buffering. . . The buffers should always be cleared. On much older hardware, there was a technique to get away without clearing the scene, but on even semi-recent hardware, this will actually make things slower. So always do the clear.

Instead, the usual method is to accumulate your changes to a texture or renderbuffer, and then draw that to the screen, exactly as you described.

I couldn't find any way to do this from within opengl_graphics either (there are no calls to gl::GenFramebuffers anywhere in it) but it's relatively straightforward to set up using raw gl calls. (I've used textures instead of renderbuffers because they have the significant advantage of being supported by high-level methods like Image::draw.)