ping pong between same framebuffer two color attachments

Question

In order to optimize I'm trying to set up a setup which ping pong between same framebuffer two color attachments to apply some postprocess effects. It seems to work (effects are applied) but concurently I'm getting a lot of strange artifacts like:

• blinking squares
• borders on depth discontinuities
• color spilling on screen (window resize removes it)

Which change or disappear partly when I for example remove one step (one post process effect) from "ping ponging".

If I do this ordinary way using different framebuffers seems to remove them but I'm not 100% sure if it is not a mess in the shaders or something but they seem fine.

In each frame I'm doing ping pong like that:

First step - render to current color attach using other fb texture

fbDeferredLighting->bindFramebuffer(); //fb which has two color attachments
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
effect1->setConstPerFrameUniforms();
//get 0 attachment from fb scene prepass to apply effect and draw on fbDeferredLighting current color attach
effect1->setTextureUniforms(fbScene, 0); 
quad->draw();

And then repeating some number of times: swap step and drawing, using same fb swapped attachment:

fbDeferredLighting->bindFramebuffer();
//after swap - now current=1, other=0 or current=0, other=1
std::swap(colorAttachment0Current, colorAttachment0Other);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texturesDiffuse[colorAttachment0Current]->getTextureID(), 0);
glClear(GL_DEPTH_BUFFER_BIT); //only clear depth
effectX->setConstPerFrameUniforms();
//get other color attach and use it to apply effect on current
effectX->setTextureUniforms(fbDeferredLighting , colorAttachment0Other); 
quad->draw();

Is this correct?

EDIT: I wonder, maybe rewrite it to compute shaders, that would simplify things.

Answer 1

Actually, GL_COLOR_BUFFER_BIT also need to be cleared

After creation of the framebuffer, draw buffer need to be set to:

glDrawBuffer(GL_COLOR_ATTACHMENT0);

and then after each swap:

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

instead of only

glClear(GL_DEPTH_BUFFER_BIT);

To clear current attachment 0. I don't really understand these clearing bits extensively but this seems to fix blinking "chess board" artifact.

Borders seems to be connected with motion blur shader.