Applying shader to blitting for line-by-line processing of a texture


I am trying to process a texture line by line in the fastest way possible using a fragment shader (think shader based 1D Cellular Automata)


So the idea is to read from line N and write to line N+1. The problem is that because both lines belong to the same texture, I get the infamous feedback loop warning/error although I tried to scissor and setViewport to line N+1 in hopes that the write-unaffected pixels of line N would become available. Nope.

I’m trying to avoid the buffer swap tricks and would like to know the leanest way of doing this in threejs.
Ideally WebGLRenderer.copyTextureToTexture but with fragment shader applied.