processing

I have a programming problem trying to make a 2D fragment shader using GLSL I'm using the programming language "processing" rather than something like C++ which makes it kind of niche for anyone unfamiliar with that language. But it's possible it could be done in Java, I will look it up. Or maybe even in pure GLSL? Anyways, I just wan't a template for how to do one pass per frame and do the next pass on the previous output, ̶i̶t̶ ̶d̶o̶e̶s̶n̶'̶t̶ ̶n̶e̶e̶d̶ ̶t̶o̶ ̶d̶o̶ ̶a̶n̶y̶t̶h̶i̶n̶g̶ ̶g̶r̶a̶p̶h̶i̶c̶a̶l̶l̶y̶ ̶f̶a̶n̶c̶y̶ but having this "persistent" canvas is very important. UPDATE: I now have a template that seems to be working. So the requirement changed a bit (and thus I might have to raise the budget a bit) I actually do need to do something "graphically fancy". Not just anything, something specific, but the specs aren't finished, and I won't award the project to anyone before I'we decided exact and final requirements. Other than that, it's still someone competent in glsl, (and processing is a plus) that I'm looking for.