You can use unrpyc and unrpa to get the code and look through it, it's mostly not shaders but images, text styles, fonts, gibberish text lines, etc. I think there is also some distortion and discoloration effects in some cases too, called/enabled from scripts. I don't know ren'py so maybe they are built in into it, I'm not sure. I didn't read much and I deleted the files when my curiosity was satisfied.