The best way to know how to help you is to know what your plans are. The way the shader is set up is pretty simple, but if you don't have much GM experience, having a plan first can go a long way to getting you on the right track.
Sure. Let's say I want to do a Dither effect like in the last screenshot. In which event should I enter the code? Should all lines go into the draw_gui event? Thanks for your help.
