Shader bug update

I made another shader today. Nothing that interesting as it's a variation on one I'd done before, but as I added it I uncommented out a line in the game which I must have disabled while trying to fix the shader bug two weeks ago. And the bug re-appeared. Thankfully as I knew it was a shader bug and knew the last change I'd done it was easy to undo, but it was surprising as I thought I'd fixed it in the shader code.

Two more screenshots

Two more screenshots, showing two different levels, in the much improved inverted colour scheme. I still haven't decided how to use this, so am alternating between it and the normal, light lines on a dark background, mode to make sure it works as well and get some idea of how to fit it in. Currently they are the second and fourth levels; early levels which accounts for the simple colour schemes.