This was just a quick shader port/hack from an openFrameworks library I was working on. You can see the LUT texture generation here (which is done on the fly in oF): https://github.com/TeehanLax/ofxAsciiArt/blob/master/src/ofx...

All of this is pulled from Sol's TextFX library. The character bitmap actually doesn't line up to Sol's table, so that's why you see weird characters popping up in places. The main goal was just to get image to text working on the GPU. I've typically done it on the CPU. Over time I hope the mess gets cleaned up.