I didn’t checked all possible use cases of GLSL Hacker (a huge and actually impossible task) and some sequences of drawing instructions (render calls) can generate OpenGL errors. So if you suspect something dodgy because the rendering is not what you expect, you can check the OpenGL errors after some particular instructions.
Do you know that you can use data structures as uniform variables in GLSL?
Today, a small code sample (in Lua) that shows how to use the mouse to put where you want on the screen a letter with random parameters (position, scaling, orientation and color).
Since version 0.8.0, GLSL Hacker comes with a new plugin based on FreeType-GL, that allows to load any TTF (True Type Font) or OTF (Open Type Font) font file. I also added a Lua layer in GLSL Hacker libs folder to make font management even easier (libs/lua/gx_font.lua).