Still learning Unity3d as I go- but in the OnPostRender section, I've worked out how to render an unlit texture.

firstly, I was wondeirng how I draw lines.

Pleasingly as expected, the drawing would take into account z-buffer test.

  

So now I can draw lines! So if I can draw lines, I can bring across HUD logic from C++ version, but the next thing I want to do, is to render unlit textures to this hud as well - this means I can place text or numbers.

Which is what I'm kind of doing here - in my c++ code, I build up 256 display lists for each character but as far as I can tell in Unity, displays lists aren't available, so will just have to render them in immediate mode.