Is there a convenient method of doing a translucent overlay allowing you to dim out what you've already rendered, then draw "normal" stuff on top. My scenario is, I have drawn the game screen, but want to mask it out, still allowing it to be somewhat visible, while placing emphasis on a popup.
I should point out that I'm still using immediate mode, more or less - my 2D engine uses GL.DrawArrays for everything. I know I could probably draw a solid box blended over the scene, but while I'm sort of evil by still using immediate mode, I'm not so evil as to resort to drawing with primitives or GL.Begin/GL.End.
So... is there any way of doing this without using primitives? I guess you could use a shader, but I haven't even began to look at these, and I assume it won't work on GL.DrawArray commands that have already been executed. I also read that OpenGL has lighting built into it which sounds kind of cool, but again I haven't researched this yet either.
Any advice appreciated :)