... Also, I have to say that at first I thought it would be a "Royal
Pain" to have to deal with rendering 2d stuff in openGL - but it
actually turned out to be much easier than I thought and kind of a lot
of fun (although I may have more pain later I suppose). The only thing
that isn't trivially simple, in my opinion, is figuring out how you
want to deal with texture size limitations. In particular, on the
majority of systems out there, textures have to be a power-of-2 in
width and height - so you have to deal with that to upload say a 24x12
image for blitting. The 3 basic approaches are:
1. overallocate textures and render just the portion of the texture
that has an image (so that 24x12 image would be on a 32x16 texture and
would render just texcoords (.0,.0)-(.75,.75)), which will waste about
50% of your video memory and possibly cause extra texture thrashing,
but actually some commercial games ship this way cause it just never
ended up being a problem for their game.
2. spread images across multiple textures and draw all of them (so the
24x12 image would be spread across 4 textures, a 16x8, an 8x8, a 16x4
and an 8x4) which lets you draw more polys in order to not waste so
much video memory
3. pack multiple images into a single texture - the attached example
uses that approach. It can be pathologically bad in terms of memory
thrashing in some cases (like say if you wanted to draw one image each
from 100 large multi-image textures) but if images that are used
together are in a texture together, it is actually the optimal
approach in terms of performance (like it tends to be good to make
sure font characters are all packed in textures together)