Use SDL2.0.
SMP.
Move GL code into Backend.
Bones mutex.
Load Textures in GL thread.
Avoid unnecessary Fog changes.
Delete Texures from GL thread.
Rework Bones mutex.
Use fewer static vars.
Cull bone code.
Embed BoneCalc()
Make BoneCalc() re-entrant.
SDL 1.2 or 2.0