SDL is a library for writing 2D and 3D crossplatform games and applications. glGo uses SDL for the 2D board display, the SDL Mixer sound system as alternative to OpenAL and a couple of supportive tasks like loading and rescaling images. The SDL 3D functions are not directly used.
The 2D SDL board offers an alternative display for users who prefer the classic top-down 2D view like known from other clients or have trouble getting the 3D display working. The 2D boards looks very similar to the gGo Java board, which is intentional, and is very fast even on old computers.
There are two types of fonts available for the SDL board: A fixed 8x8 font and scaled true-type fonts. The true-type fonts look much better but render slightly slower than the fixed font. The fixed font is displayed very fast and has a good quality, but 8x8 can get too small if the board window is large. The scaled font will always have an adjusted size so the letters of SGF marks or the coordinates will fit to the stone and board size.