SDL_gfx Library.

SDL graphics drawing  primitives  and other support functions. The
SDL_gfx  library  evolved  out of the SDL_gfxPrimitives code which
provided basic drawing routines such as lines, circles or polygons
and SDL_rotozoom which  implemented a interpolating rotozoomer for
SDL surfaces.

homepage: http://www.ferzkopp.net/Software/SDL_gfx-2.0/