The SDL2 Video API is split into several orthogonal parts, see https://wiki.libsdl.org/MigrationGuide#Video.
As SDL and SDL2 define the same symbols, only one of the two versions can be used. configure checks for SDL2 and SDL, preferring SDL2 if both are available.
The sdl-display op is duplicated as sdl2-display, applying the necessary changes.
The sdl-draw example is a straight port from SDL to SDL2.