The USE_SDL variable is used to autoconfigure the dependencies for ports which use an SDL based library like devel/sdl12 and x11-toolkits/sdl_gui.
The following SDL libraries are recognized at the moment:
sdl: devel/sdl12
gfx: graphics/sdl_gfx
gui: x11-toolkits/sdl_gui
image: graphics/sdl_image
ldbad: devel/sdl_ldbad
mixer: audio/sdl_mixer
mm: devel/sdlmm
net: net/sdl_net
sound: audio/sdl_sound
ttf: graphics/sdl_ttf
Therefore, if a port has a dependency on net/sdl_net and audio/sdl_mixer, the syntax will be:
USE_SDL= net mixer
The dependency devel/sdl12, which is required by net/sdl_net and audio/sdl_mixer, is automatically added as well.
If you use USE_SDL, it will automatically:
Add a dependency on sdl12-config to BUILD_DEPENDS
Add the variable SDL_CONFIG to CONFIGURE_ENV
Add the dependencies of the selected libraries to the LIB_DEPENDS
To check whether an SDL library is available, you can do it with the WANT_SDL variable:
WANT_SDL= yes
.include <bsd.port.pre.mk>
.if ${HAVE_SDL:Mmixer}!=""
USE_SDL+= mixer
.endif
.include <bsd.port.post.mk>