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- # Emscripten
-
- (This documentation is not very robust; we will update and expand this later.)
-
- ## A quick note about audio
-
- Modern web browsers will not permit web pages to produce sound before the
- user has interacted with them; this is for several reasons, not the least
- of which being that no one likes when a random browser tab suddenly starts
- making noise and the user has to scramble to figure out which and silence
- it.
-
- To solve this, most browsers will refuse to let a web app use the audio
- subsystem at all before the user has interacted with (clicked on) the page
- in a meaningful way. SDL-based apps also have to deal with this problem; if
- the user hasn't interacted with the page, SDL_OpenAudioDevice will fail.
-
- There are two reasonable ways to deal with this: if you are writing some
- sort of media player thing, where the user expects there to be a volume
- control when you mouseover the canvas, just default that control to a muted
- state; if the user clicks on the control to unmute it, on this first click,
- open the audio device. This allows the media to play at start, the user can
- reasonably opt-in to listening, and you never get access denied to the audio
- device.
-
- Many games do not have this sort of UI, and are more rigid about starting
- audio along with everything else at the start of the process. For these, your
- best bet is to write a little Javascript that puts up a "Click here to play!"
- UI, and upon the user clicking, remove that UI and then call the Emscripten
- app's main() function. As far as the application knows, the audio device was
- available to be opened as soon as the program started, and since this magic
- happens in a little Javascript, you don't have to change your C/C++ code at
- all to make it happen.
-
- Please see the discussion at https://github.com/libsdl-org/SDL/issues/6385
- for some Javascript code to steal for this approach.
-
-
- ## Building SDL/emscripten
-
- SDL currently requires at least Emscripten 2.0.32 to build. Newer versions
- are likely to work, as well.
-
-
- Build:
-
- $ mkdir build
- $ cd build
- $ emconfigure ../configure --host=asmjs-unknown-emscripten --disable-assembly --disable-threads --disable-cpuinfo CFLAGS="-O2"
- $ emmake make
-
- Or with cmake:
-
- $ mkdir build
- $ cd build
- $ emcmake cmake ..
- $ emmake make
-
- To build one of the tests:
-
- $ cd test/
- $ emcc -O2 --js-opts 0 -g4 testdraw2.c -I../include ../build/.libs/libSDL2.a ../build/libSDL2_test.a -o a.html
-
- Uses GLES2 renderer or software
-
- Some other SDL2 libraries can be easily built (assuming SDL2 is installed somewhere):
-
- SDL_mixer (http://www.libsdl.org/projects/SDL_mixer/):
-
- $ EMCONFIGURE_JS=1 emconfigure ../configure
- build as usual...
-
- SDL_gfx (http://cms.ferzkopp.net/index.php/software/13-sdl-gfx):
-
- $ EMCONFIGURE_JS=1 emconfigure ../configure --disable-mmx
- build as usual...
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