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