mirror of
https://github.com/Ryujinx/SDL.git
synced 2024-12-22 18:55:42 +00:00
Ryan C. Gordon
parent
8ad043fc38
commit
bd77b9a0ce
|
|
@ -1,8 +1,172 @@
|
|||
# Emscripten
|
||||
|
||||
(This documentation is not very robust; we will update and expand this later.)
|
||||
## The state of things
|
||||
|
||||
## A quick note about audio
|
||||
(As of September 2023, but things move quickly and we don't update this
|
||||
document often.)
|
||||
|
||||
In modern times, all the browsers you probably care about (Chrome, Firefox,
|
||||
Edge, and Safari, on Windows, macOS, Linux, iOS and Android), support some
|
||||
reasonable base configurations:
|
||||
|
||||
- WebAssembly (don't bother with asm.js any more)
|
||||
- WebGL (which will look like OpenGL ES 2 or 3 to your app).
|
||||
- Threads (see caveats, though!)
|
||||
- Game controllers
|
||||
- Autoupdating (so you can assume they have a recent version of the browser)
|
||||
|
||||
All this to say we're at the point where you don't have to make a lot of
|
||||
concessions to get even a fairly complex SDL-based game up and running.
|
||||
|
||||
|
||||
## RTFM
|
||||
|
||||
This document is a quick rundown of some high-level details. The
|
||||
documentation at [emscripten.org](https://emscripten.org/) is vast
|
||||
and extremely detailed for a wide variety of topics, and you should at
|
||||
least skim through it at some point.
|
||||
|
||||
|
||||
## Porting your app to Emscripten
|
||||
|
||||
Many many things just need some simple adjustments and they'll compile
|
||||
like any other C/C++ code, as long as SDL was handling the platform-specific
|
||||
work for your program.
|
||||
|
||||
First, you probably need this in at least one of your source files:
|
||||
|
||||
```c
|
||||
#ifdef __EMSCRIPTEN__
|
||||
#include <emscripten.h>
|
||||
#endif
|
||||
```
|
||||
|
||||
Second: assembly language code has to go. Replace it with C. You can even use
|
||||
[x86 SIMD intrinsic functions in Emscripten](https://emscripten.org/docs/porting/simd.html)!
|
||||
|
||||
Third: Middleware has to go. If you have a third-party library you link
|
||||
against, you either need an Emscripten port of it, or the source code to it
|
||||
to compile yourself, or you need to remove it.
|
||||
|
||||
Fourth: You still start in a function called main(), but you need to get out of
|
||||
it and into a function that gets called repeatedly, and returns quickly,
|
||||
called a mainloop.
|
||||
|
||||
Somewhere in your program, you probably have something that looks like a more
|
||||
complicated version of this:
|
||||
|
||||
```c
|
||||
void main(void)
|
||||
{
|
||||
initialize_the_game();
|
||||
while (game_is_still_running) {
|
||||
check_for_new_input();
|
||||
think_about_stuff();
|
||||
draw_the_next_frame();
|
||||
}
|
||||
deinitialize_the_game();
|
||||
}
|
||||
```
|
||||
|
||||
This will not work on Emscripten, because the main thread needs to be free
|
||||
to do stuff and can't sit in this loop forever. So Emscripten lets you set up
|
||||
a [mainloop](https://emscripten.org/docs/porting/emscripten-runtime-environment.html#browser-main-loop).
|
||||
|
||||
```c
|
||||
static void mainloop(void) /* this will run often, possibly at the monitor's refresh rate */
|
||||
{
|
||||
if (!game_is_still_running) {
|
||||
deinitialize_the_game();
|
||||
#ifdef __EMSCRIPTEN__
|
||||
emscripten_cancel_main_loop(); /* this should "kill" the app. */
|
||||
#else
|
||||
exit(0);
|
||||
#endif
|
||||
}
|
||||
|
||||
check_for_new_input();
|
||||
think_about_stuff();
|
||||
draw_the_next_frame();
|
||||
}
|
||||
|
||||
void main(void)
|
||||
{
|
||||
initialize_the_game();
|
||||
#ifdef __EMSCRIPTEN__
|
||||
emscripten_set_main_loop(mainloop, 0, 1);
|
||||
#else
|
||||
while (1) { mainloop(); }
|
||||
#endif
|
||||
}
|
||||
```
|
||||
|
||||
Basically, `emscripten_set_main_loop(mainloop, 0, 1);` says "run
|
||||
`mainloop` over and over until I end the program." The function will
|
||||
run, and return, freeing the main thread for other tasks, and then
|
||||
run again when it's time. The `1` parameter does some magic to make
|
||||
your main() function end immediately; this is useful because you
|
||||
don't want any shutdown code that might be sitting below this code
|
||||
to actually run if main() were to continue on, since we're just
|
||||
getting started.
|
||||
|
||||
There's a lot of little details that are beyond the scope of this
|
||||
document, but that's the biggest intial set of hurdles to porting
|
||||
your app to the web.
|
||||
|
||||
|
||||
## Do you need threads?
|
||||
|
||||
If you plan to use threads, they work on all major browsers now. HOWEVER,
|
||||
they bring with them a lot of careful considerations. Rendering _must_
|
||||
be done on the main thread. This is a general guideline for many
|
||||
platforms, but a hard requirement on the web.
|
||||
|
||||
Many other things also must happen on the main thread; often times SDL
|
||||
and Emscripten make efforts to "proxy" work to the main thread that
|
||||
must be there, but you have to be careful (and read more detailed
|
||||
documentation than this for the finer points).
|
||||
|
||||
Even when using threads, your main thread needs to set an Emscripten
|
||||
mainloop that runs quickly and returns, or things will fail to work
|
||||
correctly. More on this later.
|
||||
|
||||
You should definitely read [Emscripten's pthreads docs](https://emscripten.org/docs/porting/pthreads.html)
|
||||
for all the finer points. Mostly SDL's thread API will work as expected,
|
||||
but is built on pthreads, so it shares the same little incompatibilities
|
||||
that are documented there, such as where you can use a mutex, and when
|
||||
a thread will start running, etc.
|
||||
|
||||
|
||||
IMPORTANT: You have to decide to either build something that uses
|
||||
threads or something that doesn't; you can't have one build
|
||||
that works everywhere. This is an Emscripten (or maybe WebAssembly?
|
||||
Or just web browsers in general?) limitation. If you aren't using
|
||||
threads, it's easier to not enable them at all, at build time.
|
||||
|
||||
If you use threads, you _have to_ run from a web server that has
|
||||
[COOP/COEP headers set correctly](https://web.dev/why-coop-coep/)
|
||||
or your program will fail to start at all.
|
||||
|
||||
If building with threads, `__EMSCRIPTEN_PTHREADS__` will be defined
|
||||
for checking with the C preprocessor, so you can build something
|
||||
different depending on what sort of build you're compiling.
|
||||
|
||||
|
||||
## Audio
|
||||
|
||||
Audio works as expected at the API level, but not exactly like other
|
||||
platforms.
|
||||
|
||||
You'll only see a single default audio device. Audio capture also works;
|
||||
if the browser pops up a prompt to ask for permission to access the
|
||||
microphone, the SDL_OpenAudioDevice call will succeed and start producing
|
||||
silence at a regular interval. Once the user approves the request, real
|
||||
audio data will flow. If the user denies it, the app is not informed and
|
||||
will just continue to receive silence.
|
||||
|
||||
SDL3 allows you to open the audio device at any time; it'll just throw away
|
||||
audio data until the user interacts with the page, and then start feeding
|
||||
the browser seamlessly, but for SDL2, you need to manage this yourself.
|
||||
|
||||
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
|
||||
|
|
@ -35,42 +199,141 @@ 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.
|
||||
|
||||
SDL3 allows you to open the audio device at any time; it'll just throw away
|
||||
audio data until the user interacts with the page, and then start feeding
|
||||
the browser seamlessly, but for SDL2, you need to manage this yourself.
|
||||
|
||||
|
||||
## Rendering
|
||||
|
||||
If you use SDL's 2D render API, it will use GLES2 internally, which
|
||||
Emscripten will turn into WebGL calls. You can also use OpenGL ES 2
|
||||
directly by creating a GL context and drawing into it.
|
||||
|
||||
Calling SDL_RenderPresent (or SDL_GL_SwapWindow) will not actually
|
||||
present anything on the screen until your return from your mainloop
|
||||
function.
|
||||
|
||||
|
||||
## Building SDL/emscripten
|
||||
|
||||
First: do you _really_ need to build SDL from source?
|
||||
|
||||
If you aren't developing SDL itself, have a desire to mess with its source
|
||||
code, or need something on the bleeding edge, don't build SDL. Just use
|
||||
Emscripten's packaged version!
|
||||
|
||||
Compile and link your app with `-s USE_SDL=2` and it'll use a build of
|
||||
SDL packaged with Emscripten. This comes from the same source code and
|
||||
fixes the Emscripten project makes to SDL are generally merged into SDL's
|
||||
revision control, so often this is much easier for app developers.
|
||||
|
||||
`-s USE_SDL=1` will select Emscripten's JavaScript reimplementation of SDL
|
||||
1.2 instead; if you need SDL 1.2, this might be fine, but we generally
|
||||
recommend you don't use SDL 1.2 in modern times.
|
||||
|
||||
|
||||
If you want to build SDL, though...
|
||||
|
||||
SDL currently requires at least Emscripten 3.1.35 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
|
||||
This works on Linux/Unix and macOS. Please send comments about Windows.
|
||||
|
||||
Make sure you've [installed emsdk](https://emscripten.org/docs/getting_started/downloads.html)
|
||||
first, and run `source emsdk_env.sh` at the command line so it finds the
|
||||
tools.
|
||||
|
||||
(These configure options might be overkill, but this has worked for me.)
|
||||
|
||||
```bash
|
||||
cd SDL
|
||||
mkdir build
|
||||
cd build
|
||||
emconfigure ../configure --host=wasm32-unknown-emscripten --disable-pthreads --disable-assembly --disable-cpuinfo CFLAGS="-s USE_SDL=0 -O3"
|
||||
emmake make -j4
|
||||
```
|
||||
|
||||
If you want to build with thread support, something like this works:
|
||||
|
||||
```bash
|
||||
emconfigure ../configure --host=wasm32-unknown-emscripten --enable-pthreads --disable-assembly --disable-cpuinfo CFLAGS="-s USE_SDL=0 -O3 -pthread" LDFLAGS="-pthread"
|
||||
```
|
||||
|
||||
Or with cmake:
|
||||
|
||||
$ mkdir build
|
||||
$ cd build
|
||||
$ emcmake cmake ..
|
||||
$ emmake make
|
||||
```bash
|
||||
mkdir build
|
||||
cd build
|
||||
emcmake cmake ..
|
||||
emmake make -j4
|
||||
```
|
||||
|
||||
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
|
||||
```bash
|
||||
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
|
||||
## Building your app
|
||||
|
||||
Some other SDL2 libraries can be easily built (assuming SDL2 is installed somewhere):
|
||||
You need to compile with `emcc` instead of `gcc` or `clang` or whatever, but
|
||||
mostly it uses the same command line arguments as Clang.
|
||||
|
||||
SDL_mixer (http://www.libsdl.org/projects/SDL_mixer/):
|
||||
Link against the SDL/build/.libs/libSDL2.a file you generated by building SDL,
|
||||
link with `-s USE_SDL=2` to use Emscripten's prepackaged SDL2 build.
|
||||
|
||||
Usually you would produce a binary like this:
|
||||
|
||||
```bash
|
||||
gcc -o mygame mygame.c # or whatever
|
||||
```
|
||||
|
||||
But for Emscripten, you want to output something else:
|
||||
|
||||
```bash
|
||||
gcc -o index.html mygame.c # or whatever
|
||||
```
|
||||
|
||||
This will produce several files...support Javascript and WebAssembly (.wasm)
|
||||
files. The `-o index.html` will produce a simple HTML page that loads and
|
||||
runs your app. You will (probably) eventually want to replace or customize
|
||||
that file and do `-o index.js` instead to just build the code pieces.
|
||||
|
||||
If you're working on a program of any serious size, you'll likely need to
|
||||
link with `-s ALLOW_MEMORY_GROWTH=1 -s MAXIMUM_MEMORY=1gb` to get access
|
||||
to more memory. If using pthreads, you'll need the `-s MAXIMUM_MEMORY=1gb`
|
||||
or the app will fail to start on iOS browsers, but this might be a bug that
|
||||
goes away in the future.
|
||||
|
||||
|
||||
|
||||
## Debugging
|
||||
|
||||
Debugging web apps is a mixed bag. You should compile and link with
|
||||
`-gsource-map`, which embeds a ton of source-level debugging information into
|
||||
the build, and make sure _the app source code is available on the web server_,
|
||||
which is often a scary proposition for various reasons.
|
||||
|
||||
When you debug from the browser's tools and hit a breakpoint, you can step
|
||||
through the actual C/C++ source code, though, which can be nice.
|
||||
|
||||
If you try debugging in Firefox and it doesn't work well for no apparent
|
||||
reason, try Chrome, and vice-versa. Sometimes it's just like that.
|
||||
|
||||
SDL_Log() will write to the Javascript console, and honestly I find
|
||||
printf-style debugging to be easier than setting up a build for proper
|
||||
debugging, so use whatever tools work best for you.
|
||||
|
||||
|
||||
## Questions?
|
||||
|
||||
Please give us feedback on this document at [the SDL bug tracker](https://github.com/libsdl-org/SDL/issues).
|
||||
If something is wrong or unclear, we want to know!
|
||||
|
||||
$ 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...
|
||||
|
|
|
|||
Loading…
Reference in a new issue