DRAFT |
SDL_HINT_EMSCRIPTEN_ASYNCIFY
A hint that specifies if SDL should give back control to the browser automatically when running with asyncify.
Values
0 |
disable emscripten_sleep calls (if you give back browser control manually or use asyncify for other purposes) |
1 |
enable emscripten_sleep calls (the default) |
Default
SDL pauses the application and gives back control to the browser automatically when the application is compiled with asyncify support, by calling emscripten_sleep when:
- refreshing the software graphics context,
- refreshing the GPU graphics context,
using SDL_Delay,
polling events (through SDL_Delay), hence supporting SDL_WaitEvent
The SDL application hence can be ported to the web browser without any code change to the main loop (no emscripten_set_main_loop), at the cost of a reasonable performance hit.
Code Examples
To disable the default behavior:
SDL_SetHint(SDL_HINT_EMSCRIPTEN_ASYNCIFY, "0");
//...
SDL_Init(SDL_INIT_EVERYTHING);
With the default SDL_HINT_EMSCRIPTEN_ASYNCIFY=1, to optimize performance, you'll typically want to make asyncify only instrument functions in the call path:
emcc ... -s ASYNCIFY=1 -s ASYNCIFY_WHITELIST='["main", "call_path_to_your_main_loop", "SDL_WaitEvent", "SDL_WaitEventTimeout", "SDL_Delay", "SDL_RenderPresent", "GLES2_RenderPresent", "SDL_GL_SwapWindow", "Emscripten_GLES_SwapWindow", "byn$$fpcast-emu$$Emscripten_GLES_SwapWindow", "SDL_UpdateWindowSurface", "SDL_UpdateWindowSurfaceRects", "Emscripten_UpdateWindowFramebuffer"]'
Remarks
This hint only applies to the Emscripten platform.
Version
This hint is available since SDL2 port version_21 / Emscripten 1.39.14, and is not merged in the official SDL repository yet.
