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README-emscripten: corrected comments about vsync.

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Ryan C. Gordon
2025-12-16 12:23:45 -05:00
parent ef0a604d44
commit 9022d90e01
1 changed files with 9 additions and 6 deletions
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docs/README-emscripten.md
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@@ -210,12 +210,15 @@ Calling SDL_RenderPresent (or SDL_GL_SwapWindow) will not actually
present anything on the screen until your return from your mainloop
function.
Note that on other platforms, SDL will default to vsync _off_ in the 2D render
API. Since changing this will affect how the mainloop runs, the 2D render API
will only change vsync settings if explicitly requested by the app, either
with SDL_PROP_RENDERER_CREATE_PRESENT_VSYNC_NUMBER, or calling
SDL_SetRenderVSync(). Otherwise it will default to whatever the Emscripten
mainloop is set to use via emscripten_set_main_loop().
Note that SDL attempts to default to vsync _off_ on all platforms. You almost
certainly do _not_ want this in Emscripten, however, as it will affect the
efficiency of the mainloop. If using OpenGL directly, you should call
SDL_GL_SetSwapInterval(1) sometime near startup; if using the 2D render API,
either create the renderer with with the property
SDL_PROP_RENDERER_CREATE_PRESENT_VSYNC_NUMBER set to 1, or call
SDL_SetRenderVSync(renderer, 1). If you don't explicitly set vsync, you'll get
a higher (but perhaps unstable) framerate, and use more power, but it will
still work. Choosing a vsync of 1 will use requestAnimationFrame if possible.
If you're using the SDL main callbacks, the mainloop defaults to using
requestAnimationFrame (effectively vsync), because it calls