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emscripten: Respect SDL_HINT_MAIN_CALLBACK_RATE.

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Fixes #13345.
This commit is contained in:
Ryan C. Gordon
2025-07-15 15:48:22 -04:00
parent 1b65f25465
commit b3af72f69e
2 changed files with 73 additions and 7 deletions
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67
src/main/emscripten/SDL_sysmain_callbacks.c
View File

@@ -24,9 +24,61 @@
#include <emscripten.h>
// For Emscripten, we let you use SDL_HINT_MAIN_CALLBACK_RATE, because it might be useful to drop it super-low for
// things like loopwave that don't really do much but wait on the audio device, but be warned that browser timers
// are super-unreliable in modern times, so you likely won't hit your desired callback rate with good precision.
// Almost all apps should leave this alone, so we can use requestAnimationFrame, which is intended to run reliably
// at the refresh rate of the user's display.
static Uint32 callback_rate_increment = 0;
static bool iterate_after_waitevent = false;
static bool callback_rate_changed = false;
static void SDLCALL MainCallbackRateHintChanged(void *userdata, const char *name, const char *oldValue, const char *newValue)
{
callback_rate_changed = true;
iterate_after_waitevent = newValue && (SDL_strcmp(newValue, "waitevent") == 0);
if (iterate_after_waitevent) {
callback_rate_increment = 0;
} else {
const double callback_rate = newValue ? SDL_atof(newValue) : 0.0;
if (callback_rate > 0.0) {
callback_rate_increment = (Uint32) SDL_NS_TO_MS((double) SDL_NS_PER_SECOND / callback_rate);
} else {
callback_rate_increment = 0;
}
}
}
// just tell us when any new event is pushed on the queue, so we can check a flag for "waitevent" mode.
static bool saw_new_event = false;
static bool SDLCALL EmscriptenMainCallbackEventWatcher(void *userdata, SDL_Event *event)
{
saw_new_event = true;
return true;
}
static void EmscriptenInternalMainloop(void)
{
const SDL_AppResult rc = SDL_IterateMainCallbacks(true);
// callback rate changed? Update emscripten's mainloop iteration speed.
if (callback_rate_changed) {
callback_rate_changed = false;
if (callback_rate_increment == 0) {
emscripten_set_main_loop_timing(EM_TIMING_RAF, 1);
} else {
emscripten_set_main_loop_timing(EM_TIMING_SETTIMEOUT, callback_rate_increment);
}
}
if (iterate_after_waitevent) {
SDL_PumpEvents();
if (!saw_new_event) {
// do nothing yet. Note that we're still going to iterate here because we can't block,
// but we can stop the app's iteration from progressing until there's an event.
return;
}
saw_new_event = false;
}
const SDL_AppResult rc = SDL_IterateMainCallbacks(!iterate_after_waitevent);
if (rc != SDL_APP_CONTINUE) {
SDL_QuitMainCallbacks(rc);
emscripten_cancel_main_loop(); // kill" the mainloop, so it stops calling back into it.
@@ -36,9 +88,18 @@ static void EmscriptenInternalMainloop(void)
int SDL_EnterAppMainCallbacks(int argc, char *argv[], SDL_AppInit_func appinit, SDL_AppIterate_func appiter, SDL_AppEvent_func appevent, SDL_AppQuit_func appquit)
{
const SDL_AppResult rc = SDL_InitMainCallbacks(argc, argv, appinit, appiter, appevent, appquit);
SDL_AppResult rc = SDL_InitMainCallbacks(argc, argv, appinit, appiter, appevent, appquit);
if (rc == SDL_APP_CONTINUE) {
emscripten_set_main_loop(EmscriptenInternalMainloop, 0, 0); // run at refresh rate, don't throw an exception since we do an orderly return.
if (!SDL_AddEventWatch(EmscriptenMainCallbackEventWatcher, NULL)) {
rc = SDL_APP_FAILURE;
} else {
SDL_AddHintCallback(SDL_HINT_MAIN_CALLBACK_RATE, MainCallbackRateHintChanged, NULL);
callback_rate_changed = false;
emscripten_set_main_loop(EmscriptenInternalMainloop, 0, 0); // don't throw an exception since we do an orderly return.
if (callback_rate_increment > 0.0) {
emscripten_set_main_loop_timing(EM_TIMING_SETTIMEOUT, callback_rate_increment);
}
}
} else {
SDL_QuitMainCallbacks(rc);
}

13
src/video/emscripten/SDL_emscriptenopengles.c
View File

@@ -28,6 +28,7 @@
#include "SDL_emscriptenvideo.h"
#include "SDL_emscriptenopengles.h"
#include "../../main/SDL_main_callbacks.h"
bool Emscripten_GLES_LoadLibrary(SDL_VideoDevice *_this, const char *path)
{
@@ -50,10 +51,14 @@ bool Emscripten_GLES_SetSwapInterval(SDL_VideoDevice *_this, int interval)
}
if (Emscripten_ShouldSetSwapInterval(interval)) {
if (interval == 0) {
emscripten_set_main_loop_timing(EM_TIMING_SETTIMEOUT, 0);
} else {
emscripten_set_main_loop_timing(EM_TIMING_RAF, interval);
// don't change the mainloop timing if the app is also driving a main callback with this hint,
// as we assume that was the more deliberate action.
if (!SDL_HasMainCallbacks() || !SDL_GetHint(SDL_HINT_MAIN_CALLBACK_RATE)) {
if (interval == 0) {
emscripten_set_main_loop_timing(EM_TIMING_SETTIMEOUT, 0);
} else {
emscripten_set_main_loop_timing(EM_TIMING_RAF, interval);
}
}
}