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emscripten: dedupe keyboard event listeners across multiple windows

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This commit is contained in:
Vittorio Romeo
2026-05-05 01:54:29 +02:00
committed by Sam Lantinga
parent 2bb6df90ad
commit 7f03da9588
1 changed files with 22 additions and 0 deletions
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22
src/video/emscripten/SDL_emscriptenevents.c
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@@ -1341,11 +1341,33 @@ void Emscripten_RegisterEventHandlers(SDL_WindowData *data)
keyElement = Emscripten_GetKeyboardTargetElement(data->keyboard_element);
if (keyElement) {
// Emscripten's HTML5 helpers do not deduplicate `addEventListener` calls:
// see `registerOrRemoveHandler` in `emscripten/src/lib/libhtml5.js`.
//
// If a previous SDL window already registered keyboard handlers on the same
// target, the new registration would *stack* a second listener, causing every
// browser keydown to fire `Emscripten_HandleKey` twice.
//
// The duplicate calls then produce two `SDL_EVENT_KEY_DOWN` events per physical
// keypress (the second one with `repeat=true`, due to the keystate-based repeat
// detection in `SDL_SendKeyboardKeyInternal`).
//
// We must clear any prior handler on this target before installing ours:
emscripten_set_keydown_callback(keyElement, NULL, 0, NULL);
emscripten_set_keyup_callback(keyElement, NULL, 0, NULL);
emscripten_set_keypress_callback(keyElement, NULL, 0, NULL);
MAIN_THREAD_EM_ASM_INT({
var data = $0;
// our keymod state can get confused in various ways (changed capslock when browser didn't have focus, etc), and you can't query the current
// state from the DOM, outside of a keyboard event, so catch keypresses globally and reset mod state if it's unexpectedly wrong. Best we can do.
// Note that this thing _only_ adjusts the lock keys if necessary; the real SDL keypress handling happens elsewhere.
// Remove any prior listener first -- `addEventListener` does not deduplicate either.
if (document.sdlEventHandlerLockKeysCheck) {
document.removeEventListener("keydown", document.sdlEventHandlerLockKeysCheck);
}
document.sdlEventHandlerLockKeysCheck = function(event) {
// don't try to adjust the state on the actual lock key presses; the normal key handler will catch that and adjust.
if ((event.key != "CapsLock") && (event.key != "NumLock") && (event.key != "ScrollLock"))