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Improved SDL_PollEvent usage #4794

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merged 7 commits into from Oct 15, 2021
Merged

Improved SDL_PollEvent usage #4794

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52be3e6
Avoid unnecessary SDL_PumpEvents calls in SDL_WaitEventTimeout
0x1F9F1 Sep 29, 2021
5317182
Add a sentinel event to avoid infinite poll loops
0x1F9F1 Sep 29, 2021
ee20f65
Move SDL_POLLSENTINEL to new internal event category
0x1F9F1 Sep 29, 2021
4ef44bb
Tweak documentation to indicate SDL_PumpEvents isn't always called
0x1F9F1 Sep 29, 2021
df80091
Avoid shadowing event variable
0x1F9F1 Sep 30, 2021
bf46ebf
Ignore poll sentinel if more (user) events have been added after
0x1F9F1 Oct 3, 2021
cc58e5c
Merge branch 'main' into better_poll_cycle
slouken Oct 15, 2021
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4 changes: 2 additions & 2 deletions src/events/SDL_events.c
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Expand Up @@ -887,9 +887,9 @@ SDL_WaitEventTimeout(SDL_Event * event, int timeout)
case 0:
break;
default:
/* Check whether we have reached the end of the poll cycle */
/* Check whether we have reached the end of the poll cycle, and no more events are left */
if (timeout == 0 && event && event->type == SDL_POLLSENTINEL) {
return 0;
return SDL_PeepEvents(event, 1, SDL_GETEVENT, SDL_FIRSTEVENT, SDL_LASTEVENT) == 1;
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After searching through GitHub for uses of SDL_PollEvent, there is an alarming amount of strange/incorrect usage (mostly in beginner projects), such as:

  • Only calling it once per frame
  • Not checking the return value
  • Calling SDL_PollEvent(NULL) in a loop
  • Polling until a certain event (i.e a key press), and pushing the rest back into the queue

I'd say those first 3 issues are broken by design, but the last one (and similar uses of user-added events inside a poll cycle) could be an issue, so I decided it's better to err on the side of caution and ignore the sentinel if there are still more events in the queue.

}
/* Has existing events */
return 1;
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