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Improved SDL_PollEvent usage (#4794)

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* Avoid unnecessary SDL_PumpEvents calls in SDL_WaitEventTimeout

* Add a sentinel event to avoid infinite poll loops

* Move SDL_POLLSENTINEL to new internal event category

* Tweak documentation to indicate SDL_PumpEvents isn't always called

* Avoid shadowing event variable

* Ignore poll sentinel if more (user) events have been added after

Co-authored-by: Sam Lantinga <slouken@libsdl.org>
This commit is contained in:
Brick
2021-10-15 06:26:10 +01:00
committed by GitHub
parent 43da35b567
commit 8bf32e12d8
3 changed files with 52 additions and 3 deletions
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9
include/SDL_events.h
View File

@@ -160,6 +160,9 @@ typedef enum
SDL_RENDER_TARGETS_RESET = 0x2000, /**< The render targets have been reset and their contents need to be updated */
SDL_RENDER_DEVICE_RESET, /**< The device has been reset and all textures need to be recreated */
/* Internal events */
SDL_POLLSENTINEL = 0x7F00, /**< Signals the end of an event poll cycle */
/** Events ::SDL_USEREVENT through ::SDL_LASTEVENT are for your use,
* and should be allocated with SDL_RegisterEvents()
*/
@@ -798,7 +801,7 @@ extern DECLSPEC void SDLCALL SDL_FlushEvents(Uint32 minType, Uint32 maxType);
* If `event` is NULL, it simply returns 1 if there is an event in the queue,
* but will not remove it from the queue.
*
* As this function implicitly calls SDL_PumpEvents(), you can only call this
* As this function may implicitly call SDL_PumpEvents(), you can only call this
* function in the thread that set the video mode.
*
* SDL_PollEvent() is the favored way of receiving system events since it can
@@ -838,7 +841,7 @@ extern DECLSPEC int SDLCALL SDL_PollEvent(SDL_Event * event);
* If `event` is not NULL, the next event is removed from the queue and stored
* in the SDL_Event structure pointed to by `event`.
*
* As this function implicitly calls SDL_PumpEvents(), you can only call this
* As this function may implicitly call SDL_PumpEvents(), you can only call this
* function in the thread that initialized the video subsystem.
*
* \param event the SDL_Event structure to be filled in with the next event
@@ -859,7 +862,7 @@ extern DECLSPEC int SDLCALL SDL_WaitEvent(SDL_Event * event);
* If `event` is not NULL, the next event is removed from the queue and stored
* in the SDL_Event structure pointed to by `event`.
*
* As this function implicitly calls SDL_PumpEvents(), you can only call this
* As this function may implicitly call SDL_PumpEvents(), you can only call this
* function in the thread that initialized the video subsystem.
*
* \param event the SDL_Event structure to be filled in with the next event

16
include/SDL_hints.h
View File

@@ -958,6 +958,22 @@ extern "C" {
*/
#define SDL_HINT_ORIENTATIONS "SDL_IOS_ORIENTATIONS"
/**
* \brief A variable controlling the use of a sentinel event when polling the event queue
*
* This variable can be set to the following values:
* "0" - Disable poll sentinels
* "1" - Enable poll sentinels
*
* When polling for events, SDL_PumpEvents is used to gather new events from devices.
* If a device keeps producing new events between calls to SDL_PumpEvents, a poll loop will
* become stuck until the new events stop.
* This is most noticable when moving a high frequency mouse.
*
* By default, poll sentinels are enabled.
*/
#define SDL_HINT_POLL_SENTINEL "SDL_POLL_SENTINEL"
/**
* \brief Override for SDL_GetPreferredLocales()
*