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Bug 2548

Summary: Cannot poll joystick button when window is not in focus
Product: SDL Reporter: Alan <aychen>
Component: joystickAssignee: Ryan C. Gordon <icculus>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 CC: aychen, icculus
Version: 2.0.3   
Hardware: x86   
OS: Mac OS X 10.8   

Description Alan 2014-05-16 20:07:32 UTC 
I'm running an interface that uses both joysticks and keyboard.  

For the joysticks, I'm polling the axes, hats, and buttons.  I use SDL_JoystickEventState(SDL_DISABLE) to turn off the joystick events and then I run SDL_JoystickUpdate() to poll the joystick values. 

For the keyboard, I'm using SDL_PollEvent(&event) to search for keystroke events after I've created a window.  

What I've noticed is that when the window is not in focus, the buttons for the joystick no longer work.  The hat and axes still work.  Oddly enough, if I don't ever call SDL_PollEvent, then the joystick button works when the window is not in focus. 

Thank you,
Alan
Comment 1 Ryan C. Gordon 2014-05-19 00:50:53 UTC 
(In reply to Alan from comment #0)
> What I've noticed is that when the window is not in focus, the buttons for
> the joystick no longer work.  The hat and axes still work.  Oddly enough, if
> I don't ever call SDL_PollEvent, then the joystick button works when the
> window is not in focus. 

Not giving joystick events when an SDL window doesn't have focus is intentional (although I would argue incorrect) behavior.

Never calling SDL_PollEvent() "works" because SDL doesn't know the window lost focus until the OS event queue is processed, which happens under SDL_PollEvent(), even if the OS has already taken focus from the window.

I'm surprised you get hat and axes events, though; they should be protected by the same check as the buttons.

Anyhow, to get joystick events even if the window doesn't have focus, call this sometime after SDL_Init()...

    SDL_SetHint(SDL_HINT_JOYSTICK_ALLOW_BACKGROUND_EVENTS, "1");

(That probably fixes your concern, but I'm marking this bug ASSIGNED for now, so I can see why the hats and axes still come through.)

--ryan.
Comment 2 Alan 2014-05-19 16:22:22 UTC 
Hey Ryan, 

That worked great, thank you. 

Alan
Comment 3 Sam Lantinga 2014-06-22 04:31:41 UTC 
I fixed the bug where you got axis and hat events if the application didn't have focus.
https://hg.libsdl.org/SDL/rev/8e09eceea61e