Possible game controller event bug in SDL2.0.3

SDL Development
1

Hi all, I’d appreciate some help with this issue I’ve encountered in SDL 2.0.3 with game controller events. The issue is that after disconnecting and reconnecting a game controller, subsequent events generated for that controller have the wrong joystick index. This appears to be a bug, but it’s possible I’ve misunderstood something. Assistance would be appreciated.

Reproduction steps:

  1. Connect a game controller and start the application, or connect a game controller while running the application (both cases produce the same result).
  2. Handle the event SDL_CONTROLLERDEVICEADDED and note the joystick device index given by SDL_Event::cdevice.which.
  3. Generate input events by using the device (such as SDL_CONTROLLERBUTTONDOWN) and note the joystick device index given by (for example) SDL_Event::cbutton.which. Observe that the index matches the one noted in step 2.
  4. Disconnect the device.
  5. Handle the event SDL_CONTROLLERDEVICEREMOVED and note the joystick device index given by SDL_Event::cdevice.which.
  6. Reconnect the device.
  7. Handle the event SDL_CONTROLLERDEVICEADDED and note the joystick device index given by SDL_Event::cdevice.which.
  8. Generate input events by using the device (such as SDL_CONTROLLERBUTTONDOWN) and note the joystick device index given by (for example) SDL_Event::cbutton.which. Observe that the index does not match the one noted in step 7.

Thanks in advance.

2

Also, I should point out that I’ve so far only tested this on Windows, in case the issue is platform-specific.

3

OK, I believe I’ve solved the issue and it looks like it was indeed in my understanding. This is a gotcha that might help anyone else getting started with SDL game controllers.

The “which” member in the relevant event structure has a different meaning for SDL_CONTROLLERDEVICEADDED than for SDL_CONTROLLERDEVICEREMOVED and controller input events such as SDL_CONTROLLERBUTTONDOWN. For SDL_CONTROLLERDEVICEADDED, it describes an index into the list of active devices, not the actual joystick ID (SDL_JoystickInstanceID) which is the meaning of the value for those other events.

4

The “which” member in the relevant event structure has a different
meaning for SDL_CONTROLLERDEVICEADDED than for
SDL_CONTROLLERDEVICEREMOVED and controller input events such as
SDL_CONTROLLERBUTTONDOWN. For SDL_CONTROLLERDEVICEADDED, it describes an
index into the list of active devices, not the actual joystick ID
(SDL_JoystickInstanceID) which is the meaning of the value for those
other events.

We should document this better (and probably change the API for 2.1 to
be more clear)…it’s a very common misunderstanding.

–ryan.