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Created attachment 4275 [details]
Patch to src/joystick/hidapi/SDL_hidapi_switch.c which applies to SDL2 2.0.12

I've noticed that the Switch Pro Controller hidapi driver does not report battery levels when connected via Bluetooth, despite having code for setting joystick->epowerlevel.

This is caused by the driver always using k_eSwitchInputReportIDs_SimpleControllerState via Bluetooth. Using that mode means that the state reports you get back from the controller do not include battery state. Not using the full controller state over Bluetooth effectively makes this driver's support for setting joystick->epowerlevel entirely pointless, only ever reporting SDL_JOYSTICK_POWER_WIRED.

Is there a reason this was set to only use SimpleControllerState via Bluetooth?

I've attached a patch I'm using to allow getting battery level for the Switch Pro Controller.

A couple notes about this patch:
1) It changes LoadStickCalibration to accept the input_mode that is selected, because that's really what should determine what is used for stick extents, since stick extents differ between the modes.
2) In my patch I only use FullControllerState when the vid/pid matches the official Switch Pro Controller, as a cautionary measure in case some third-party controllers have problems with FullControllerState mode via Bluetooth (I noticed a HORI Wireless Switch Pad I had seemed to not read controller calibration correctly for stick extents. Maybe it's calibration data was uninitialized on account of having never been used with a Switch? I'm unsure, though if that guess is right maybe SDL2 should be detecting an uninitiated calibration state and using some sensible defaults)