Created attachment 4327 [details]
SDL_JoystickSetLED

Attached is a patch to expose an API for setting the color of an LED on a joystick. The main (and admittedly, only) example is the light bar found on the PS4 and PS5 controllers.

Currently, there are only two ways to access the light bar:

- Steam Input
- `chmod`ing /sys/class/leds/ manually, then writing directly to userspace files:

https://github.com/FNA-XNA/FNA/blob/master/src/FNAPlatform/SDL2_FNAPlatform.cs#L2679

It's ugly, unreliable, either platform-specific or store-specific, and kind of pointless to do now that we're directly accessing the device via hidapi anyhow.

Some games using the above hack include Transistor, FEZ, TowerFall, Mercenary Kings, Dust: An Elysian Tail, Apotheon, and probably more that I've forgotten about over the years. Luckily they all use it behind FNA's SetLightBarEXT extension, so updating SDL and using this new function resolves the hack without actually touching the games themselves.

Just about the only thing I'm unsure about is the way we send the LED packet - it reuses the Rumble call, which feels a bit odd to me, but it looks like SDL_hidapi_rumble.c handles it pretty gracefully, so it may not be as bad as it looks.

Example program below!

--------------------------------------------------------------------------------

#include "SDL.h"

int main(int argc, char **argv)
{
	SDL_Window *window;
	SDL_Renderer *renderer;
	SDL_GameController *controller;
	SDL_Event evt;
	Uint8 r, g, b;
	int x, y;
	Uint8 run = 1;

	SDL_Init(SDL_INIT_VIDEO | SDL_INIT_GAMECONTROLLER);

	SDL_CreateWindowAndRenderer(
		640,
		480,
		SDL_WINDOW_SHOWN,
		&window,
		&renderer
	);
	controller = SDL_GameControllerOpen(0);
	
	while (run)
	{
		while (SDL_PollEvent(&evt) > 0)
		{
			if (evt.type == SDL_QUIT)
			{
				run = 0;
			}
		}

		SDL_GetMouseState(&x, &y);
		r = (Uint8) ((x / 640.0f) * 255);
		b = (Uint8) ((x / 480.0f) * 255);
		g = r + b / 2;

		SDL_GameControllerSetLED(controller, r, g, b);
		SDL_SetRenderDrawColor(renderer, r, g, b, 0xFF);
		SDL_RenderClear(renderer);
		SDL_RenderPresent(renderer);
	}

	SDL_GameControllerClose(controller);
	SDL_DestroyRenderer(renderer);
	SDL_DestroyWindow(window);
	SDL_Quit();
}