Enable joystick events in background

Capture the gamepads even when the window is not focused.

Note: In theory, with this flag set, we could capture gamepad events
even without a window (--no-window). In practice, scrcpy still requires
a window, because --no-window implies --no-control, and the input
manager is owned by the sc_screen instance, which does not exist if
there is no window. Supporting this use case would require a lot of
refactors.

Refs <#5270 (comment)>
PR #5270 <#5270>

Suggested-by: Luiz Henrique Laurini <luizhenriquelaurini@gmail.com>

app/src/scrcpy.c

@@ -136,6 +136,10 @@ sdl_set_hints(const char *render_driver) {
     if (!SDL_SetHint(SDL_HINT_VIDEO_MINIMIZE_ON_FOCUS_LOSS, "0")) {
         LOGW("Could not disable minimize on focus loss");
     }
+
+    if (!SDL_SetHint(SDL_HINT_JOYSTICK_ALLOW_BACKGROUND_EVENTS, "1")) {
+        LOGW("Could not allow joystick background events");
+    }
 }
 
 static void

app/src/usb/scrcpy_otg.c

@@ -58,6 +58,10 @@ scrcpy_otg(struct scrcpy_options *options) {
         LOGW("Could not enable linear filtering");
     }
 
+    if (!SDL_SetHint(SDL_HINT_JOYSTICK_ALLOW_BACKGROUND_EVENTS, "1")) {
+        LOGW("Could not allow joystick background events");
+    }
+
     // Minimal SDL initialization
     if (SDL_Init(SDL_INIT_EVENTS)) {
         LOGE("Could not initialize SDL: %s", SDL_GetError());