events: Periodically poll tray events on *nix platforms

Tray events on *nix platforms usually run over DBus, and the events subsequently aren't delivered via the window event queue. As a result, SDL_WaitEvent() won't unblock when tray events arrive, particularly if there is no currently active window.

Wake up periodically to poll when tray items are active to avoid blocking the delivery and processing of tray events.

src/events/SDL_events.c

@@ -43,6 +43,10 @@
 #include "../video/android/SDL_androidevents.h"
 #endif
 
+#ifdef SDL_PLATFORM_UNIX
+#include "../tray/SDL_tray_utils.h"
+#endif
+
 // An arbitrary limit so we don't have unbounded growth
 #define SDL_MAX_QUEUED_EVENTS 65535
 
@@ -52,6 +56,9 @@
 // Determines how often to pump events if joysticks or sensors are actively being read
 #define EVENT_POLL_INTERVAL_NS SDL_MS_TO_NS(1)
 
+// Determines how often to pump events if tray items are active
+#define TRAY_POLL_INTERVAL_NS SDL_MS_TO_NS(50)
+
 // Make sure the type in the SDL_Event aligns properly across the union
 SDL_COMPILE_TIME_ASSERT(SDL_Event_type, sizeof(Uint32) == sizeof(SDL_EventType));
 
@@ -1531,6 +1538,12 @@ static Sint64 SDL_events_get_polling_interval(void)
     }
 #endif
 
+#ifdef SDL_PLATFORM_UNIX
+    if (SDL_HasActiveTrays()) {
+        // Tray events on *nix platforms run separately from window system events, and need periodic polling
+        poll_intervalNS = SDL_min(poll_intervalNS, TRAY_POLL_INTERVAL_NS);
+    }
+#endif
     return poll_intervalNS;
 }