Batch controller axis events for reduced CPU usage on Steam Link

app/streaming/input.cpp

@@ -652,11 +652,15 @@ Uint32 SdlInputHandler::mouseMoveTimerCallback(Uint32 interval, void *param)
 
 void SdlInputHandler::handleControllerAxisEvent(SDL_ControllerAxisEvent* event)
 {
-    GamepadState* state = findStateForGamepad(event->which);
+    SDL_JoystickID gameControllerId = event->which;
+    GamepadState* state = findStateForGamepad(gameControllerId);
     if (state == NULL) {
         return;
     }
 
+    // Batch all pending axis motion events for this gamepad to save CPU time
+    SDL_Event nextEvent;
+    for (;;) {
         switch (event->axis)
         {
             case SDL_CONTROLLER_AXIS_LEFTX:
@@ -689,6 +693,21 @@ void SdlInputHandler::handleControllerAxisEvent(SDL_ControllerAxisEvent* event)
                 return;
         }
 
+        // Check for another event to batch with
+        if (SDL_PeepEvents(&nextEvent, 1, SDL_PEEKEVENT, SDL_CONTROLLERAXISMOTION, SDL_CONTROLLERAXISMOTION) <= 0) {
+            break;
+        }
+
+        event = &nextEvent.caxis;
+        if (event->which != gameControllerId) {
+            // Stop batching if a different gamepad interrupts us
+            break;
+        }
+
+        // Remove the next event to batch
+        SDL_PeepEvents(&nextEvent, 1, SDL_GETEVENT, SDL_CONTROLLERAXISMOTION, SDL_CONTROLLERAXISMOTION);
+    }
+
     sendGamepadState(state);
 }