BACKENDS: Fix missing mouse events when system cursor cannot be moved

Normally with SDL, a mouse motion event will be sent after the
system mouse cursor has been moved by a call to
SDL_WarpMouseInWindow, but if the system cursor cannot be moved
(e.g. because the window does not have mouse focus), games still
need to receive these mouse events so they can successfully update
the mouse position internally. Otherwise, games continue to think
the mouse is still in the original position and will continue to
try to perform whatever action is associated with that mouse
position.

Refs Trac#9689.

2 files changed, 27 insertions, 0 deletions

diff --git a/backends/events/default/default-events.cpp b/backends/events/default/default-events.cpp
index c7c39da069..667914b023 100644
--- a/backends/events/default/default-events.cpp
+++ b/backends/events/default/default-events.cpp
@@ -254,4 +254,30 @@ void DefaultEventManager::pushEvent(const Common::Event &event) {
 		_artificialEventSource.addEvent(event);
 }
 
+void DefaultEventManager::purgeMouseEvents() {
+	_dispatcher.dispatch();
+
+	Common::Queue<Common::Event> filteredQueue;
+	while (!_eventQueue.empty()) {
+		Common::Event event = _eventQueue.pop();
+		switch (event.type) {
+		case Common::EVENT_MOUSEMOVE:
+		case Common::EVENT_LBUTTONDOWN:
+		case Common::EVENT_LBUTTONUP:
+		case Common::EVENT_RBUTTONDOWN:
+		case Common::EVENT_RBUTTONUP:
+		case Common::EVENT_WHEELUP:
+		case Common::EVENT_WHEELDOWN:
+		case Common::EVENT_MBUTTONDOWN:
+		case Common::EVENT_MBUTTONUP:
+			// do nothing
+			break;
+		default:
+			filteredQueue.push(event);
+			break;
+		}
+	}
+	_eventQueue = filteredQueue;
+}
+
 #endif // !defined(DISABLE_DEFAULT_EVENTMANAGER)
diff --git a/backends/events/default/default-events.h b/backends/events/default/default-events.h
index f378fb9ff0..38406c25aa 100644
--- a/backends/events/default/default-events.h
+++ b/backends/events/default/default-events.h
@@ -80,6 +80,7 @@ public:
 	virtual void init();
 	virtual bool pollEvent(Common::Event &event);
 	virtual void pushEvent(const Common::Event &event);
+	virtual void purgeMouseEvents() override;
 
 	virtual Common::Point getMousePos() const { return _mousePos; }
 	virtual int getButtonState() const { return _buttonState; }