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.

10 files changed, 80 insertions, 7 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; }
diff --git a/backends/events/sdl/sdl-events.cpp b/backends/events/sdl/sdl-events.cpp
index 6f34420674..91ca0f5df6 100644
--- a/backends/events/sdl/sdl-events.cpp
+++ b/backends/events/sdl/sdl-events.cpp
@@ -75,7 +75,7 @@ static uint32 convUTF8ToUTF32(const char *src) {
 #endif
 
 SdlEventSource::SdlEventSource()
-    : EventSource(), _scrollLock(false), _joystick(0), _lastScreenID(0), _graphicsManager(0)
+    : EventSource(), _scrollLock(false), _joystick(0), _lastScreenID(0), _graphicsManager(0), _queuedFakeMouseMove(false)
 #if SDL_VERSION_ATLEAST(2, 0, 0)
       , _queuedFakeKeyUp(false), _fakeKeyUp()
 #endif
@@ -508,6 +508,12 @@ bool SdlEventSource::pollEvent(Common::Event &event) {
 		return true;
 	}
 
+	if (_queuedFakeMouseMove) {
+		event = _fakeMouseMove;
+		_queuedFakeMouseMove = false;
+		return true;
+	}
+
 	SDL_Event ev;
 	while (SDL_PollEvent(&ev)) {
 		preprocessEvents(&ev);
@@ -1003,6 +1009,12 @@ void SdlEventSource::resetKeyboardEmulation(int16 x_max, int16 y_max) {
 	_km.joy_y = 0;
 }
 
+void SdlEventSource::fakeWarpMouse(const int x, const int y) {
+	_queuedFakeMouseMove = true;
+	_fakeMouseMove.type = Common::EVENT_MOUSEMOVE;
+	_fakeMouseMove.mouse = Common::Point(x, y);
+}
+
 bool SdlEventSource::handleResizeEvent(Common::Event &event, int w, int h) {
 	if (_graphicsManager) {
 		_graphicsManager->notifyResize(w, h);
diff --git a/backends/events/sdl/sdl-events.h b/backends/events/sdl/sdl-events.h
index 1d701f5ecf..5fd3cb7ea5 100644
--- a/backends/events/sdl/sdl-events.h
+++ b/backends/events/sdl/sdl-events.h
@@ -51,6 +51,12 @@ public:
 	 */
 	virtual void resetKeyboardEmulation(int16 x_max, int16 y_max);
 
+	/**
+	 * Emulates a mouse movement that would normally be caused by a mouse warp
+	 * of the system mouse.
+	 */
+	void fakeWarpMouse(const int x, const int y);
+
 protected:
 	/** @name Keyboard mouse emulation
 	 * Disabled by fingolfin 2004-12-18.
@@ -156,6 +162,18 @@ protected:
 	 */
 	SDLKey obtainKeycode(const SDL_keysym keySym);
 
+	/**
+	 * Whether _fakeMouseMove contains an event we need to send.
+	 */
+	bool _queuedFakeMouseMove;
+
+	/**
+	 * A fake mouse motion event sent when the graphics manager is told to warp
+	 * the mouse but the system mouse is unable to be warped (e.g. because the
+	 * window is not focused).
+	 */
+	Common::Event _fakeMouseMove;
+
 #if SDL_VERSION_ATLEAST(2, 0, 0)
 	/**
 	 * Whether _fakeKeyUp contains an event we need to send.
diff --git a/backends/graphics/sdl/sdl-graphics.cpp b/backends/graphics/sdl/sdl-graphics.cpp
index e6699df1cd..64ee9f7aa1 100644
--- a/backends/graphics/sdl/sdl-graphics.cpp
+++ b/backends/graphics/sdl/sdl-graphics.cpp
@@ -212,6 +212,13 @@ bool SdlGraphicsManager::notifyMousePosition(Common::Point &mouse) {
 	return valid;
 }
 
+void SdlGraphicsManager::setSystemMousePosition(const int x, const int y) {
+	assert(_window);
+	if (!_window->warpMouseInWindow(x, y)) {
+		_eventSource->fakeWarpMouse(x, y);
+	}
+}
+
 void SdlGraphicsManager::handleResizeImpl(const int width, const int height) {
 	_eventSource->resetKeyboardEmulation(width - 1, height - 1);
 	_forceRedraw = true;
diff --git a/backends/graphics/sdl/sdl-graphics.h b/backends/graphics/sdl/sdl-graphics.h
index 993a1c3db6..526306270b 100644
--- a/backends/graphics/sdl/sdl-graphics.h
+++ b/backends/graphics/sdl/sdl-graphics.h
@@ -150,10 +150,7 @@ protected:
 #endif
 	}
 
-	virtual void setSystemMousePosition(const int x, const int y) override {
-		assert(_window);
-		_window->warpMouseInWindow(x, y);
-	}
+	virtual void setSystemMousePosition(const int x, const int y) override;
 
 	virtual void handleResizeImpl(const int width, const int height) override;
 
diff --git a/backends/modular-backend.cpp b/backends/modular-backend.cpp
index c9adbd3100..944ddd5a47 100644
--- a/backends/modular-backend.cpp
+++ b/backends/modular-backend.cpp
@@ -217,6 +217,7 @@ bool ModularBackend::showMouse(bool visible) {
 }
 
 void ModularBackend::warpMouse(int x, int y) {
+	_eventManager->purgeMouseEvents();
 	_graphicsManager->warpMouse(x, y);
 }
 
diff --git a/backends/platform/sdl/sdl-window.cpp b/backends/platform/sdl/sdl-window.cpp
index a550fbbd40..fe27d84de2 100644
--- a/backends/platform/sdl/sdl-window.cpp
+++ b/backends/platform/sdl/sdl-window.cpp
@@ -155,16 +155,20 @@ bool SdlWindow::hasMouseFocus() const {
 #endif
 }
 
-void SdlWindow::warpMouseInWindow(int x, int y) {
+bool SdlWindow::warpMouseInWindow(int x, int y) {
 	if (hasMouseFocus()) {
 #if SDL_VERSION_ATLEAST(2, 0, 0)
 		if (_window) {
 			SDL_WarpMouseInWindow(_window, x, y);
+			return true;
 		}
 #else
 		SDL_WarpMouse(x, y);
+		return true;
 #endif
 	}
+
+	return false;
 }
 
 void SdlWindow::iconifyWindow() {
diff --git a/backends/platform/sdl/sdl-window.h b/backends/platform/sdl/sdl-window.h
index 4f6d924411..e1a3499d19 100644
--- a/backends/platform/sdl/sdl-window.h
+++ b/backends/platform/sdl/sdl-window.h
@@ -58,8 +58,10 @@ public:
 	/**
 	 * Warp the mouse to the specified position in window coordinates. The mouse
 	 * will only be warped if the window is focused in the window manager.
+	 *
+	 * @returns true if the system cursor was warped.
 	 */
-	void warpMouseInWindow(int x, int y);
+	bool warpMouseInWindow(int x, int y);
 
 	/**
 	 * Iconifies the window.
diff --git a/common/events.h b/common/events.h
index 21a65a642b..e5bb8cab50 100644
--- a/common/events.h
+++ b/common/events.h
@@ -395,6 +395,11 @@ public:
 	 */
 	virtual void pushEvent(const Event &event) = 0;
 
+	/**
+	 * Purges all unprocessed mouse events already in the event queue.
+	 */
+	virtual void purgeMouseEvents() = 0;
+
 	/** Return the current mouse position */
 	virtual Point getMousePos() const = 0;