(svn r27167) -Fix: [SDL, Windows] Right-mouse-button scrolling scrolled/jumped way to far, when OpenTTD lagged during mouse event processing.

src/gfx.cpp

@@ -1603,6 +1603,53 @@ void SetAnimatedMouseCursor(const AnimCursor *table)
 	SwitchAnimatedCursor();
 }
 
+/**
+ * Update cursor position on mouse movement.
+ * @param x New X position.
+ * @param y New Y position.
+ * @param queued True, if the OS queues mouse warps after pending mouse movement events.
+ *               False, if the warp applies instantaneous.
+ * @return true, if the OS cursor position should be warped back to this->pos.
+ */
+bool CursorVars::UpdateCursorPosition(int x, int y, bool queued_warp)
+{
+	/* Detecting relative mouse movement is somewhat tricky.
+	 *  - There may be multiple mouse move events in the video driver queue (esp. when OpenTTD lags a bit).
+	 *  - When we request warping the mouse position (return true), a mouse move event is appended at the end of the queue.
+	 *
+	 * So, when this->fix_at is active, we use the following strategy:
+	 *  - The first movement triggers the warp to reset the mouse position.
+	 *  - Subsequent events have to compute movement relative to the previous event.
+	 *  - The relative movement is finished, when we receive the event matching the warp.
+	 */
+
+	if (x == this->pos.x && y == this->pos.y) {
+		/* Warp finished. */
+		this->queued_warp = false;
+	}
+
+	this->delta.x = x - (this->queued_warp ? this->last_position.x : this->pos.x);
+	this->delta.y = y - (this->queued_warp ? this->last_position.y : this->pos.y);
+
+	this->last_position.x = x;
+	this->last_position.y = y;
+
+	bool need_warp = false;
+	if (this->fix_at) {
+		if (!this->queued_warp && (this->delta.x != 0 || this->delta.y != 0)) {
+			/* Trigger warp. */
+			this->queued_warp = queued_warp;
+			need_warp = true;
+		}
+	} else if (this->pos.x != x || this->pos.y != y) {
+		this->queued_warp = false; // Cancel warping, we are no longer confining the position.
+		this->dirty = true;
+		this->pos.x = x;
+		this->pos.y = y;
+	}
+	return need_warp;
+}
+
 bool ChangeResInGame(int width, int height)
 {
 	return (_screen.width == width && _screen.height == height) || VideoDriver::GetInstance()->ChangeResolution(width, height);

src/gfx_type.h

@@ -138,6 +138,12 @@ struct CursorVars {
 	bool in_window;  ///< mouse inside this window, determines drawing logic
 
 	bool vehchain;   ///< vehicle chain is dragged
+
+	bool UpdateCursorPosition(int x, int y, bool queued_warp);
+
+private:
+	bool queued_warp;
+	Point last_position;
 };
 
 /** Data about how and where to blit pixels. */

src/video/allegro_v.cpp

@@ -388,22 +388,10 @@ static void PollEvent()
 	}
 
 	/* Mouse movement */
-	int dx = mouse_x - _cursor.pos.x;
-	int dy = mouse_y - _cursor.pos.y;
-	if (dx != 0 || dy != 0) {
-		if (_cursor.fix_at) {
-			_cursor.delta.x = dx;
-			_cursor.delta.y = dy;
-			position_mouse(_cursor.pos.x, _cursor.pos.y);
-		} else {
-			_cursor.delta.x = dx;
-			_cursor.delta.y = dy;
-			_cursor.pos.x = mouse_x;
-			_cursor.pos.y = mouse_y;
-			_cursor.dirty = true;
-		}
-		mouse_action = true;
+	if (_cursor.UpdateCursorPosition(mouse_x, mouse_y, false)) {
+		position_mouse(_cursor.pos.x, _cursor.pos.y);
 	}
+	if (_cursor.delta.x != 0 || _cursor.delta.y) mouse_action = true;
 
 	static int prev_mouse_z = 0;
 	if (prev_mouse_z != mouse_z) {

src/video/cocoa/event.mm

@@ -362,22 +362,8 @@ static void QZ_DoUnsidedModifiers(unsigned int newMods)
 
 static void QZ_MouseMovedEvent(int x, int y)
 {
-	if (_cursor.fix_at) {
-		int dx = x - _cursor.pos.x;
-		int dy = y - _cursor.pos.y;
-
-		if (dx != 0 || dy != 0) {
-			_cursor.delta.x += dx;
-			_cursor.delta.y += dy;
-
-			QZ_WarpCursor(_cursor.pos.x, _cursor.pos.y);
-		}
-	} else {
-		_cursor.delta.x = x - _cursor.pos.x;
-		_cursor.delta.y = y - _cursor.pos.y;
-		_cursor.pos.x = x;
-		_cursor.pos.y = y;
-		_cursor.dirty = true;
+	if (_cursor.UpdateCursorPosition(x, y, false)) {
+		QZ_WarpCursor(_cursor.pos.x, _cursor.pos.y);
 	}
 	HandleMouseEvents();
 }

src/video/sdl_v.cpp

@@ -545,20 +545,8 @@ int VideoDriver_SDL::PollEvent()
 
 	switch (ev.type) {
 		case SDL_MOUSEMOTION:
-			if (_cursor.fix_at) {
-				int dx = ev.motion.x - _cursor.pos.x;
-				int dy = ev.motion.y - _cursor.pos.y;
-				if (dx != 0 || dy != 0) {
-					_cursor.delta.x = dx;
-					_cursor.delta.y = dy;
-					SDL_CALL SDL_WarpMouse(_cursor.pos.x, _cursor.pos.y);
-				}
-			} else {
-				_cursor.delta.x = ev.motion.x - _cursor.pos.x;
-				_cursor.delta.y = ev.motion.y - _cursor.pos.y;
-				_cursor.pos.x = ev.motion.x;
-				_cursor.pos.y = ev.motion.y;
-				_cursor.dirty = true;
+			if (_cursor.UpdateCursorPosition(ev.motion.x, ev.motion.y, true)) {
+				SDL_CALL SDL_WarpMouse(_cursor.pos.x, _cursor.pos.y);
 			}
 			HandleMouseEvents();
 			break;

src/video/win32_v.cpp

@@ -747,25 +747,11 @@ static LRESULT CALLBACK WndProcGdi(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lP
 				SetTimer(hwnd, TID_POLLMOUSE, MOUSE_POLL_DELAY, (TIMERPROC)TrackMouseTimerProc);
 			}
 
-			if (_cursor.fix_at) {
-				int dx = x - _cursor.pos.x;
-				int dy = y - _cursor.pos.y;
-				if (dx != 0 || dy != 0) {
-					_cursor.delta.x = dx;
-					_cursor.delta.y = dy;
-
-					pt.x = _cursor.pos.x;
-					pt.y = _cursor.pos.y;
-
-					ClientToScreen(hwnd, &pt);
-					SetCursorPos(pt.x, pt.y);
-				}
-			} else {
-				_cursor.delta.x = x - _cursor.pos.x;
-				_cursor.delta.y = y - _cursor.pos.y;
-				_cursor.pos.x = x;
-				_cursor.pos.y = y;
-				_cursor.dirty = true;
+			if (_cursor.UpdateCursorPosition(x, y, true)) {
+				pt.x = _cursor.pos.x;
+				pt.y = _cursor.pos.y;
+				ClientToScreen(hwnd, &pt);
+				SetCursorPos(pt.x, pt.y);
 			}
 			MyShowCursor(false);
 			HandleMouseEvents();