# HG changeset patch
# User peter1138 <peter1138@openttd.org>
# Date 1257630101 0
# Node ID 122917aef385c0186d081f11e77610ad5a1ae5b3
# Parent  7e6ed48b91625412206a9c3c3951c4df828d643b
(svn r18001) -Codechange: [SDL] When the mouse cursor is locked into position when scrolling a viewport, warp the mouse pointer to the centre of the window. This gives maximum freedom of movement. The pointer position is restored when the lock is removed. Visually the mouse cursor stays where it was.

diff --git a/src/video/sdl_v.cpp b/src/video/sdl_v.cpp
--- a/src/video/sdl_v.cpp
+++ b/src/video/sdl_v.cpp
@@ -29,6 +29,8 @@
 
 static SDL_Surface *_sdl_screen;
 static bool _all_modes;
+/** Flag used to determine if _cursor.fix_at has changed. */
+static bool _last_fix_at;
 
 /** Whether the drawing is/may be done in a separate thread. */
 static bool _draw_threaded;
@@ -363,17 +365,29 @@
 {
 	SDL_Event ev;
 
+	if (_cursor.fix_at != _last_fix_at) {
+		_last_fix_at = _cursor.fix_at;
+		if (_last_fix_at) {
+			/* Move to centre of window */
+			SDL_CALL SDL_WarpMouse(_screen.width / 2, _screen.height / 2);
+
+		} else {
+			/* Restore position */
+			SDL_CALL SDL_WarpMouse(_cursor.pos.x, _cursor.pos.y);
+		}
+	}
+
 	if (!SDL_CALL SDL_PollEvent(&ev)) return -2;
 
 	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;
+				int dx = ev.motion.x - _screen.width / 2;
+				int dy = ev.motion.y - _screen.height / 2;
 				if (dx != 0 || dy != 0) {
 					_cursor.delta.x += dx;
 					_cursor.delta.y += dy;
-					SDL_CALL SDL_WarpMouse(_cursor.pos.x, _cursor.pos.y);
+					SDL_CALL SDL_WarpMouse(_screen.width / 2, _screen.height / 2);
 				}
 			} else {
 				_cursor.delta.x = ev.motion.x - _cursor.pos.x;