Date: Sat, 06 Dec 2008 15:27:00 +0100

From: Couriersud
Subject: SDL: Relative mouse movements

The patch below will reenable processing of relative mouse movements.
The DirectFB drivers generates those in "grabbed" mode. These ensure,
that even in fullscreen mode relative movements are reported. SDLMAME
depends on this for games with trackballs.

Looking at the code I ask myself whether relative movements should be
handled in the drivers (x11, directfb). Both x11 and directfb are able
to report relative movements. This would leave it to the driver to use
the most appropriate method for relative movements when at the border of
a fullscreen window or being "grabbed".

src/events/SDL_mouse.c

@@ -433,9 +433,15 @@ SDL_SendMouseMotion(int id, int relative, int x, int y, int pressure)
     }
 
     /* the relative motion is calculated regarding the system cursor last position */
-
-    xrel = x - last_x;
-    yrel = y - last_y;
+    if (relative) {
+        xrel = x;
+        yrel = y;
+        x = (last_x + x);
+        y = (last_y + y);
+    } else {
+        xrel = x - last_x;
+        yrel = y - last_y;
+    }
 
     /* Drop events that don't change state */
     if (!xrel && !yrel) {