Implemented SDL_GetAbsoluteMouseState().

X11 only for now, but this should be doable on every platform, I think.

src/events/SDL_mouse.c

@@ -469,6 +469,30 @@ SDL_GetRelativeMouseState(int *x, int *y)
     return mouse->buttonstate;
 }
 
+Uint32
+SDL_GetAbsoluteMouseState(int *x, int *y)
+{
+    SDL_Mouse *mouse = SDL_GetMouse();
+    int tmpx, tmpy;
+
+    /* make sure these are never NULL for the backend implementations... */
+    if (!x) {
+        x = &tmpx;
+    }
+    if (!y) {
+        y = &tmpy;
+    }
+
+    *x = *y = 0;
+
+    if (!mouse->GetAbsoluteMouseState) {
+        SDL_assert(0 && "This should really be implemented for every target.");
+        return 0;
+    }
+
+    return mouse->GetAbsoluteMouseState(x, y);
+}
+
 void
 SDL_WarpMouseInWindow(SDL_Window * window, int x, int y)
 {

src/events/SDL_mouse_c.h

@@ -66,6 +66,9 @@ typedef struct
     /* Set mouse capture */
     int (*CaptureMouse) (SDL_Window * window);
 
+    /* Get absolute mouse coordinates. (x) and (y) are never NULL and set to zero before call. */
+    Uint32 (*GetAbsoluteMouseState) (int *x, int *y);
+
     /* Data common to all mice */
     SDL_MouseID mouseID;
     SDL_Window *focus;