user32: Scroll window fix.

dlls/user32/painting.c

@@ -870,6 +870,25 @@ INT WINAPI ScrollWindowEx( HWND hwnd, INT dx, INT dy,
                 CombineRgn( hrgnWinupd, hrgnWinupd, hrgnTemp, RGN_OR );
             RedrawWindow( hwnd, NULL, hrgnTemp, rdw_flags);
             DeleteObject( hrgnClip );
+
+           /* Catch the case where the scolling amount exceeds the size of the
+            * original window. This generated a second update area that is the
+            * location where the original scrolled content would end up.
+            * This second region is not returned by the ScrollDC and sets
+            * ScrollWindowEx apart from just a ScrollDC.
+            *
+            * This has been verified with testing on windows.
+            */
+            if (abs(dx) > abs(rc.right - rc.left) ||
+                abs(dy) > abs(rc.bottom - rc.top))
+            {
+                SetRectRgn( hrgnTemp, rc.left + dx, rc.top + dy, rc.right+dx, rc.bottom + dy);
+                CombineRgn( hrgnTemp, hrgnTemp, hrgnClip, RGN_AND );
+                CombineRgn( hrgnUpdate, hrgnUpdate, hrgnTemp, RGN_OR );
+
+                if( !bOwnRgn)
+                    CombineRgn( hrgnWinupd, hrgnWinupd, hrgnTemp, RGN_OR );
+            }
         }
         DeleteObject( hrgnTemp );
     } else {

dlls/user32/tests/win.c

@@ -2991,6 +2991,15 @@ static void test_scrollvalidate( HWND parent)
     CombineRgn( exprgn, exprgn, tmprgn, RGN_OR);
     ok( EqualRgn( exprgn, hrgn), "wrong update region\n");
 
+    SetRect( &rc, 0,40, 100,60);
+    SetRect( &cliprc, 0,0, 100,100);
+    ScrollWindowEx( hwnd1, 0, -25, &rc, &cliprc, hrgn, &rcu, SW_INVALIDATE);
+    SetRectRgn( tmprgn, 0,15,98,35);
+    CombineRgn( exprgn, exprgn, tmprgn, RGN_OR);
+    SetRectRgn( tmprgn, 0, 40, 98, 60);
+    CombineRgn( exprgn, exprgn, tmprgn, RGN_OR);
+    ok( EqualRgn( exprgn, hrgn), "wrong update region in excessive scroll\n");
+
     /* now test ScrollWindowEx with a combination of
      * WS_CLIPCHILDREN style and SW_SCROLLCHILDREN flag */
     /* make hwnd2 the child of hwnd1 */