[PATCH v3 6/8] win32u: GetUpdateRect() should clip update rectangle to the window client area.

[Dmitry Timoshkov]

From: Dmitry Timoshkov

Signed-off-by: Dmitry Timoshkov 
---
 dlls/win32u/dce.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/dlls/win32u/dce.c b/dlls/win32u/dce.c
index 76570b2747b..fa8f61301be 100644
--- a/dlls/win32u/dce.c
+++ b/dlls/win32u/dce.c
@@ -1471,13 +1471,20 @@ INT WINAPI NtUserGetUpdateRgn( HWND hwnd, HRGN hrgn, BOOL erase )
 BOOL WINAPI NtUserGetUpdateRect( HWND hwnd, RECT *rect, BOOL erase )
 {
     UINT flags = UPDATE_NOCHILDREN;
-    HRGN update_rgn;
+    HRGN update_rgn, client_rgn;
+    RECT client_rect;
     BOOL need_erase;

if (erase) flags |= UPDATE_NONCLIENT | UPDATE_ERASE;

if (!(update_rgn = send_ncpaint( hwnd, NULL, &flags ))) return FALSE;

+    get_window_rects( hwnd, COORDS_SCREEN, NULL, &client_rect, get_thread_dpi() );
+
+    client_rgn = NtGdiCreateRectRgn( client_rect.left, client_rect.top, client_rect.right, client_rect.bottom );
+    NtGdiCombineRgn( update_rgn, update_rgn, client_rgn, RGN_AND );
+    NtGdiDeleteObjectApp( client_rgn );
+
     if (rect && NtGdiGetRgnBox( update_rgn, rect ) != NULLREGION)
     {
         HDC hdc = NtUserGetDCEx( hwnd, 0, DCX_USESTYLE );