user32: Erase parent window when child is hidden. From a patch by Clinton Stimpson.

dlls/user32/painting.c

@@ -280,7 +280,7 @@ static BOOL send_erase( HWND hwnd, UINT flags, HRGN client_rgn,
  *
  * Implementation of RDW_ERASENOW behavior.
  */
-static void erase_now( HWND hwnd, UINT rdw_flags )
+void erase_now( HWND hwnd, UINT rdw_flags )
 {
     HWND child = 0;
     HRGN hrgn;

dlls/user32/tests/msg.c

@@ -3994,7 +3994,7 @@ static void test_messages(void)
     /* check parent messages too */
     log_all_parent_messages++;
     ShowWindow(hchild, SW_HIDE);
-    ok_sequence(WmHideChildSeq2, "ShowWindow(SW_HIDE):child", TRUE);
+    ok_sequence(WmHideChildSeq2, "ShowWindow(SW_HIDE):child", FALSE);
     log_all_parent_messages--;
 
     ShowWindow(hchild, SW_SHOW);

dlls/user32/user_private.h

@@ -213,6 +213,7 @@ extern HBRUSH SYSCOLOR_55AABrush;
 extern BOOL CLIPBOARD_ReleaseOwner(void);
 extern BOOL FOCUS_MouseActivate( HWND hwnd );
 extern BOOL HOOK_IsHooked( INT id );
+extern void erase_now( HWND hwnd, UINT rdw_flags );
 extern LRESULT call_current_hook( HHOOK hhook, INT code, WPARAM wparam, LPARAM lparam );
 extern LRESULT MSG_SendInternalMessageTimeout( DWORD dest_pid, DWORD dest_tid,
                                                UINT msg, WPARAM wparam, LPARAM lparam,

dlls/user32/winpos.c

@@ -1604,13 +1604,19 @@ BOOL USER_SetWindowPos( WINDOWPOS * winpos )
                             &newWindowRect, &newClientRect, orig_flags, valid_rects ))
         return FALSE;
 
-    /* Windows doesn't redraw a window if it is being just moved */
-    if (!(orig_flags & SWP_SHOWWINDOW) &&
+    /* erase parent if hiding child */
+    if (!(orig_flags & SWP_DEFERERASE))
+    {
+        if (orig_flags & SWP_HIDEWINDOW)
+        {
+            HWND parent = GetAncestor( winpos->hwnd, GA_PARENT );
+            erase_now( parent, RDW_NOCHILDREN );
+        }
+        else if (!(orig_flags & SWP_SHOWWINDOW) &&
                  (winpos->flags & SWP_AGG_STATUSFLAGS) != SWP_AGG_NOGEOMETRYCHANGE)
         {
-        UINT rdw_flags = RDW_FRAME | RDW_ERASE;
-        if ( !(orig_flags & SWP_DEFERERASE) ) rdw_flags |= RDW_ERASENOW;
-        RedrawWindow( winpos->hwnd, NULL, NULL, rdw_flags );
+            erase_now( winpos->hwnd, 0 );
+        }
     }
 
     if( winpos->flags & SWP_HIDEWINDOW )