[reactos] 01/01: [NTUSER] Handle window update region larger than the current window in clip region (#7731)

[Doug Lyons]

https://git.reactos.org/?p=reactos.git;a=commitdiff;h=5c505d9a9b804a5464f34…
commit 5c505d9a9b804a5464f348ebc09265f28d4b75b4
Author:     Doug Lyons <douglyons(a)douglyons.com>
AuthorDate: Sat Feb 22 23:31:50 2025 -0600
Commit:     Hermès Bélusca-Maïto <hermes.belusca-maito(a)reactos.org>
CommitDate: Wed Mar 12 12:18:53 2025 +0100
    [NTUSER] Handle window update region larger than the current window in clip region
(#7731)
    CORE-18206 CORE-18799 CORE-19371
    Fixes infinite loop of:
      err: Message WM_PAINT count 1 Internal Paint Set? FALSE
    The symptom appears in the following scenario (as reported in CORE-18799):
    A program (game) runs at a small resolution (e.g. 640 x 480), but the
    game window gets invalidated at a larger size (e.g. 1152 x 864 screen
    resolution) before switching to the smaller (640 x 480) size.
    Because of this, the window's update region is larger than the current
    window so only the 640 x 480 region gets validated leaving the remaining
    region invalid. This causes the recurring WM_PAINT messages because there
    is no way to invalidate the remaining area.
---
 win32ss/user/ntuser/winpos.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/win32ss/user/ntuser/winpos.c b/win32ss/user/ntuser/winpos.c
index d06730112be..da895726b7a 100644
--- a/win32ss/user/ntuser/winpos.c
+++ b/win32ss/user/ntuser/winpos.c
@@ -2037,7 +2037,17 @@ co_WinPosSetWindowPos(
       }
       else if(VisAfter)
       {
-         REGION_bOffsetRgn(VisAfter, -Window->rcWindow.left,
-Window->rcWindow.top);
+          /* Clip existing update region to new window size */
+          if (Window->hrgnUpdate != NULL)
+          {
+              PREGION RgnUpdate = REGION_LockRgn(Window->hrgnUpdate);
+              if (RgnUpdate)
+              {
+                  RgnType = IntGdiCombineRgn(RgnUpdate, RgnUpdate, VisAfter, RGN_AND);
+                  REGION_UnlockRgn(RgnUpdate);
+              }
+          }
+          REGION_bOffsetRgn(VisAfter, -Window->rcWindow.left,
-Window->rcWindow.top);
       }
       /*