[Git][wxwidgets/wxwidgets][master] Fix wxPaintDC invalidation in wxMSW wxNotebook in dark mode

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Vadim Zeitlin (@_VZ_)

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Aug 17, 2025, 7:12:30 PMAug 17

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Vadim Zeitlin pushed to branch master at wxWidgets / wxWidgets

Commits:

365b07b7

by Vadim Zeitlin at 2025-08-18T00:45:32+02:00

Fix wxPaintDC invalidation in wxMSW wxNotebook in dark mode

Claling GetTabRect() while painting wxNotebook could result in another
WM_PAINT sent by the native control when using multiple tab rows and
after handling this nested WM_PAINT wxMSW code called EndPaint() on the
DC used by wxPaintDC that we had created before calling GetTabRect().

This is almost certainly wrong and we should use reference counting
instead of assuming that nothing can use the HDC once we return from
WM_PAINT handler as the code seems to be doing currently, but for now
just avoid the problem by calling GetTabRect() before creating wxPaintDC
instead to ensure that wxPaintDC remains valid while we draw on it.

Closes #25700.

Changes:

include/wx/msw/notebook.h


   void OnEraseBackground(wxEraseEvent& event);
   void OnPaint(wxPaintEvent& event);
 
-  // Paint the notebook ourselves on the provided DC.
-  void MSWNotebookPaint(wxDC& dc);
+  // Paint the notebook ourselves using wxPaintDC (so this can be only called
+  // from wxEVT_PAINT handler).
+  void MSWNotebookPaint();
 
 
   // true if we have already subclassed our updown control

src/msw/notebook.cpp


 
 } // anonymous namespace
 
-void wxNotebook::MSWNotebookPaint(wxDC& dc)
+void wxNotebook::MSWNotebookPaint()
 {
+    // This is tricky: GetTabRect() may result in a nested WM_PAINT when the
+    // native control decides to generate it from its Tab_CalcPaintMetrics()
+    // for some reason (this happens at least when using multiple tab rows), so
+    // we need to call it before creating wxPaintDC as otherwise the current
+    // paint DC would be invalidated by EndPaint() while we use it, see #25700.
+    wxRect rectTabArea = GetTabRect(0);
+
+    // Now create and use the DC.
+    wxPaintDC dc(this);
     dc.Clear();
 
     const wxDirection tabOrient = GetTabOrientation();

         return;
 
     // Start by erasing the tabs area background.
-    wxRect rectTabArea = GetTabRect(0);
     rectTabArea = ExpandSelectedTab(rectTabArea, tabOrient);
     if ( tabOrient == wxTOP || tabOrient == wxBOTTOM )
         rectTabArea.SetRight(sizeWindow.x);

         return;
     }
 
-    wxPaintDC dc(this);
-
     if ( wxMSWDarkMode::IsActive() )
     {
         // We can't use default painting in dark mode, it just doesn't work
         // there, whichever theme we use, so draw everything ourselves.
-        MSWNotebookPaint(dc);
+        MSWNotebookPaint();
         return;
     }
 
+    wxPaintDC dc(this);
+
     RECT rc;
     ::GetClientRect(GetHwnd(), &rc);
     if ( !rc.right || !rc.bottom )

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...	...	@@ -183,8 +183,9 @@ protected:
183	183	void OnEraseBackground(wxEraseEvent& event);
184	184	void OnPaint(wxPaintEvent& event);
185	185
186		- // Paint the notebook ourselves on the provided DC.
187		- void MSWNotebookPaint(wxDC& dc);
	186	+ // Paint the notebook ourselves using wxPaintDC (so this can be only called
	187	+ // from wxEVT_PAINT handler).
	188	+ void MSWNotebookPaint();
188	189
189	190
190	191	// true if we have already subclassed our updown control

...	...	@@ -1255,8 +1255,17 @@ DrawNotebookTab(wxWindow* win,
1255	1255
1256	1256	} // anonymous namespace
1257	1257
1258		-void wxNotebook::MSWNotebookPaint(wxDC& dc)
	1258	+void wxNotebook::MSWNotebookPaint()
1259	1259	{
	1260	+ // This is tricky: GetTabRect() may result in a nested WM_PAINT when the
	1261	+ // native control decides to generate it from its Tab_CalcPaintMetrics()
	1262	+ // for some reason (this happens at least when using multiple tab rows), so
	1263	+ // we need to call it before creating wxPaintDC as otherwise the current
	1264	+ // paint DC would be invalidated by EndPaint() while we use it, see #25700.
	1265	+ wxRect rectTabArea = GetTabRect(0);
	1266	+
	1267	+ // Now create and use the DC.
	1268	+ wxPaintDC dc(this);
1260	1269	dc.Clear();
1261	1270
1262	1271	const wxDirection tabOrient = GetTabOrientation();
...	...	@@ -1282,7 +1291,6 @@ void wxNotebook::MSWNotebookPaint(wxDC& dc)
1282	1291	return;
1283	1292
1284	1293	// Start by erasing the tabs area background.
1285		- wxRect rectTabArea = GetTabRect(0);
1286	1294	rectTabArea = ExpandSelectedTab(rectTabArea, tabOrient);
1287	1295	if ( tabOrient == wxTOP \|\| tabOrient == wxBOTTOM )
1288	1296	rectTabArea.SetRight(sizeWindow.x);
...	...	@@ -1370,16 +1378,16 @@ void wxNotebook::OnPaint(wxPaintEvent& event)
1370	1378	return;
1371	1379	}
1372	1380
1373		- wxPaintDC dc(this);
1374		-
1375	1381	if ( wxMSWDarkMode::IsActive() )
1376	1382	{
1377	1383	// We can't use default painting in dark mode, it just doesn't work
1378	1384	// there, whichever theme we use, so draw everything ourselves.
1379		- MSWNotebookPaint(dc);
	1385	+ MSWNotebookPaint();
1380	1386	return;
1381	1387	}
1382	1388
	1389	+ wxPaintDC dc(this);
	1390	+
1383	1391	RECT rc;
1384	1392	::GetClientRect(GetHwnd(), &rc);
1385	1393	if ( !rc.right \|\| !rc.bottom )