Improve wxNotebook themed background drawing

Use GetThemeBackgroundContentRect() to properly draw the themed notebook
background in all configurations.

Closes #18156.

docs/changes.txt

@@ -130,6 +130,7 @@ wxMSW:
 - Support MSVC auto-linking when using monolithic build too (PB).
 - Implement wxFontDialog::SetTitle() (Vitaly Stakhovsky).
 - Fix build in ANSI (non-Unicode) mode.
+- Improve wxNotebook themed background drawing (Arrigo Marchiori).
 
 wxOSX:
 

include/wx/msw/notebook.h

@@ -170,10 +170,17 @@ protected:
   void AdjustPageSize(wxNotebookPage *page);
 
 #if wxUSE_UXTHEME
+  virtual void MSWAdjustBrushOrg(int *xOrg, int* yOrg) const wxOVERRIDE
+  {
+      *xOrg -= m_bgBrushAdj.x;
+      *yOrg -= m_bgBrushAdj.y;
+  }
+
   // return the themed brush for painting our children
   virtual WXHBRUSH MSWGetCustomBgBrush() wxOVERRIDE { return m_hbrBackground; }
 
-  // gets the bitmap of notebook background and returns a brush from it
+  // gets the bitmap of notebook background and returns a brush from it and
+  // sets m_bgBrushAdj
   WXHBRUSH QueryBgBitmap();
 
   // creates the brush to be used for drawing the tab control background
@@ -190,6 +197,9 @@ protected:
 #if wxUSE_UXTHEME
   // background brush used to paint the tab control
   WXHBRUSH m_hbrBackground;
+
+  // offset for MSWAdjustBrushOrg()
+  wxPoint m_bgBrushAdj;
 #endif // wxUSE_UXTHEME
 
 

src/msw/notebook.cpp

@@ -1095,30 +1095,40 @@ void wxNotebook::OnNavigationKey(wxNavigationKeyEvent& event)
 
 WXHBRUSH wxNotebook::QueryBgBitmap()
 {
-    wxRect r = GetPageSize();
-    if ( r.IsEmpty() )
+    RECT rc;
+    ::GetClientRect(GetHwnd(), &rc);
+    if ( ::IsRectEmpty(&rc) )
         return 0;
 
     wxUxThemeHandle theme(this, L"TAB");
     if ( !theme )
         return 0;
 
-    RECT rc;
-    wxCopyRectToRECT(r, rc);
-
     WindowHDC hDC(GetHwnd());
+
+    RECT rcBg;
+    ::GetThemeBackgroundContentRect(theme,
+                                    (HDC) hDC,
+                                    9, /* TABP_PANE */
+                                    0,
+                                    &rc,
+                                    &rcBg);
+
+    m_bgBrushAdj = wxPoint(rcBg.left, rcBg.top);
+    ::OffsetRect(&rcBg, -rcBg.left, -rcBg.top);
+
     ::GetThemeBackgroundExtent
                             (
                                 theme,
                                 (HDC) hDC,
                                 9 /* TABP_PANE */,
                                 0,
-                                &rc,
+                                &rcBg,
                                 &rc
                             );
 
     MemoryHDC hDCMem(hDC);
-    CompatibleBitmap hBmp(hDC, rc.right, rc.bottom);
+    CompatibleBitmap hBmp(hDC, rcBg.right, rcBg.bottom);
 
     {
         SelectInHDC selectBmp(hDCMem, hBmp);