fix repaining of highlight for merged cells [backport of r55630 from trunk] (closes #9718)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@58753 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -132,6 +132,7 @@ All (GUI):
   wxMac with CoreGraphics where sash drawing isn't implemented.
 - Use bitmap mask in wxSplashScreen.
 - Translate "(c)" and "(C)" to the real copyright sign in wxAboutBox.
+- Fix painting of highlight border for merged cells in wxGrid (K. Jones).
 
 All (Unix):
 

src/generic/grid.cpp

@@ -7859,7 +7859,27 @@ void wxGrid::DrawHighlight(wxDC& dc, const wxGridCellCoordsArray& cells)
     size_t count = cells.GetCount();
     for ( size_t n = 0; n < count; n++ )
     {
-        if ( cells[n] == m_currentCellCoords )
+        wxGridCellCoords cell = cells[n];
+
+        // If we are using attributes, then we may have just exposed another
+        // cell in a partially-visible merged cluster of cells. If the "anchor"
+        // (upper left) cell of this merged cluster is the cell indicated by
+        // m_currentCellCoords, then we need to refresh the cell highlight even
+        // though the "anchor" itself is not part of our update segment.
+        if ( CanHaveAttributes() )
+        {
+            int rows = 0,
+                cols = 0;
+            GetCellSize(cell.GetRow(), cell.GetCol(), &rows, &cols);
+
+            if ( rows < 0 )
+                cell.SetRow(cell.GetRow() + rows);
+
+            if ( cols < 0 )
+                cell.SetCol(cell.GetCol() + cols);
+        }
+
+        if ( cell == m_currentCellCoords )
         {
             wxGridCellAttr* attr = GetCellAttr(m_currentCellCoords);
             DrawCellHighlight(dc, attr);