Grey out wxGrid row/column labels when it is disabled

Grid contents was drawn in grey colour instead of the usual active one
when it was disabled, but the row and column labels kept their default
appearance, which looked out of place.

Fix this by greying them out too. This should have been arguably done in
73145b0ed1 ~17 years ago, but better late
than never.

src/generic/grid.cpp

@@ -228,8 +228,35 @@ void wxGridHeaderLabelsRenderer::DrawLabel(const wxGrid& grid,
                                          int textOrientation) const
 {
     dc.SetBackgroundMode(wxBRUSHSTYLE_TRANSPARENT);
-    dc.SetTextForeground(grid.GetLabelTextColour());
     dc.SetFont(grid.GetLabelFont());
+
+    // Draw text in a different colour and with a shadow when the control
+    // is disabled.
+    //
+    // Note that the colours used here are consistent with wxGenericStaticText
+    // rather than our own wxGridCellStringRenderer::SetTextColoursAndFont()
+    // because this results in a better disabled appearance for the default
+    // bold font used for the labels.
+    wxColour colText;
+    if ( !grid.IsThisEnabled() )
+    {
+        colText = wxSystemSettings::GetColour(wxSYS_COLOUR_BTNHIGHLIGHT);
+        dc.SetTextForeground(colText);
+
+        wxRect rectShadow = rect;
+        rectShadow.Offset(1, 1);
+        grid.DrawTextRectangle(dc, value, rectShadow,
+                               horizAlign, vertAlign, textOrientation);
+
+        colText = wxSystemSettings::GetColour(wxSYS_COLOUR_BTNSHADOW);
+    }
+    else
+    {
+        colText = grid.GetLabelTextColour();
+    }
+
+    dc.SetTextForeground(colText);
+
     grid.DrawTextRectangle(dc, value, rect, horizAlign, vertAlign, textOrientation);
 }