Add wxDataViewCtrl debug option to display render bounds

For debugging convenience define DEBUG_RENDER_EXTENTS to draw a red
rectangle around a custom rendered cell's full rectangle, and a green
rect for the extent of the item appearing inside it. Custom renderers
ordinarily should not draw outside of the green rect. A notable
exception is drawn text, particularly multi-line ones.

src/common/datavcmn.cpp

@@ -32,6 +32,10 @@
     #include "wx/access.h"
 #endif // wxUSE_ACCESSIBILITY
 
+// Uncomment this line to, for custom renderers, visually show the extent
+// of both a cell and its item.
+//#define DEBUG_RENDER_EXTENTS
+
 const char wxDataViewCtrlNameStr[] = "dataviewCtrl";
 
 namespace
@@ -1035,6 +1039,20 @@ wxDataViewCustomRendererBase::WXCallRender(wxRect rectCell, wxDC *dc, int state)
     if ( m_attr.HasFont() )
         changeFont.Set(m_attr.GetEffectiveFont(dc->GetFont()));
 
+#ifdef DEBUG_RENDER_EXTENTS
+    {
+
+    wxDCBrushChanger changeBrush(*dc, *wxTRANSPARENT_BRUSH);
+    wxDCPenChanger changePen(*dc, *wxRED);
+
+    dc->DrawRectangle(rectCell);
+
+    dc->SetPen(*wxGREEN);
+    dc->DrawRectangle(rectItem);
+
+    }
+#endif
+
     Render(rectItem, dc, state);
 }