Use custom draw in wxMSW wxHeaderCtrl to support colours

Add a helper wxMSWImpl::CustomDraw class which will be reused in the other
places too and, for now, use it just to implement support for custom colours
in wxHeaderCtrl.

Notice that the control took care of the custom font on its anyhow and that
background colour is ignored when themes are enabled, so the net effect of
this change is that now changing the header foreground colour works, while
it was ignored before.

src/msw/headerctrl.cpp

@@ -37,6 +37,7 @@
 
 #include "wx/msw/wrapcctl.h"
 #include "wx/msw/private.h"
+#include "wx/msw/private/customdraw.h"
 
 #ifndef HDM_SETBITMAPMARGIN
     #define HDM_SETBITMAPMARGIN 0x1234
@@ -50,6 +51,36 @@
 // from src/msw/listctrl.cpp
 extern int WXDLLIMPEXP_CORE wxMSWGetColumnClicked(NMHDR *nmhdr, POINT *ptClick);
 
+// ----------------------------------------------------------------------------
+// wxMSWHeaderCtrlCustomDraw: our custom draw helper
+// ----------------------------------------------------------------------------
+
+class wxMSWHeaderCtrlCustomDraw : public wxMSWImpl::CustomDraw
+{
+public:
+    wxMSWHeaderCtrlCustomDraw()
+    {
+    }
+
+    // Make this field public to let wxHeaderCtrl update it directly when its
+    // attributes change.
+    wxItemAttr m_attr;
+
+private:
+    virtual bool HasCustomDrawnItems() const wxOVERRIDE
+    {
+        // We only exist if the header does need to be custom drawn.
+        return true;
+    }
+
+    virtual const wxItemAttr*
+    GetItemAttr(DWORD_PTR WXUNUSED(dwItemSpec)) const wxOVERRIDE
+    {
+        // We use the same attribute for all items for now.
+        return &m_attr;
+    }
+};
+
 // ============================================================================
 // wxHeaderCtrl implementation
 // ============================================================================
@@ -64,6 +95,7 @@ void wxHeaderCtrl::Init()
     m_imageList = NULL;
     m_scrollOffset = 0;
     m_colBeingDragged = -1;
+    m_customDraw = NULL;
 }
 
 bool wxHeaderCtrl::Create(wxWindow *parent,
@@ -116,6 +148,7 @@ WXDWORD wxHeaderCtrl::MSWGetStyle(long style, WXDWORD *exstyle) const
 wxHeaderCtrl::~wxHeaderCtrl()
 {
     delete m_imageList;
+    delete m_customDraw;
 }
 
 // ----------------------------------------------------------------------------
@@ -466,6 +499,73 @@ int wxHeaderCtrl::MSWFromNativeOrder(int order)
     return pos;
 }
 
+// ----------------------------------------------------------------------------
+// wxHeaderCtrl appearance
+// ----------------------------------------------------------------------------
+
+wxMSWHeaderCtrlCustomDraw* wxHeaderCtrl::GetCustomDraw()
+{
+    // There is no need to make the control custom drawn just because it has a
+    // custom font, the native control handles the font just fine on its own,
+    // so if our custom colours were reset, don't bother with custom drawing
+    // any longer.
+    if ( !m_hasBgCol && !m_hasFgCol )
+    {
+        if ( m_customDraw )
+        {
+            delete m_customDraw;
+            m_customDraw = NULL;
+        }
+
+        return NULL;
+    }
+
+    // We do have at least one custom colour, so enable custom drawing.
+    if ( !m_customDraw )
+        m_customDraw = new wxMSWHeaderCtrlCustomDraw();
+
+    return m_customDraw;
+}
+
+bool wxHeaderCtrl::SetBackgroundColour(const wxColour& colour)
+{
+    if ( !wxHeaderCtrlBase::SetBackgroundColour(colour) )
+        return false;
+
+    if ( wxMSWHeaderCtrlCustomDraw* customDraw = GetCustomDraw() )
+    {
+        customDraw->m_attr.SetBackgroundColour(colour);
+    }
+
+    return true;
+}
+
+bool wxHeaderCtrl::SetForegroundColour(const wxColour& colour)
+{
+    if ( !wxHeaderCtrlBase::SetForegroundColour(colour) )
+        return false;
+
+    if ( wxMSWHeaderCtrlCustomDraw* customDraw = GetCustomDraw() )
+    {
+        customDraw->m_attr.SetTextColour(colour);
+    }
+
+    return true;
+}
+
+bool wxHeaderCtrl::SetFont(const wxFont& font)
+{
+    if ( !wxHeaderCtrlBase::SetFont(font) )
+        return false;
+
+    if ( wxMSWHeaderCtrlCustomDraw* customDraw = GetCustomDraw() )
+    {
+        customDraw->m_attr.SetFont(font);
+    }
+
+    return true;
+}
+
 // ----------------------------------------------------------------------------
 // wxHeaderCtrl events
 // ----------------------------------------------------------------------------
@@ -670,6 +770,18 @@ bool wxHeaderCtrl::MSWOnNotify(int idCtrl, WXLPARAM lParam, WXLPARAM *result)
             // Dragging the column was cancelled.
             m_colBeingDragged = -1;
             break;
+
+        // other events
+        // ------------
+
+        case NM_CUSTOMDRAW:
+            if ( m_customDraw )
+            {
+                *result = m_customDraw->HandleCustomDraw(lParam);
+                if ( *result != CDRF_DODEFAULT )
+                    return true;
+            }
+            break;
     }