simplify DrawingPanel classes w. dynamic_cast<>

Use dynamic_cast<wxWindow*>(this) in the DrawingPanel abstract class to
implement GetWindow() and Delete() so that all concrete classes do not
have to duplicate the code.

src/wx/drawing.h

@@ -6,14 +6,6 @@
 class BasicDrawingPanel : public DrawingPanel, public wxPanel {
 public:
     BasicDrawingPanel(wxWindow* parent, int _width, int _height);
-    wxWindow* GetWindow()
-    {
-        return this;
-    }
-    void Delete()
-    {
-        Destroy();
-    }
 
 protected:
     void PaintEv2(wxPaintEvent& ev)
@@ -33,14 +25,6 @@ class GLDrawingPanel : public DrawingPanel, public wxGLCanvas {
 public:
     GLDrawingPanel(wxWindow* parent, int _width, int _height);
     virtual ~GLDrawingPanel();
-    wxWindow* GetWindow()
-    {
-        return this;
-    }
-    void Delete()
-    {
-        Destroy();
-    }
 
 protected:
     void PaintEv2(wxPaintEvent& ev)
@@ -64,14 +48,6 @@ protected:
 class DXDrawingPanel : public DrawingPanel, public wxPanel {
 public:
     DXDrawingPanel(wxWindow* parent, int _width, int _height);
-    wxWindow* GetWindow()
-    {
-        return this;
-    }
-    void Delete()
-    {
-        Destroy();
-    }
 
 protected:
     void PaintEv2(wxPaintEvent& ev)
@@ -93,14 +69,6 @@ class CairoDrawingPanel : public DrawingPanel, public wxPanel {
 public:
     CairoDrawingPanel(wxWindow* parent, int _width, int _height);
     ~CairoDrawingPanel();
-    wxWindow* GetWindow()
-    {
-        return this;
-    }
-    void Delete()
-    {
-        Destroy();
-    }
 
 protected:
     void PaintEv2(wxPaintEvent& ev)

src/wx/wxvbam.h

@@ -628,9 +628,11 @@ public:
     DrawingPanel(int _width, int _height);
     ~DrawingPanel();
     void DrawArea(uint8_t** pixels);
-    // the following wouldn't be necessary with virtual inheritance
+
-    virtual wxWindow* GetWindow() = 0;
+    // using dynamic_cast<> to not force trivial reimplementation in concrete classes
-    virtual void Delete() = 0;
+    // TODO: figure something out for PaintEv as well
+    virtual wxWindow* GetWindow() { return dynamic_cast<wxWindow*>(this); }
+    virtual void Delete() { (dynamic_cast<wxWindow*>(this))->Destroy(); }
 
 protected:
     virtual void DrawArea(wxWindowDC&) = 0;