added alpha channel support to wxGTK2's wxBitmap

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@28850 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk1/dcclient.cpp

@@ -1147,7 +1147,21 @@ void wxWindowDC::DoDrawBitmap( const wxBitmap &bitmap,
     }
     else
     {
-        gdk_draw_pixmap( m_window, m_penGC, use_bitmap.GetPixmap(), 0, 0, xx, yy, -1, -1 );
+#if GTK_CHECK_VERSION(2,2,0)
+        if (use_bitmap.HasPixbuf())
+        {
+            gdk_draw_pixbuf(m_window, m_penGC,
+                            use_bitmap.GetPixbuf(),
+                            0, 0, xx, yy, -1, -1,
+                            GDK_RGB_DITHER_NORMAL, xx, yy);
+        }
+        else
+#endif
+        {
+            gdk_draw_pixmap(m_window, m_penGC,
+                            use_bitmap.GetPixmap(),
+                            0, 0, xx, yy, -1, -1);
+        }
     }
 
     // remove mask again if any