// Use the non-transparent pixels of a wxBitmap for the region to combine
// with this region. If the bitmap has a mask then it will be used,
// otherwise the colour to be treated as transparent may be specified,
// Use the non-transparent pixels of a wxBitmap for the region to combine
// with this region. If the bitmap has a mask then it will be used,
// otherwise the colour to be treated as transparent may be specified,