Mask

class Sprite
  def mask(mask=nil)
    return false if !self.bitmap
    bitmap=self.bitmap.clone
    if mask.is_a?(Bitmap)
      mbmp=mask
    elsif mask.is_a?(Sprite)
      mbmp=mask.bitmap
    elsif mask.is_a?(String)
      mbmp=BitmapCache.load_bitmap(mask)
    else
      return false
    end

    self.bitmap=Bitmap.new(bitmap.width,bitmap.height)
    mask=Bitmap.new(bitmap.width,bitmap.height)
    mask.stretch_blt(Rect.new(0,0,mask.width,mask.height),mbmp,Rect.new(0,0,mbmp.width,mbmp.height))

    for y in 0...bitmap.height
      for x in 0...bitmap.width
        pixel=mask.get_pixel(x,y)
        color=bitmap.get_pixel(x,y)
        alpha=pixel.alpha
        alpha=color.alpha if color.alpha<pixel.alpha
        self.bitmap.set_pixel(x,y,Color.new(color.red,color.green,color.blue,alpha))
      end
    end
  end
end