class Circle
  self.get_circle(x_center, y_center, r, color, bitmap)
    x = 0
    y = r
    d = r - 1
    while(y >= x)
      bitmap.set_pixel(x, y, color)
      if(d >= 2 * x)
        d = d - 2 * x - 1
        x+=1
      elsif(d <= (2 * r - y))
        d = d + 2 * y - 1
        y-=1
      else
        d + 2 * (y - x - 1)
        y = y -1
        x +=1
      end
    end
    return bitmap
  end
end