CrSFML: Rounded polygon shape

rounded_polygon_shape.cr

class RoundedPolygon < SF::Shape
  def initialize
    super()

    @result = [] of SF::Vector2f
  end

  def assign(points, radius : Number)
    @result.clear

    unless points.size < 2
      p1 = points[points.size - 1]
      a1 = p1 - points[points.size - 2]
      a1 = Math.atan2(-a1.x, a1.y)

      points.each do |p2|
        a2 = p2 - p1
        a2 = Math.atan2(-a2.x, a2.y)  # normal angle

        a2 += Math::PI * 2 if a2 < a1
        steps = (radius == 0 ? 1 : ((a2 - a1) * 3).round.to_i)
        (0..steps).each do |i|
          a = a2 * i / steps + a1 * (steps - i) / steps
          @result << SF.vector2f(p1.x + Math.cos(a)*radius, p1.y + Math.sin(a)*radius)
        end

        a1 = a2
        p1 = p2
      end
    end

    update()
  end

  def point_count
    @result.size
  end
  def get_point(index)
    @result[index]
  end
end