vivid_png/lib/vivid/png/shape.ex

defmodule Vivid.PNG.ShapeToPng do
  alias Vivid.{Bounds, Frame, PNG, RGBA, Shape, Transform}

  @moduledoc false

  @doc false
  @spec to_png(Shape.t(), Path.t()) :: :ok | {:error, any}
  def to_png(shape, file) do
    bounds = Bounds.bounds(shape)
    width = bounds |> Bounds.width() |> round |> Kernel.+(3)
    height = bounds |> Bounds.height() |> round |> Kernel.+(3)

    frame = Frame.init(width, height)

    shape =
      shape
      |> Transform.center(frame)
      |> Transform.apply()

    frame
    |> Frame.push(shape, RGBA.black())
    |> PNG.to_png(file)
  end
end

Enum.each(~w(Arc Box Circle Group Line Path Polygon), fn mod ->
  mod = Module.concat(Vivid, mod)

  defimpl Vivid.PNG, for: mod do
    def to_png(shape, file), do: Vivid.PNG.ShapeToPng.to_png(shape, file)
  end
end)