In the previous section we learned how to use polar coordinates to place images at the vertices of a regular polygon. In this section we'll learn how to draw the polygon itself, using paths.

A path specifies how to control a virtual pen to draw a shape. There are three different commands that a path can contain:

Here's an example. First we create a path, which you may recognize as defining a hexagon using polar coordinates.

val hexagonPath =
    .moveTo(100, 0.degrees)
    .lineTo(100, 60.degrees)
    .lineTo(100, 120.degrees)
    .lineTo(100, 180.degrees)
    .lineTo(100, 240.degrees)
    .lineTo(100, 300.degrees)

Now we can create an Image from it.

val hexagonImage = Image.path(hexagonPath)

This produces the drawing below.

For more on paths, see the Doodle documentation.

Exercise: Paths to Polygons

Implement a method regularPolygon with skeleton

def regularPolygon(sides: Int, radius: Double): Image =

Given the number of sides and the radius is should produce a regular polygon using a ClosedPath.

The drawing below shows the output of

regularPolygon(3, 25)
  .on(regularPolygon(5, 50))
  .on(regularPolygon(7, 75))

The structure of this method is the same as polygonPoints: a structural recursion over the natural numbers, with an auxillary helper method. There is a little wrinkle where we convert the ClosedPath to an Image after calling the helper.

def regularPolygon(sides: Int, radius: Double): Image = {
  val turn = (1.0 / sides).turns
  def loop(count: Int): ClosedPath =
    count match {
      case 0 => ClosedPath.empty.moveTo(radius, 0.degrees)
      case n => loop(n - 1).lineTo(radius, turn * n)