func poly(t *terrapin.Terrapin, size float64, sides int) {
totalInterior := math.Pi * float64(sides-2)
interior := totalInterior / float64(sides)
exterior := math.Pi - interior
// Get into position
t.PenUp()
t.Forward(size / 2)
t.Right(math.Pi/2 + exterior/2)
t.PenDown()
// Draw it
for i := 0; i < sides; i++ {
t.Forward(size)
t.Right(exterior)
}
// Get back to where we started
t.PenUp()
t.Left(math.Pi/2 + exterior/2)
t.Backward(size / 2)
t.PenDown()
}
