Turtle.sf

#!/usr/bin/ruby

require('Image::Magick')

class Turtle(
    x      = 500,
    y      = 500,
    angle  = 0,
    scale  = 1,
    mirror = 1,
    xoff   = 0,
    yoff   = 0,
    color  = 'black',
) {

    has im = %O<Image::Magick>.new(size => "#{x}x#{y}")

    method init {
        angle.deg2rad!
        im.ReadImage('canvas:white')
    }

    method forward(r) {
        var (newx, newy) = (x + r*sin(angle), y + r*-cos(angle))

        im.Draw(
            primitive => 'line',
            points    => join(' ',
                           round(x    * scale + xoff),
                           round(y    * scale + yoff),
                           round(newx * scale + xoff),
                           round(newy * scale + yoff),
                        ),
            stroke      => color,
            strokewidth => 1,
        )

        (x, y) = (newx, newy)
    }

    method save_as(filename) {
        im.Write(filename)
    }

    method turn(theta) {
        angle += theta*mirror
    }

    method state {
        [x, y, angle, mirror]
    }

    method setstate(state) {
        (x, y, angle, mirror) = state...
    }

    method mirror {
        mirror.neg!
    }
}