barnsley_fern_ifs.sf

#!/usr/bin/ruby

# Code from a lesson by Keith Peters.
# See: https://www.youtube.com/watch?v=geqq63WFLr0

require('Imager')

var (width, height) = (500, 500)
var img = %O<Imager>.new(xsize => width, ysize => height)

struct Rule {
    a, b, c, d, tx, ty, w
}

var rules = [
    Rule(
        a: 0.85,
        b: 0.04,
        c: -0.04,
        d: 0.85,
        tx: 0,
        ty: 1.6,
        w: 0.85,
    ),
    Rule(
        a: -0.15,
        b: 0.28,
        c: 0.26,
        d: 0.24,
        tx: 0,
        ty: 0.44,
        w: 0.07,
    ),
    Rule(
        a: 0.2,
        b: -0.26,
        c: 0.23,
        d: 0.22,
        tx: 0,
        ty: 1.6,
        w: 0.07,
    ),
    Rule(
        a: 0,
        b: 0,
        c: 0,
        d: 0.16,
        tx: 0,
        ty: 0,
        w: 0.01,
    )
]

func plot(x, y) {
    static green = %O<Imager::Color>.new('#00ff00')
    img.setpixel(
        x     => width/2 + Math.map(2*x, 0, 10, 0, width/2),
        y     => height  - Math.map(2*y, 0, 10, 0, height/2),
        color => green
    )
}

func getRule {
    var r = 1.rand
    for rule in (rules) {
        if (r < rule.w) {
            return rule
        }
        r -= rule.w
    }
}

var (x, y) = 2.of { 1.rand }...

var iterate = {
    var rule = getRule()

    var x1 = (x*rule.a + y*rule.b + rule.tx)
    var y1 = (x*rule.c + y*rule.d + rule.ty)

    x = x1
    y = y1

    plot(x, y)
}

iterate * 2000
img.write(file => 'barnsley_fern.png')