shithub: graphical-algorithms

ref: f5f4fb16ed24308c78ba1fdc5e84cbcaba53c51c
dir: /sierpinski-lsystem/

#!/bin/slug

-- Sierpinski triangle generation using an L-System
-- see https://en.wikipedia.org/wiki/L-system#Example_5:_Sierpinski_triangle

gen = 0
start = "F-G-G"
rules = { F="F-G+F+G-F", G="GG" }
angle = 120
len = 50
current = start
x = 0
y = 0

function setup()
	size(1600, 1400)
end

function evolve()
	gen = gen + 1
	next = ""
	for i = 1, #current do
		c = string.sub(current, i, i)
		r = rules[c]
		if r ~= nil then
			next = next .. r
		else
			next = next .. c
		end
	end
	current = next
end

function draw()
	if gen == 6 then
		noLoop()
		return
	end
	evolve()
	background(0)
	stroke(255)
	strokeWeight(1)
	x = width / 2
	y = height-10
	for i = 1, #current do
		c = string.sub(current, i, i)
		if c == "F" or c == "G" then
			nx = math.floor(0.5 + x + len * math.cos(radians(angle)))
			ny = math.floor(0.5 + y + len * math.sin(radians(angle)))
			line(x, y, nx, ny)
			x = nx
			y = ny
		elseif c == "+" then
			angle = angle - 120
		elseif c == "-" then
			angle = angle + 120
		end
	end
end