fractal_tree.py

import colorsys
import math
import random
import cairo

random.seed(10)

WIDTH  = 500
HEIGHT = 500

MAX_ITER = 8
LINE_WIDTH = 0.002

LINE_LEN_MIN = 0.01
LINE_LEN_MAX = 0.2

LINE_DECAY = 0.8

ANGLE_SHIFT_MIN = 0.2 * -math.pi
ANGLE_SHIFT_MAX = 0.2 * math.pi

INIT_LENGTH = 0.05

SPLIT_MIN = 2
SPLIT_MAX = 4

mana_prob = 0.1

def draw_line(ctx, x1, y1, x2, y2, rgb, line_width):
    ctx.move_to(x1, y1)
    ctx.line_to(x2, y2)

    ctx.set_source_rgb(rgb[0], rgb[1], rgb[2])
    ctx.set_line_width(line_width)

    ctx.stroke()

def draw_gem(ctx, x1, y1):
    ctx.move_to(x1, y1)
    ctx.line_to(x1, y1 - 0.01)
    ctx.set_source_rgb(0, 1, 0)
    ctx.set_line_width(0.002)
    ctx.stroke()

    ctx.arc(x1, y1 - 0.01, 0.005, 0, math.pi * 2)
    ctx.set_source_rgb(1, 1, 0)
    ctx.fill()

def fractal_tree(
    ctx, x1, y1, length, rad,
    line_len_min=0.0,
    line_len_max=1.0,
    angle_shift_min=0.2,
    angle_shift_max=0.8,
    split_min=2,
    split_max=4,
    iter=10
):
    x2 = x1 + math.cos(rad) * length
    y2 = y1 + math.sin(rad) * length
    
    draw_line(ctx, x1, y1, x2, y2, (1,1,1), LINE_WIDTH)

    num_split = int((split_max - split_min) * random.random() + split_min)

    if iter > 0:
        for i in range(num_split):
            new_len = (line_len_max - line_len_min) * random.random() + line_len_min
            new_rad = rad + (angle_shift_max - angle_shift_min) * random.random() + angle_shift_min

            fractal_tree(
                ctx, x2, y2, new_len, new_rad,
                line_len_min=line_len_min * LINE_DECAY,
                line_len_max=line_len_max * LINE_DECAY,
                angle_shift_min=angle_shift_min,
                angle_shift_max=angle_shift_max,
                split_min=split_min,
                split_max=split_max,
                iter=iter-1
            )
    else:
        p = random.random()

        if p < mana_prob:
            draw_gem(ctx, x2, y2)

surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, WIDTH, HEIGHT)
ctx = cairo.Context(surface)

ctx.scale(WIDTH, HEIGHT)
ctx.translate(0.5, 0.5)
ctx.rotate(math.pi)
ctx.translate(-0.5, -0.5)

x0 = 0.5
y0 = 0

rad = math.pi / 2

fractal_tree(
    ctx, x0, y0, INIT_LENGTH, rad,
    line_len_min=LINE_LEN_MIN,
    line_len_max=LINE_LEN_MAX,
    angle_shift_min=ANGLE_SHIFT_MIN,
    angle_shift_max=ANGLE_SHIFT_MAX,
    split_min=SPLIT_MIN,
    split_max=SPLIT_MAX,
    iter=MAX_ITER
)

surface.write_to_png('logo.png')