spirotri

#!/usr/bin/python3
#+
# My attempt to create patterns like those published in
# BYTE Magazine of September 1978, pages 40-46
# <https://archive.org/details/byte-magazine-1978-09>.
# Another potentially interesting one is in the issue
# of November 1982, page 119
# <https://archive.org/details/byte-magazine-1982-11>.
#
# Copyright 2016, 2018 by Lawrence D'Oliveiro <ldo@geek-central.gen.nz>. This
# script is licensed CC0
# <https://creativecommons.org/publicdomain/zero/1.0/>; do with it
# what you will.
#-

import sys
import os
import math
import qahirah as qah
from qahirah import \
    CAIRO, \
    Colour, \
    Matrix, \
    Vector

triangle_corners = list(Vector(1, 0).rotate(a / 3 * qah.circle) for a in range(3))
triangle_step = Vector(1.5, math.sqrt(3) / 2)
flip_adjust = Vector(0.5, 0)

pix_size = 700
figure_size = 150
pix = qah.ImageSurface.create \
  (
    format = CAIRO.FORMAT_ARGB32,
    dimensions = round(Vector(1, 1) * pix_size)
  )
ctx = \
    (qah.Context.create(pix)
        .translate(Vector(0.5, 0.5) * pix_size)
        .set_source_colour(Colour.grey(1))
        .paint()
        .set_source_colour(Colour.grey(0))
        .set_line_width(2)
    )

def draw_cell(ctx, angle, colours) :
    with ctx.save_state() :
        ctx.transform(Matrix.rotate(angle) * Matrix.scale(figure_size))
        scale_step = 0.87
        ctx.line_width /= figure_size # compensate for scaling of entire coordinate system
        for step in range(15) :
            for i in range(3) :
                (ctx
                    .new_path()
                    .move_to(triangle_corners[i - 1])
                    .line_to(triangle_corners[i])
                    .set_source_colour(colours[i])
                    .stroke()
                )
            #end for
            ctx.transform \
              (
                Matrix.rotate(5 * qah.deg) * Matrix.scale(scale_step)
              )
            ctx.line_width /= scale_step
        #end for
    #end with
#end draw_cell

for row in range(-3, 4) :
    for col in range(-2, 2) :
        flip = (row ^ col) & 1
        with ctx.save_state() :
            ctx.translate \
              (
                (Vector(col, row) * triangle_step + flip_adjust * flip) * figure_size
              )
            draw_cell \
              (
                ctx = ctx,
                angle = flip * 180 * qah.deg,
                colours =
                    [
                        Colour.from_hsva((0.55, 0.5, 0.4)),
                        Colour.from_hsva((0.05, 0.5, 0.4)),
                        Colour.from_hsva((0.8, 0.5, 0.4)),
                    ]
              )
        #end with
    #end for
#end for

pix.flush().write_to_png("%s.png" % os.path.basename(sys.argv[0]))