User guide

DrawTurksHead can be used on the command line or as a Python package.

Command-line

Basic usage:

$ python -m DrawTurksHead --leads=3 --bights=7

For details of available parameters:

$ python -m DrawTurksHead --help

Python package

Import:

>>> import cairo
>>> from DrawTurksHead import TurksHead

Create a Turk’s head:

>>> knot = TurksHead(bights=7, leads=3, inner=50, outer=200, line=30)

Create a Cairo context:

>>> img = cairo.ImageSurface(cairo.FORMAT_RGB24, 440, 440)
>>> ctx = cairo.Context(img)
>>> ctx.set_source_rgb(1, 1, 1)
>>> ctx.paint()
>>> ctx.translate(220, 220)

Draw the Turk’s head on the Cairo context:

>>> knot.draw(ctx)

Draw circles to verify inner and outer radiuses:

>>> ctx.set_source_rgb(0, 0, 1)
>>> ctx.arc(0, 0, 50, 0, 6.30)
>>> ctx.arc(0, 0, 200, 0, 6.30)
>>> ctx.stroke()

Save the result to a file:

>>> img.write_to_png("doc/doctest/1.png")

doc/doctest/1.png

Let’s define a utility method:

>>> def draw_to_png(knot, filename):
...   img = cairo.ImageSurface(cairo.FORMAT_RGB24, 440, 440)
...   ctx = cairo.Context(img)
...   ctx.set_source_rgb(1, 1, 1)
...   ctx.paint()
...   ctx.translate(220, 220)
...   knot.draw(ctx)
...   img.write_to_png(filename)

You can choose the color of the drawing by providing a Colorer:

>>> class MyColorer(object):
...   def compute_color_hsv(self, knot, k, theta, altitude):
...     h = 180 + k * 360 / knot.d
...     s = 1
...     v = .5 + altitude / 2
...     return h, s, v
>>> knot = TurksHead(
...   bights=7, leads=3,
...   inner=50, outer=200, line=30,
...   colorer=MyColorer()
... )
>>> draw_to_png(knot, "doc/doctest/2.png")

doc/doctest/2.png

Or:

>>> from DrawTurksHead import DefaultColorer
>>> class MyColorer(DefaultColorer):
...   def compute_color_hsv(self, knot, k, theta, altitude):
...     h, s, v = super(MyColorer, self).compute_color_hsv(knot, k, theta, altitude)
...     s = 0.25
...     v = v / 2
...     return h, s, v
>>> knot = TurksHead(
...   bights=7, leads=3,
...   inner=50, outer=200, line=30,
...   colorer=MyColorer()
... )
>>> draw_to_png(knot, "doc/doctest/3.png")

doc/doctest/3.png

Or:

>>> import math
>>> class MyColorer(object):
...   def compute_color_rgb(self, knot, k, theta, altitude):
...     assert 0 <= theta < 2 * knot.q_prime * math.pi
...     b = theta / (2 * knot.q_prime * math.pi)
...     return 0, 0, b
>>> knot = TurksHead(
...   bights=7, leads=3,
...   inner=50, outer=200, line=30,
...   colorer=MyColorer()
... )
>>> draw_to_png(knot, "doc/doctest/4.png")

doc/doctest/4.png