Spiral

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To draw a spiral you can reuse the line drawing function:


import numpy as np
from PIL import Image
import math
from lines import draw_line


def spiral(    
        xcenter,
        ycenter,
        angle=0,
        radius=1,
        angle_step=10,
        radius_step=0.7
        ):
    """generates spiral coordinates"""
    while True:
        angle += angle_step
        radius += radius_step
        yield (
            round(math.cos(angle * math.pi / 180) * radius + xcenter),
            round(math.sin(angle * math.pi / 180) * radius + ycenter)
        )


a = np.zeros((400, 400, 3), dtype=np.uint8)
x, y = 200, 200
spiral_gen = spiral(x, y)

for i in range(250):
    xnew, ynew = next(spiral_gen)
    draw_line(a, x, y, xnew, ynew)
    x, y = xnew, ynew

im = Image.fromarray(a)
im.save('spiral.png')

When drawing a spiral it is key to start in the middle. This allows to catch the essential properties of a spiral in code:

  • it rotates in circles

  • the radius of the circle becomes bigger and bigger

  • the spiral is potentially endless

The angle and radius are polar coordinates. You can convert them to cartesian coordinates through trigonometric functions. A generator function is a good solution to model a potentially endless spiral. The line drawing function takes care of the rest.

Challenge

Become creative with the spiral function:

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