# Interference Patterns (PyGame)

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If you draw shapes that are closely spaced and shifted, you can create interesting interference patterns, so called moire patterns. Here is an example using the Python module PyGame to do the drawing.

``````''' pg_moire_patterns2.py
create moire patterns using Python module pygame
draws closely spaced and shifted circles that create
an interference pattern often seen in silk textiles
tested with Python27/Python33 and PyGame192
'''

import pygame as pg
import random
import math

#screen width, height, diagonal
width = 400
height = 400
diag = math.sqrt(width**2 + height**2)

# colors in r,g,b values 0 to 255
white = 255, 255, 255
color = 46, 139, 87  # seagreen

screen = pg.display.set_mode((width, height))
pg.display.set_caption("Moire Patterns")
screen.fill(white)

# pos, xMov, yMov, spacing values
circles = []
for i in range(3):
pos = [random.randint(0, width-1), random.randint(0, height-1)]
xMov = random.randint(1, 3)
yMov = random.randint(1, 3)
spacing = random.randint(3, 3)
circles.append([pos, xMov, yMov, spacing])

clock = pg.time.Clock()
# exit on escape or window corner x click
while True:
for event in pg.event.get():
if event.type == pg.QUIT:
# most reliable exit on x click
pg.quit()
raise SystemExit
elif event.type == pg.KEYDOWN:
# optional exit with escape key
if event.key == pg.K_ESCAPE:
pg.quit()
raise SystemExit

screen.fill(white)

for c in circles:
r = c[3]
while r < diag:
pg.draw.circle(screen, color, c[0], r, 1)
r += c[3]
pg.display.flip()
clock.tick(20)

for c in circles:
c[0][0] += c[1]
if c[0][0] < 0 or c[0][0] >= width:
c[1] *= -1
c[0][0] += c[1]
c[0][1] += c[2]
if c[0][1] < 0 or c[0][1] >= height:
c[2] *= -1
c[0][1] += c[2]``````
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