DrawBot: Generate a progress-spinner-like animation with growing circles.

GrowingCircles.py

# Result:
# http://dailydrawbot.tumblr.com/post/150807743869/growing-circles

def circle(pt, radius):
    diameter = 2 * radius
    x, y = pt
    oval(x - radius, y - radius, diameter, diameter)

nFrames = 50
canvasSize = 500
radius = 0.27 * canvasSize
nCircles = 12

for i in range(nFrames):
    framePhase = i / nFrames

    newPage(canvasSize, canvasSize)
    frameDuration(1/20)

    fill(0)
    rect(0, 0, canvasSize, canvasSize)
    translate(canvasSize/2, canvasSize/2)

    for i in range(nCircles):
        circlePhase = i / nCircles
        a = 2 * pi * circlePhase
        x = radius * cos(a)
        y = radius * sin(a)
        cr = ((circlePhase + framePhase) % 1)
        fill(1, (1 - cr) ** 0.7)
        circle((x, y), cr * 110)

saveImage("GrowingCircles.gif")