Rotating arrows exercise

justvanrossum

This is by no means an original idea, but it's a fun thing to program.

Triggered by Mike Duggan: https://twitter.com/mickduggan/status/1090577885067386880

# triggered by Mike Duggan:
# https://twitter.com/mickduggan/status/1090577885067386880

def arrow(center, size, rotation, barThickness, arrowhead):
    with savedState():
        translate(*center)
        scale(size)
        rotate(rotation)
        points = [
            (-0.5, barThickness/2),
            (0.5 - arrowhead, barThickness/2),
            (0.5 - arrowhead, 0.5),
            (0.5, 0),
            (0.5 - arrowhead, -0.5),
            (0.5 - arrowhead, -barThickness/2),
            (-0.5, -barThickness/2),
        ]
        polygon(*points)

def arrowGrid(numArrows, arrowSize, barThickness, arrowhead, rotation):
    for i in range(numArrows):
        x = i * arrowSize
        for j in range(numArrows):
            y = j * arrowSize
            arrow((x, y), arrowSize, rotation, barThickness, arrowhead)

def easeInOut(t):
    assert 0 <= t <= 1
    return (1 - cos(t * pi)) / 2

canvasSize = 400
numArrows = 4
arrowSize = canvasSize / numArrows
barThickness = 0.5
arrowhead = 0.5
rotation = 180

duration = 4
framesPerSecond = 15
numFrames = duration * framesPerSecond

for frame in range(numFrames):
    t = 4 * frame / numFrames
    quadrant = floor(t)
    t = easeInOut(t % 1)
    angle = ((quadrant + t) * 90) % 380
    flip = quadrant % 2
    angle = -angle

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

    if flip:
        fill(1)
        rect(0, 0, canvasSize, canvasSize)
        fill(0)
        arrowGrid(numArrows + 1, arrowSize, barThickness, arrowhead, angle)
    else:
        fill(0)
        rect(0, 0, canvasSize, canvasSize)
        fill(1)
        translate(-arrowSize/2, -arrowSize/2)
        arrowGrid(numArrows + 2, arrowSize, 1 - barThickness, arrowhead, angle + 180)

saveImage("Arrows.gif")