patterns — spindrift

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source — auto/a005_spindrift.g55_spindrift
def g55_spindrift(rng):
    """SPIN DRIFT — triangles rotated to face a vortex centre, scaled by radius.
    A logarithmic term in the angle pulls the whole field into a spiral. One or
    two weaker secondary vortices, each with a fraction of the primary's pull
    and a limited reach, bend the field locally without overpowering it."""
    N = 24
    c = Canvas(N, "GEOMETRIC", "tri", "spindrift", tiles=False)
    C = c.C
    cx, cy = rng.uniform(.25, .75), rng.uniform(.25, .75)
    spin = rng.uniform(-90, 90)
    twist = rng.uniform(20, 140) * rng.choice([1, -1])
    grow = rng.uniform(0.55, 1.15)

    extras = []
    for _ in range(rng.randint(1, 2)):
        vx, vy = rng.uniform(0.1, 0.9), rng.uniform(0.1, 0.9)
        pull = rng.uniform(0.15, 0.4)     # fraction of the primary vortex's pull
        reach = rng.uniform(0.15, 0.32)   # influence fades to zero past this radius
        extras.append((vx, vy, pull, reach))

    for i in range(N):
        for j in range(N):
            u, v = (i + 0.5) / N, (j + 0.5) / N
            dx, dy = u - cx, v - cy
            d = math.hypot(dx, dy) + 1e-6
            wx, wy = dx / d, dy / d
            for vx, vy, pull, reach in extras:
                edx, edy = u - vx, v - vy
                ed = math.hypot(edx, edy) + 1e-6
                fall = clamp(1 - ed / reach)
                if fall <= 0:
                    continue
                w = pull * fall
                wx += w * edx / ed
                wy += w * edy / ed
            a = math.degrees(math.atan2(wy, wx)) + spin + twist * math.log(d + 0.12)
            r = 0.46 * C * clamp(0.42 + grow * d * 1.3)
            x, y = c.center(i, j)
            c.tri(x, y, r, rot=a)
    return c
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