patterns — flowfield

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source — gen_a.g02_flowfield
def g02_flowfield(rng):
    """FLOW FIELD — one segment per cell, angle from a summed sine field,
    weight from the field's rate of change. Fast-turning regions go heavy."""
    N = 40
    c = Canvas(N, "GEOMETRIC", "lines", "flowfield", tiles=False)
    C = c.C
    k1, k2 = rng.uniform(1.5, 4.0), rng.uniform(1.5, 4.0)
    sw_ = rng.uniform(0.4, 1.6)
    off = rng.uniform(0, math.tau)

    def theta(u, v):
        return (math.sin(u * k1 * math.tau + off) * 1.4
                + math.cos(v * k2 * math.tau) * 1.1
                + math.sin((u + v) * sw_ * math.tau) * 0.8)

    L = C * rng.uniform(1.15, 1.75)
    for i in range(N):
        for j in range(N):
            u, v = (i + 0.5) / N, (j + 0.5) / N
            a = theta(u, v)
            d = abs(theta(u + 1.0 / N, v) - a) + abs(theta(u, v + 1.0 / N) - a)
            w = 0.06 + 0.34 * clamp(d * 3.0)
            x, y = c.center(i, j)
            c.line(x, y, L, math.degrees(a), sw=w * C, cap="round")
    return c
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