patterns — nested

def g14_nested(rng):
    """Concentric squares inside each cell, stepping along the ramp."""
    steps = rng.randint(5, 8)
    N = rng.choice([25, 30])
    c = Canvas(N, _pal(rng), steps, "nested", "squares")
    f = Field(rng, rng.choice(["linear", "mesh"]), warp=rng.uniform(0.2, 0.45), steps=steps)
    c.ground_from(f)
    C = c.C
    for j in range(N):
        for i in range(N):
            u, v = c.uv(i, j)
            base = f.idx(u, v)
            rings = 1 + int(f.raw(u, v) * 3)
            for r in range(1, rings):
                ins = r * C / (2 * rings)
                c.sq(i * C + ins, j * C + ins, C - 2 * ins, C - 2 * ins, (base + r) % steps)
    return c