zigzag.osl

float fract(float a) {
    return a - floor(a);
}
point fract(point p) {
    return point(fract(p[0]), fract(p[1]), fract(p[2]));
}
float lerp(float a, float b, float t) {
    return (1 - t) * a + t * b;
}

float hash21(point p) {
    p = fract(p*point(123.34, 456.21, 0.));
    p += dot(p, p+45.32);
    return fract(p[0] * p[1]);
}

shader zigzag(
    point p = P,
    float scale = 1.,
    float scale_y = 1.,
    float add_y = 1.,
    output color Color = (0.0),
) {
    int id_x = int(p[0] * scale);
    float x = fract(p[0] * scale);
    float y = (p[1] + add_y) * scale_y;
    float z = p[2];

    int up_or_down = id_x % 2;
    point cur;
    point prev;

    if (up_or_down) {
        cur = hash21(point(id_x, id_x, id_x)) * -1;
        prev = hash21(point(id_x-1, id_x-1, id_x-1));
    } else {
        cur = hash21(point(id_x, id_x, id_x));
        prev = hash21(point(id_x-1 , id_x-1, id_x-1)) * -1;
    }

    y += lerp(prev[0]-.5, cur[0]-.5, x);

    Color = y;
}