music-video-gen/flow-state/src/scenes/shader/aqueduct-march.js

// Structural family: an aqueduct marching away across the frame — a lower tier
// of wide piers, an upper tier of small fast ones, and daylight through every
// opening.
//
// Pylon Grid is open frame: you see through the whole structure and it has no
// mass. This is masonry. The wall is solid, the light comes through holes cut in
// it, and the rhythm changes tier to tier — two arches up top for every one
// below, which is the thing that makes a real aqueduct read as marching rather
// than repeating. The openings are the track's signature form, so a hexagonal
// video is an aqueduct of hexagons.
//
// No declared slow axis, for the reason Contour Map and Balance Stack give: the
// candidates were measured — tier height 0.91x, opening size 0.62x, tier count
// 0.17x — and none of them beats the camera's own drift in Phase 11's
// ten-second average. The structure is legible because it is high-contrast and
// mostly still, and that is exactly the kind of image where a slow parameter
// walk moves less of the frame than a slow pan does.

export const aqueductMarch = {
    name: 'Aqueduct March',
    family: 'structural',
    kind: 'fragment',
    texture: 0.9,
    consumes: ['cast', 'ink'],
    traits: ['shape', 'camera', 'space', 'style'],

    params: {
        bays:    { type: 'float', range: [1.2, 6],     default: 2.2,  uniform: 'u_bays', bias: 'density' },
        opening: { type: 'float', range: [0.18, 0.6],  default: 0.42, uniform: 'u_opening' },
        tiers:   { type: 'int',   range: [1, 4],       default: 2,    uniform: 'u_tiers' },
        rise:    { type: 'float', range: [0.3, 1.3],   default: 0.7,   uniform: 'u_rise' },
        recede:  { type: 'float', range: [0, 0.8],     default: 0.35, uniform: 'u_recede' },
        sun:     { type: 'float', range: [0, 1.5],     default: 0.7,  uniform: 'u_sunlight', bias: 'energy' },
        march:   { type: 'float', range: [0.005, 0.2], default: 0.04, uniform: 'u_march', bias: 'motion', rate: true },
        palette: { type: 'palette', count: 5 },
    },

    reactive: {
        sun:    { feature: 'loudness', amount: 0.3,  response: 'smooth' },
        recede: { feature: 'bandLow',  amount: 0.15, response: 'smooth' },
    },

    shader: `
// One tier of masonry: a wall with a row of openings cut through it. Returns
// how much of this pixel is stone.
float tier(vec2 q, float bays, float top, float bottom, float shift) {
    if (q.y > top || q.y < bottom) return 0.0;
    float h = top - bottom;
    float g = q.x * bays + shift;
    float cx = (fract(g) - 0.5) / bays;

    // The opening is sized as a FRACTION OF ITS BAY in both directions, not as
    // a circle of some radius: a bay is much wider than it is tall once there
    // are three of them across the frame, and a round hole in it is a porthole
    // rather than an arch. Sized this way the same number reads as the same
    // opening whatever the bay count is.
    float cw = 0.5 / bays;                  // half a bay across
    float ch = h * 0.4;                     // half an opening up
    float k = u_opening * 2.4;
    vec2 local = vec2(cx / max(cw * k, 1e-4),
                      (q.y - (bottom + h * 0.46)) / max(ch * k, 1e-4));

    // The opening sits low in the tier, leaving a solid band above it to carry
    // the next tier — which is the whole structural point of an aqueduct.
    float hole = castMain(local) * min(cw, ch) * k;
    return smoothstep(-0.004, 0.004, hole);
}

vec4 scene(vec2 uv, vec2 p) {
    float t = u_time * u_march + u_seed;
    p = sigCamera(p);

    float horizon = sigHorizonY() * 0.35 - 0.1;

    // Sky behind the structure, and the ground it stands on.
    vec3 col = mix(pal(1) * 0.22, pal(0) * 0.05, sat((p.y - horizon) * 0.7 + 0.2));
    col += pal(3) * exp(-abs(p.y - horizon) * 5.0) * u_sunlight * 0.5;
    col = mix(col, pal(0) * 0.1, smoothstep(horizon + 0.01, horizon - 0.05, p.y));

    // Two ranges of the same structure: the far one smaller, slower and hazier,
    // so the aqueduct crosses a valley rather than standing in a diagram.
    // lint: fixed-cost — a near range and a far one
    for (int k = 0; k < 2; k++) {
        float fk = float(k);
        float scale = mix(1.0, 0.35, fk * u_recede * 2.0);
        float lift = horizon + fk * u_recede * 0.25;

        vec2 q = vec2(p.x / max(scale, 0.15), (p.y - lift) / max(scale, 0.15));
        float shift = t * mix(1.0, 0.35, fk);

        float stone = 0.0;
        float base = 0.0;
        // lint: fixed-cost — at most four tiers
        for (int i = 0; i < 4; i++) {
            if (i >= u_tiers) break;
            float fi = float(i);
            float bottom = fi * u_rise;
            float top = bottom + u_rise;
            // Each tier up is twice as fine and half as tall a rhythm.
            stone = max(stone, tier(q, u_bays * pow(2.0, fi), top, bottom,
                                    shift * pow(2.0, fi) + fi * 0.31));
            base = max(base, step(bottom, q.y) * step(q.y, top));
        }

        // Stone: lit from the sun side, shadowed on the other, courses picked
        // out by a horizontal banding that survives the perspective.
        // Courses are drawn in the track's hand: heavy for a track with a thick
        // line, barely there for a fine one.
        float course = 0.5 + 0.5 * sin(q.y * 60.0);
        course = mix(course, smoothstep(0.35, 0.75, course), u_sigLine);
        vec3 masonry = mix(pal(2) * 0.35, pal(4) * 0.8, sat(q.x * 0.4 + 0.5));
        masonry *= 0.7 + (0.15 + u_sigLine * 0.5) * course;
        masonry += pal(3) * u_sunlight * 0.22 * sat(q.x * 0.5 + 0.5);
        masonry += pal(4) * inkStroke(0.5 - abs(fract(q.x * u_bays) - 0.5) - 0.03) * (0.1 + u_sigLine * 0.9);

        float hazed = mix(1.0, 0.55, fk * u_recede);
        col = mix(col, masonry * hazed, stone * base);
    }

    col = sigAir(col, p, smoothstep(-0.2, 0.9, p.y - horizon));
    return vec4(inkValue(col), 1.0);
}
`,
};

export default aqueductMarch;