//! Simulation effects, part 2: layer-shattering and surface simulations — CC Ball Action,
//! CC Pixel Polly, CC Scatterize, Card Dance, Shatter (planar pieces in perspective), Caustics,
//! Wave World (stepped 2D wave equation) and Foam (stepped bubble sim).
//!
//! Written from the public descriptions of the effects' behaviour. Pieces are textured convex
//! polygons placed in 3D and drawn through a per-piece inverse homography, far to near.

use effectcraft_keyframe::Value;
use effectcraft_project::ParamUi;
use effectcraft_raster::{Image, Px};
use rayon::prelude::*;

use crate::generate::value_noise;
use crate::sim::{Acc, Shape, Sprite, h, hs, pct, pt, raster, spec, splat};
use crate::util::{Plane, SimCache, gauss_plane, layer_or_self, params_key, unpremul};
use crate::{Buf, EffectCtx, EffectSpec, col, num, p, popup, slider};

// ------------------------------------------------------------------ 3D pieces

type M3 = [[f64; 3]; 3];

fn mat_mul(a: &M3, b: &M3) -> M3 {
    std::array::from_fn(|i| std::array::from_fn(|j| (0..3).map(|k| a[i][k] * b[k][j]).sum()))
}

/// Rotation from Euler angles (radians), applied X then Y then Z.
fn rot_xyz(x: f64, y: f64, z: f64) -> M3 {
    let (sx, cx) = x.sin_cos();
    let (sy, cy) = y.sin_cos();
    let (sz, cz) = z.sin_cos();
    let rx = [[1.0, 0.0, 0.0], [0.0, cx, -sx], [0.0, sx, cx]];
    let ry = [[cy, 0.0, sy], [0.0, 1.0, 0.0], [-sy, 0.0, cy]];
    let rz = [[cz, -sz, 0.0], [sz, cz, 0.0], [0.0, 0.0, 1.0]];
    mat_mul(&rz, &mat_mul(&ry, &rx))
}

/// Rotation by `angle` about unit `axis` (Rodrigues).
fn rot_axis(axis: [f64; 3], angle: f64) -> M3 {
    let l = (axis[0] * axis[0] + axis[1] * axis[1] + axis[2] * axis[2]).sqrt();
    if l < 1e-12 || angle == 0.0 {
        return [[1.0, 0.0, 0.0], [0.0, 1.0, 0.0], [0.0, 0.0, 1.0]];
    }
    let (x, y, z) = (axis[0] / l, axis[1] / l, axis[2] / l);
    let (s, c) = angle.sin_cos();
    let t = 1.0 - c;
    [
        [t * x * x + c, t * x * y - s * z, t * x * z + s * y],
        [t * x * y + s * z, t * y * y + c, t * y * z - s * x],
        [t * x * z - s * y, t * y * z + s * x, t * z * z + c],
    ]
}

fn inv3(m: &M3) -> Option<M3> {
    let det = m[0][0] * (m[1][1] * m[2][2] - m[1][2] * m[2][1]) - m[0][1] * (m[1][0] * m[2][2] - m[1][2] * m[2][0])
        + m[0][2] * (m[1][0] * m[2][1] - m[1][1] * m[2][0]);
    if det.abs() < 1e-12 {
        return None;
    }
    let d = 1.0 / det;
    Some([
        [(m[1][1] * m[2][2] - m[1][2] * m[2][1]) * d, (m[0][2] * m[2][1] - m[0][1] * m[2][2]) * d, (m[0][1] * m[1][2] - m[0][2] * m[1][1]) * d],
        [(m[1][2] * m[2][0] - m[1][0] * m[2][2]) * d, (m[0][0] * m[2][2] - m[0][2] * m[2][0]) * d, (m[0][2] * m[1][0] - m[0][0] * m[1][2]) * d],
        [(m[1][0] * m[2][1] - m[1][1] * m[2][0]) * d, (m[0][1] * m[2][0] - m[0][0] * m[2][1]) * d, (m[0][0] * m[1][1] - m[0][1] * m[1][0]) * d],
    ])
}

/// Perspective camera looking down +z at the layer plane z = 0, `d` pixels away, centred on
/// `c` (buffer pixels): screen = c + (P - c) · d / (d + z).
#[derive(Clone, Copy)]
struct Cam {
    c: [f64; 2],
    d: f64,
}

/// A planar textured piece ready to draw.
#[derive(Clone, Copy)]
struct Piece {
    /// Screen (buffer px, homogeneous) → piece-local (a, b, w).
    inv: M3,
    /// Rest centre of the piece in texture pixels.
    c0: [f32; 2],
    /// Convex polygon (texture pixels), counter-clockwise in y-down space.
    poly: [[f32; 2]; 6],
    n: u8,
    bbox: [f32; 4],
    shade: f32,
    alpha: f32,
    /// Flat straight colour instead of the texture.
    flat: Option<[f32; 3]>,
    /// Facing away from the camera (draw the back texture).
    back: bool,
    depth: f64,
}

impl Piece {
    /// Place polygon `poly` (texture px, around rest centre `c0`) with rotation `r` and its
    /// centre at 3D `pos` (buffer px; z away from the camera).
    fn new(poly: &[[f32; 2]], c0: [f32; 2], r: &M3, pos: [f64; 3], cam: Cam) -> Option<Piece> {
        let n = poly.len().min(6);
        if n < 3 {
            return None;
        }
        let (cx, cy, d) = (cam.c[0], cam.c[1], cam.d);
        let zc = pos[2];
        let hm: M3 = [
            [cx * r[2][0] + d * r[0][0], cx * r[2][1] + d * r[0][1], cx * (d + zc) + d * (pos[0] - cx)],
            [cy * r[2][0] + d * r[1][0], cy * r[2][1] + d * r[1][1], cy * (d + zc) + d * (pos[1] - cy)],
            [r[2][0], r[2][1], d + zc],
        ];
        let mut bb = [f32::INFINITY, f32::INFINITY, f32::NEG_INFINITY, f32::NEG_INFINITY];
        for v in &poly[..n] {
            let (a, b) = ((v[0] - c0[0]) as f64, (v[1] - c0[1]) as f64);
            let w = hm[2][0] * a + hm[2][1] * b + hm[2][2];
            if w < d * 0.05 {
                return None;
            }
            let sx = ((hm[0][0] * a + hm[0][1] * b + hm[0][2]) / w) as f32;
            let sy = ((hm[1][0] * a + hm[1][1] * b + hm[1][2]) / w) as f32;
            bb = [bb[0].min(sx), bb[1].min(sy), bb[2].max(sx), bb[3].max(sy)];
        }
        let inv = inv3(&hm)?;
        let mut pp = [[0.0f32; 2]; 6];
        pp[..n].copy_from_slice(&poly[..n]);
        // Normalise winding so "inside" is cross >= 0 for every edge.
        let area: f32 = (0..n).map(|i| pp[i][0] * pp[(i + 1) % n][1] - pp[(i + 1) % n][0] * pp[i][1]).sum();
        if area < 0.0 {
            pp[..n].reverse();
        }
        // Front normal (0, 0, -1) rotated; facing the camera when its z is negative.
        let nz = -r[2][2];
        Some(Piece {
            inv,
            c0,
            poly: pp,
            n: n as u8,
            bbox: [bb[0] - 1.0, bb[1] - 1.0, bb[2] + 1.0, bb[3] + 1.0],
            shade: 1.0,
            alpha: 1.0,
            flat: None,
            back: nz > 0.0,
            depth: zc,
        })
    }

    /// Lambert factor of the piece normal against a light shining along +z.
    fn facing(r: &M3) -> f32 {
        r[2][2].abs() as f32
    }
}

/// Draw pieces (already sorted far → near) over `out`.
fn draw_pieces(out: &mut Image, pieces: &[Piece], front: &Image, back: Option<&Image>) {
    raster(
        out,
        pieces,
        |q| Some(q.bbox),
        |q, x, y| {
            let (xf, yf) = (x as f64, y as f64);
            let m = &q.inv;
            let w = m[2][0] * xf + m[2][1] * yf + m[2][2];
            if w.abs() < 1e-12 {
                return None;
            }
            let u = ((m[0][0] * xf + m[0][1] * yf + m[0][2]) / w) as f32 + q.c0[0];
            let v = ((m[1][0] * xf + m[1][1] * yf + m[1][2]) / w) as f32 + q.c0[1];
            let n = q.n as usize;
            let mut md = f32::INFINITY;
            for i in 0..n {
                let a = q.poly[i];
                let b = q.poly[(i + 1) % n];
                let (ex, ey) = (b[0] - a[0], b[1] - a[1]);
                let l = (ex * ex + ey * ey).sqrt().max(1e-6);
                md = md.min((ex * (v - a[1]) - ey * (u - a[0])) / l);
            }
            // Coverage extends half a pixel past the edge so abutting pieces leave no seams.
            let cov = (md + 1.0).clamp(0.0, 1.0);
            if cov <= 0.0 {
                return None;
            }
            let (c, a) = match q.flat {
                Some(c) => (c, 1.0),
                None => {
                    let tex = if q.back { back.unwrap_or(front) } else { front };
                    unpremul(tex.sample_bilinear(u as f64, v as f64))
                }
            };
            let a = a * cov * q.alpha;
            if a <= 1e-6 {
                return None;
            }
            let k = q.shade;
            Some([c[0] * k * a, c[1] * k * a, c[2] * k * a, a])
        },
        Acc::Over,
    );
}

fn sort_far_first(pieces: &mut [Piece]) {
    pieces.sort_by(|a, b| b.depth.total_cmp(&a.depth));
}

// ------------------------------------------------------------------ CC Ball Action

fn ball_action(ctx: &EffectCtx, mut b: Buf) -> Buf {
    let pr = ctx.params;
    let scatter = pr.f("scatter") as f32;
    let axis = pr.e("rotationAxis");
    let rot = pr.f("rotation").to_radians();
    let twist_prop = pr.e("twistProperty");
    let twist = pr.f("twistAngle").to_radians();
    let spacing = pr.f("gridSpacing").max(1.0) as f32;
    let size = pr.f("ballSize") as f32 / 100.0;
    let instab = pr.f("instabilityState").to_radians() as f32;
    let seed = ctx.seed.wrapping_mul(0x2545f491);
    let (lw, lh) = (ctx.layer_size[0] as f32, ctx.layer_size[1] as f32);
    let s = b.scale as f32;
    let nx = (lw / spacing).ceil().max(1.0) as u32;
    let ny = (lh / spacing).ceil().max(1.0) as u32;
    let d = 2.0 * lw.max(lh) as f64;
    let (cx, cy) = (lw as f64 * 0.5, lh as f64 * 0.5);
    let src = b.img.clone();
    let ax: [f64; 3] = match axis {
        0 => [1.0, 0.0, 0.0],
        1 => [0.0, 1.0, 0.0],
        2 => [0.0, 0.0, 1.0],
        3 => [1.0, 1.0, 0.0],
        4 => [1.0, 0.0, 1.0],
        5 => [0.0, 1.0, 1.0],
        _ => [1.0, 1.0, 1.0],
    };
    let maxr = ((lw * lw + lh * lh).sqrt() * 0.5).max(1.0);
    let mut balls: Vec<(f64, Sprite)> = (0..nx * ny)
        .into_par_iter()
        .filter_map(|i| {
            let gx = (i % nx) as f32 * spacing + spacing * 0.5;
            let gy = (i / nx) as f32 * spacing + spacing * 0.5;
            let (sx, sy) = b.to_px([gx as f64, gy as f64]);
            let (c, a) = unpremul(src.sample_bilinear(sx, sy));
            if a <= 0.0 || size <= 0.0 {
                return None;
            }
            let tp = match twist_prop {
                0 => gx / lw.max(1.0),
                1 => gy / lh.max(1.0),
                2 => ((gx - cx as f32).hypot(gy - cy as f32)) / maxr,
                _ => crate::util::rgb3([c[0], c[1], c[2], 0.0]).iter().sum::<f32>() / 3.0,
            } as f64;
            let ang = rot + twist * tp;
            // Scatter: random 3D offsets whose direction drifts with the instability state.
            let ph = h(i, 1, seed) * std::f32::consts::TAU + instab;
            let sc = scatter * h(i, 2, seed);
            let off = [(sc * ph.cos()) as f64, (sc * ph.sin()) as f64, (scatter * hs(i, 3, seed)) as f64];
            let p0 = [gx as f64 - cx + off[0], gy as f64 - cy + off[1], off[2]];
            let m = rot_axis(ax, ang);
            let q: [f64; 3] = std::array::from_fn(|k| m[k][0] * p0[0] + m[k][1] * p0[1] + m[k][2] * p0[2]);
            if d + q[2] <= d * 0.05 {
                return None;
            }
            let persp = d / (d + q[2]);
            let (bx, by) = b.to_px([cx + q[0] * persp, cy + q[1] * persp]);
            let r = spacing * 0.5 * size * persp as f32 * s;
            Some((q[2], Sprite::new(bx as f32, by as f32, r, [c[0], c[1], c[2], a], Shape::Sphere)))
        })
        .collect();
    balls.sort_by(|a, b| b.0.total_cmp(&a.0));
    let sprites: Vec<Sprite> = balls.into_iter().map(|(_, s)| s).collect();
    b.img = splat(src.width, src.height, &sprites, Acc::Over);
    b
}

// ------------------------------------------------------------------ CC Pixel Polly

fn pixel_polly(ctx: &EffectCtx, mut b: Buf) -> Buf {
    let pr = ctx.params;
    let t = ctx.time - pr.f("startTime");
    if t <= 0.0 {
        return b;
    }
    let force = pr.f("force");
    let gravity = pr.f("gravity");
    let spin = pr.f("spinning").to_radians();
    let fc = pr.v2("forceCenter");
    let dir_rand = pr.f("directionRandomness") / 100.0;
    let spd_rand = pr.f("speedRandomness") / 100.0;
    let g = pr.f("gridSpacing").max(1.0);
    let object = pr.e("object");
    let depth_sort = pr.b("enableDepthSort");
    let seed = ctx.seed.wrapping_mul(0x632be5ab);
    let [lw, lh] = ctx.layer_size;
    let s = b.scale;
    let cam = Cam { c: [b.offset[0] + lw * 0.5 * s, b.offset[1] + lh * 0.5 * s], d: 2.0 * lw.max(lh) * s };
    let nx = (lw / g).ceil().max(1.0) as u32;
    let ny = (lh / g).ceil().max(1.0) as u32;
    let tri = object <= 1;
    let textured = object == 1 || object == 3;
    let maxd = lw.max(lh);
    let src = b.img.clone();
    let per = if tri { 2 } else { 1 };
    let mut pieces: Vec<Piece> = (0..nx * ny * per)
        .into_par_iter()
        .filter_map(|i| {
            let cell = i / per;
            let (x0, y0) = ((cell % nx) as f64 * g, (cell / nx) as f64 * g);
            let poly: Vec<[f64; 2]> = if !tri {
                vec![[x0, y0], [x0 + g, y0], [x0 + g, y0 + g], [x0, y0 + g]]
            } else if i % 2 == 0 {
                vec![[x0, y0], [x0 + g, y0], [x0, y0 + g]]
            } else {
                vec![[x0 + g, y0], [x0 + g, y0 + g], [x0, y0 + g]]
            };
            let c = [poly.iter().map(|v| v[0]).sum::<f64>() / poly.len() as f64, poly.iter().map(|v| v[1]).sum::<f64>() / poly.len() as f64];
            let (dx, dy) = (c[0] - fc[0], c[1] - fc[1]);
            let dist = (dx * dx + dy * dy).sqrt().max(1e-6);
            let ang = dy.atan2(dx) + dir_rand * std::f64::consts::PI * hs(i, 1, seed) as f64;
            let speed = force / 100.0 * 0.6 * maxd / (1.0 + dist / (0.5 * maxd)) * (1.0 + spd_rand * hs(i, 2, seed) as f64);
            let vz = -speed * 0.5 * h(i, 3, seed) as f64;
            let pos = [c[0] + ang.cos() * speed * t, c[1] + ang.sin() * speed * t + 0.5 * gravity * 0.5 * lh * t * t, vz * t];
            let axis = [hs(i, 4, seed) as f64, hs(i, 5, seed) as f64, hs(i, 6, seed) as f64];
            let r = rot_axis(axis, t * (std::f64::consts::PI * h(i, 7, seed) as f64 + spin));
            let tex: Vec<[f32; 2]> = poly.iter().map(|v| [(v[0] * s + b.offset[0]) as f32, (v[1] * s + b.offset[1]) as f32]).collect();
            let c0 = [(c[0] * s + b.offset[0]) as f32, (c[1] * s + b.offset[1]) as f32];
            let posb = [pos[0] * s + b.offset[0], pos[1] * s + b.offset[1], pos[2] * s];
            let mut pc = Piece::new(&tex, c0, &r, posb, cam)?;
            pc.shade = 0.35 + 0.65 * Piece::facing(&r);
            if !textured {
                let (cc, a) = unpremul(src.sample_bilinear(c0[0] as f64, c0[1] as f64));
                if a <= 0.0 {
                    return None;
                }
                pc.flat = Some(cc);
                pc.alpha = a;
            }
            Some(pc)
        })
        .collect();
    if depth_sort {
        sort_far_first(&mut pieces);
    }
    let mut out = Image::new(src.width, src.height);
    draw_pieces(&mut out, &pieces, &src, None);
    b.img = out;
    b
}

// ------------------------------------------------------------------ CC Scatterize

fn scatterize(ctx: &EffectCtx, mut b: Buf) -> Buf {
    let pr = ctx.params;
    let scatter = pr.f("scatter") as f32;
    let right = pr.f("rightTwist").to_radians();
    let left = pr.f("leftTwist").to_radians();
    if scatter == 0.0 && right == 0.0 && left == 0.0 {
        return b;
    }
    let add = pr.e("transferMode") == 1;
    let seed = ctx.seed.wrapping_mul(0x7feb352d);
    let s = b.scale;
    let (w, hh) = (b.img.width, b.img.height);
    let (cx, cy) = (b.offset[0] + ctx.layer_size[0] * 0.5 * s, b.offset[1] + ctx.layer_size[1] * 0.5 * s);
    let half = (ctx.layer_size[0] * 0.5 * s).max(1.0);
    let d = 2.0 * ctx.layer_size[0].max(ctx.layer_size[1]) * s;
    let src = &b.img;
    let sprites: Vec<Sprite> = (0..w * hh)
        .into_par_iter()
        .filter_map(|i| {
            let px = src.data[i as usize];
            if px[3] <= 0.0 {
                return None;
            }
            let (x, y) = ((i % w) as f64 + 0.5, (i / w) as f64 + 0.5);
            // Twist about the horizontal axis through the centre, growing towards each side.
            let k = ((x - cx) / half).abs().min(1.0);
            let ang = if x < cx { left } else { right } * k;
            let (sa, ca) = ang.sin_cos();
            let (yy, zz) = ((y - cy) * ca, (y - cy) * sa);
            let persp = d / (d + zz).max(d * 0.05);
            let jx = hs(i, 1, seed) * scatter * s as f32;
            let jy = hs(i, 2, seed) * scatter * s as f32;
            let sx = cx + (x - cx) * persp + jx as f64;
            let sy = cy + yy * persp + jy as f64;
            let (c, a) = unpremul(px);
            Some(Sprite::new(sx as f32, sy as f32, 0.6 * persp as f32, [c[0], c[1], c[2], a], Shape::Disc))
        })
        .collect();
    b.img = splat(w, hh, &sprites, if add { Acc::Add } else { Acc::Over });
    b
}

// ------------------------------------------------------------------ Card Dance

const CD_SOURCES: &[&str] = &["None", "Intensity 1", "Red 1", "Green 1", "Blue 1", "Alpha 1", "Intensity 2", "Red 2", "Green 2", "Blue 2", "Alpha 2"];
/// (param id prefix, twirl-down group match id) per transformed card property.
const CD_PROPS: [(&str, &str); 8] = [
    ("xPos", "xPosition"),
    ("yPos", "yPosition"),
    ("zPos", "zPosition"),
    ("xRot", "xRotation"),
    ("yRot", "yRotation"),
    ("zRot", "zRotation"),
    ("xScale", "xScale"),
    ("yScale", "yScale"),
];

fn card_source(src: u32, g1: [f32; 4], g2: [f32; 4]) -> f32 {
    let (c1, a1) = unpremul(g1);
    let (c2, a2) = unpremul(g2);
    let lum = |c: [f32; 3]| effectcraft_color::luminance(c[0], c[1], c[2]);
    match src {
        1 => lum(c1),
        2 => c1[0],
        3 => c1[1],
        4 => c1[2],
        5 => a1,
        6 => lum(c2),
        7 => c2[0],
        8 => c2[1],
        9 => c2[2],
        10 => a2,
        _ => 0.0,
    }
}

fn card_dance(ctx: &EffectCtx, mut b: Buf) -> Buf {
    let pr = ctx.params;
    let rows = pr.f("rows").clamp(1.0, 1000.0) as u32;
    let cols = if pr.e("rowsColumns") == 1 { rows } else { pr.f("columns").clamp(1.0, 1000.0) as u32 };
    let g1 = layer_or_self(ctx, &b, "gradientLayer1", true, true);
    let g2 = layer_or_self(ctx, &b, "gradientLayer2", true, true);
    let back = ctx.layer_param("backLayer", true).map(|o| crate::util::fit_layer(ctx, &b, &o, true));
    let [lw, lh] = ctx.layer_size;
    let s = b.scale;
    let (cw, ch) = (lw / cols as f64, lh / rows as f64);
    let zpos = pr.f("cameraPosition/cameraZ").max(0.05);
    let focal = pr.f("cameraPosition/focalLength").max(1.0);
    let cam = Cam { c: [b.offset[0] + lw * 0.5 * s, b.offset[1] + lh * 0.5 * s], d: lw.max(lh) * s * zpos * focal / 140.0 };
    let ambient = pr.f("lighting/ambientLight") as f32;
    let diffuse = pr.f("material/diffuse") as f32;
    let intensity = pr.f("lighting/lightIntensity") as f32;
    let props: Vec<(u32, f64, f64)> =
        CD_PROPS.iter().map(|(id, g)| (pr.e(&format!("{g}/{id}Source")), pr.f(&format!("{g}/{id}Multiplier")), pr.f(&format!("{g}/{id}Offset")))).collect();
    let src = b.img.clone();
    let mut pieces: Vec<Piece> = (0..rows * cols)
        .into_par_iter()
        .filter_map(|i| {
            let (cx0, cy0) = ((i % cols) as f64 * cw, (i / cols) as f64 * ch);
            let c = [cx0 + cw * 0.5, cy0 + ch * 0.5];
            let (bx, by) = (c[0] * s + b.offset[0], c[1] * s + b.offset[1]);
            let (gp1, gp2) = (g1.sample_bilinear(bx, by), g2.sample_bilinear(bx, by));
            let val = |k: usize| {
                let (sr, m, o) = props[k];
                o + m * card_source(sr, gp1, gp2) as f64
            };
            let (sx, sy) = (val(6), val(7));
            let r = rot_xyz(val(3).to_radians(), val(4).to_radians(), val(5).to_radians());
            let rs: M3 = std::array::from_fn(|k| [r[k][0] * sx, r[k][1] * sy, r[k][2]]);
            let pos = [bx + val(0) * cw * s, by + val(1) * ch * s, val(2) * cw.max(ch) * s];
            let (tx0, ty0) = ((cx0 * s + b.offset[0]) as f32, (cy0 * s + b.offset[1]) as f32);
            let (tw, th) = ((cw * s) as f32, (ch * s) as f32);
            let poly = [[tx0, ty0], [tx0 + tw, ty0], [tx0 + tw, ty0 + th], [tx0, ty0 + th]];
            let mut pc = Piece::new(&poly, [bx as f32, by as f32], &rs, pos, cam)?;
            pc.shade = ambient + diffuse * intensity * Piece::facing(&r);
            Some(pc)
        })
        .collect();
    sort_far_first(&mut pieces);
    let mut out = Image::new(src.width, src.height);
    draw_pieces(&mut out, &pieces, &src, back.as_ref());
    b.img = out;
    b
}

// ------------------------------------------------------------------ Shatter

const SHATTER_PATTERNS: &[&str] = &["Bricks", "Glass", "Hexagons", "Squares", "Triangles"];

/// Pattern cells (polygons in pattern space, before rotation) covering `[x0, x1]×[y0, y1]`.
fn pattern_cells(kind: u32, cell: f64, x0: f64, y0: f64, x1: f64, y1: f64, seed: u32) -> Vec<Vec<[f64; 2]>> {
    let mut out = Vec::new();
    let i0 = (x0 / cell).floor() as i64 - 1;
    let i1 = (x1 / cell).ceil() as i64 + 1;
    let j0 = (y0 / cell).floor() as i64 - 1;
    let j1 = (y1 / cell).ceil() as i64 + 1;
    match kind {
        0 => {
            let bh = cell * 0.5;
            let r0 = (y0 / bh).floor() as i64 - 1;
            let r1 = (y1 / bh).ceil() as i64 + 1;
            for r in r0..=r1 {
                let sh = if r.rem_euclid(2) == 1 { cell * 0.5 } else { 0.0 };
                for i in i0..=i1 {
                    let (x, y) = (i as f64 * cell + sh, r as f64 * bh);
                    out.push(vec![[x, y], [x + cell, y], [x + cell, y + bh], [x, y + bh]]);
                }
            }
        }
        1 => {
            // Jittered lattice split into triangles along a random diagonal.
            let jit = |i: i64, j: i64| -> [f64; 2] {
                let (a, b) = (i as u32, j as u32);
                [i as f64 * cell + hs(a, b.wrapping_add(17), seed) as f64 * cell * 0.35, j as f64 * cell + hs(a, b.wrapping_add(91), seed) as f64 * cell * 0.35]
            };
            for j in j0..=j1 {
                for i in i0..=i1 {
                    let (p00, p10, p11, p01) = (jit(i, j), jit(i + 1, j), jit(i + 1, j + 1), jit(i, j + 1));
                    if h(i as u32, j as u32, seed ^ 0x55) < 0.5 {
                        out.push(vec![p00, p10, p11]);
                        out.push(vec![p00, p11, p01]);
                    } else {
                        out.push(vec![p00, p10, p01]);
                        out.push(vec![p10, p11, p01]);
                    }
                }
            }
        }
        2 => {
            let r = cell / 3f64.sqrt();
            let dx = 1.5 * r;
            let dy = 3f64.sqrt() * r;
            let c0 = (x0 / dx).floor() as i64 - 1;
            let c1 = (x1 / dx).ceil() as i64 + 1;
            let rr0 = (y0 / dy).floor() as i64 - 1;
            let rr1 = (y1 / dy).ceil() as i64 + 1;
            for ci in c0..=c1 {
                for rj in rr0..=rr1 {
                    let cx = ci as f64 * dx;
                    let cy = (rj as f64 + if ci.rem_euclid(2) == 1 { 0.5 } else { 0.0 }) * dy;
                    out.push(
                        (0..6)
                            .map(|k| {
                                let a = k as f64 * std::f64::consts::PI / 3.0;
                                [cx + r * a.cos(), cy + r * a.sin()]
                            })
                            .collect(),
                    );
                }
            }
        }
        3 => {
            for j in j0..=j1 {
                for i in i0..=i1 {
                    let (x, y) = (i as f64 * cell, j as f64 * cell);
                    out.push(vec![[x, y], [x + cell, y], [x + cell, y + cell], [x, y + cell]]);
                }
            }
        }
        _ => {
            for j in j0..=j1 {
                for i in i0..=i1 {
                    let (x, y) = (i as f64 * cell, j as f64 * cell);
                    if (i + j).rem_euclid(2) == 0 {
                        out.push(vec![[x, y], [x + cell, y], [x, y + cell]]);
                        out.push(vec![[x + cell, y], [x + cell, y + cell], [x, y + cell]]);
                    } else {
                        out.push(vec![[x, y], [x + cell, y], [x + cell, y + cell]]);
                        out.push(vec![[x, y], [x + cell, y + cell], [x, y + cell]]);
                    }
                }
            }
        }
    }
    out
}

/// `∫0^t e^{-ks} ds` and `∫0^t ∫0^u e^{-ks} ds du` (drag-damped ballistic factors).
fn drag_factors(k: f64, t: f64) -> (f64, f64) {
    if k < 1e-6 {
        (t, 0.5 * t * t)
    } else {
        let e = (-k * t).exp();
        ((1.0 - e) / k, t / k - (1.0 - e) / (k * k))
    }
}

fn shatter(ctx: &EffectCtx, mut b: Buf) -> Buf {
    let pr = ctx.params;
    let view = pr.e("view");
    let render = pr.e("render");
    let kind = pr.e("shape/pattern");
    let reps = pr.f("shape/repetitions").clamp(1.0, 500.0);
    let dir = pr.f("shape/direction").to_radians();
    let origin = pr.v2("shape/origin");
    let forces = [
        (pr.v2("force1/force1Position"), pr.f("force1/force1Depth"), pr.f("force1/force1Radius"), pr.f("force1/force1Strength")),
        (pr.v2("force2/force2Position"), pr.f("force2/force2Depth"), pr.f("force2/force2Radius"), pr.f("force2/force2Strength")),
    ];
    let rot_speed = pr.f("physics/rotationSpeed");
    let tumble = pr.e("physics/tumbleAxis");
    let randomness = pr.f("physics/randomness");
    let k = pr.f("physics/viscosity").max(0.0) * 5.0;
    let mass_var = pr.f("physics/massVariance") / 100.0;
    let gravity = pr.f("physics/gravity");
    let gdir = pr.f("physics/gravityDirection").to_radians();
    let ginc = pr.f("physics/gravityInclination").to_radians();
    let ambient = pr.f("lighting/ambientLight") as f32;
    let intensity = pr.f("lighting/lightIntensity") as f32;
    let seed = (pr.f("randomSeed") as u32).wrapping_mul(0x9e3779b1) ^ ctx.seed;
    let [lw, lh] = ctx.layer_size;
    let s = b.scale;
    let t = ctx.time.max(0.0);
    let unit = lw * 0.1;
    let cell = lw / reps;
    let cam = Cam { c: [b.offset[0] + lw * 0.5 * s, b.offset[1] + lh * 0.5 * s], d: 2.0 * lw.max(lh) * s };
    let (sd, cd) = dir.sin_cos();
    let to_layer = |q: [f64; 2]| [origin[0] + q[0] * cd - q[1] * sd, origin[1] + q[0] * sd + q[1] * cd];
    // Pattern-space bounds of the layer rectangle.
    let corners = [[0.0, 0.0], [lw, 0.0], [lw, lh], [0.0, lh]].map(|c: [f64; 2]| {
        let (dx, dy) = (c[0] - origin[0], c[1] - origin[1]);
        [dx * cd + dy * sd, -dx * sd + dy * cd]
    });
    let (px0, px1) = (corners.iter().map(|c| c[0]).fold(f64::INFINITY, f64::min), corners.iter().map(|c| c[0]).fold(f64::NEG_INFINITY, f64::max));
    let (py0, py1) = (corners.iter().map(|c| c[1]).fold(f64::INFINITY, f64::min), corners.iter().map(|c| c[1]).fold(f64::NEG_INFINITY, f64::max));
    let cells = pattern_cells(kind, cell, px0, py0, px1, py1, seed);
    let g3 = [gdir.sin() * ginc.cos() * gravity * unit, -gdir.cos() * ginc.cos() * gravity * unit, ginc.sin() * gravity * unit];
    let src = b.img.clone();
    let mut pieces: Vec<Piece> = cells
        .par_iter()
        .enumerate()
        .filter_map(|(i, poly)| {
            let i = i as u32;
            let lp: Vec<[f64; 2]> = poly.iter().map(|&q| to_layer(q)).collect();
            let (mnx, mxx) = (lp.iter().map(|v| v[0]).fold(f64::INFINITY, f64::min), lp.iter().map(|v| v[0]).fold(f64::NEG_INFINITY, f64::max));
            let (mny, mxy) = (lp.iter().map(|v| v[1]).fold(f64::INFINITY, f64::min), lp.iter().map(|v| v[1]).fold(f64::NEG_INFINITY, f64::max));
            if mxx < 0.0 || mxy < 0.0 || mnx > lw || mny > lh {
                return None;
            }
            let c = [lp.iter().map(|v| v[0]).sum::<f64>() / lp.len() as f64, lp.iter().map(|v| v[1]).sum::<f64>() / lp.len() as f64];
            // Broken when inside a force sphere (centred `depth` in front of the layer).
            let mut v = [0.0f64; 3];
            let mut broken = false;
            for (fp, fd, fr, fs) in forces {
                let rad = fr * lw;
                if rad <= 0.0 {
                    continue;
                }
                let dv = [c[0] - fp[0], c[1] - fp[1], fd * lw];
                let dist = (dv[0] * dv[0] + dv[1] * dv[1] + dv[2] * dv[2]).sqrt();
                if dist < rad {
                    broken = true;
                    let f = fs * (1.0 - dist / rad) * unit / dist.max(1e-6);
                    for q in 0..3 {
                        v[q] += dv[q] * f;
                    }
                }
            }
            if (broken && render == 1) || (!broken && render == 2) {
                return None;
            }
            let mut pos = [c[0], c[1], 0.0];
            let mut r = rot_axis([1.0, 0.0, 0.0], 0.0);
            if broken && t > 0.0 {
                let mass = 1.0 + mass_var * hs(i, 1, seed) as f64;
                for q in 0..3 {
                    v[q] = v[q] / mass + randomness * unit * hs(i, 2 + q as u32, seed) as f64 * 2.0;
                }
                let (f1, f2) = drag_factors(k, t);
                for q in 0..3 {
                    pos[q] += v[q] * f1 + g3[q] * f2;
                }
                let axis = match tumble {
                    1 => [0.0, 0.0, 0.0],
                    2 => [1.0, 0.0, 0.0],
                    3 => [0.0, 1.0, 0.0],
                    4 => [0.0, 0.0, 1.0],
                    5 => [hs(i, 6, seed) as f64, hs(i, 7, seed) as f64, 0.0],
                    6 => [hs(i, 6, seed) as f64, 0.0, hs(i, 8, seed) as f64],
                    7 => [0.0, hs(i, 7, seed) as f64, hs(i, 8, seed) as f64],
                    _ => [hs(i, 6, seed) as f64, hs(i, 7, seed) as f64, hs(i, 8, seed) as f64],
                };
                let speed = (v[0] * v[0] + v[1] * v[1] + v[2] * v[2]).sqrt() / unit;
                let omega = rot_speed * std::f64::consts::TAU * (0.5 + h(i, 9, seed) as f64) * speed.min(10.0);
                r = rot_axis(axis, omega * f1);
            }
            let tex: Vec<[f32; 2]> = lp.iter().map(|v| [(v[0] * s + b.offset[0]) as f32, (v[1] * s + b.offset[1]) as f32]).collect();
            let c0 = [(c[0] * s + b.offset[0]) as f32, (c[1] * s + b.offset[1]) as f32];
            let posb = [pos[0] * s + b.offset[0], pos[1] * s + b.offset[1], pos[2] * s];
            let mut pc = Piece::new(&tex, c0, &r, posb, cam)?;
            pc.shade = ambient + (1.0 - ambient) * intensity * Piece::facing(&r);
            Some(pc)
        })
        .collect();
    sort_far_first(&mut pieces);
    let mut out = Image::new(src.width, src.height);
    if view == 0 {
        draw_pieces(&mut out, &pieces, &src, None);
    } else {
        // Wireframes: piece outlines (front view: at rest; otherwise animated), plus forces.
        let animated = view == 2 || view == 4;
        let mut lines = Vec::new();
        for pc in &pieces {
            let n = pc.n as usize;
            let pts: Vec<[f32; 2]> = if animated {
                let fw = inv3(&pc.inv);
                match fw {
                    Some(m) => pc.poly[..n]
                        .iter()
                        .map(|v| {
                            let (a, bb) = ((v[0] - pc.c0[0]) as f64, (v[1] - pc.c0[1]) as f64);
                            let w = m[2][0] * a + m[2][1] * bb + m[2][2];
                            [((m[0][0] * a + m[0][1] * bb + m[0][2]) / w) as f32, ((m[1][0] * a + m[1][1] * bb + m[1][2]) / w) as f32]
                        })
                        .collect(),
                    None => continue,
                }
            } else {
                pc.poly[..n].to_vec()
            };
            for e in 0..n {
                let (a, c) = (pts[e], pts[(e + 1) % n]);
                lines.push(Sprite::new(a[0], a[1], 0.5, [0.75, 0.85, 1.0, 1.0], Shape::Line { dx: c[0] - a[0], dy: c[1] - a[1] }));
            }
        }
        if view >= 3 {
            for (fp, _, fr, _) in forces {
                let (fx, fy) = b.to_px(fp);
                let rad = fr * lw * s;
                for k in 0..64 {
                    let (a0, a1) = (k as f64 / 64.0 * std::f64::consts::TAU, (k + 1) as f64 / 64.0 * std::f64::consts::TAU);
                    let (x0, y0) = (fx + rad * a0.cos(), fy + rad * a0.sin());
                    let (x1, y1) = (fx + rad * a1.cos(), fy + rad * a1.sin());
                    lines.push(Sprite::new(x0 as f32, y0 as f32, 0.5, [1.0, 0.3, 0.3, 1.0], Shape::Line { dx: (x1 - x0) as f32, dy: (y1 - y0) as f32 }));
                }
            }
        }
        out = splat(src.width, src.height, &lines, Acc::Over);
    }
    b.img = out;
    b
}

// ------------------------------------------------------------------ Caustics

/// Sample with repeat mode: 0 Once (transparent outside), 1 Tiled, 2 Reflected.
fn sample_repeat(img: &Image, x: f64, y: f64, mode: u32) -> Px {
    let (w, hh) = (img.width as f64, img.height as f64);
    match mode {
        1 => img.sample_bilinear_clamped(x.rem_euclid(w), y.rem_euclid(hh)),
        2 => {
            let m = |v: f64, n: f64| {
                let r = v.rem_euclid(2.0 * n);
                if r > n { 2.0 * n - r } else { r }
            };
            img.sample_bilinear_clamped(m(x, w), m(y, hh))
        }
        _ => img.sample_bilinear(x, y),
    }
}

fn caustics(ctx: &EffectCtx, mut b: Buf) -> Buf {
    let pr = ctx.params;
    let s = b.scale;
    let mut bottom = layer_or_self(ctx, &b, "bottom/bottom", true, pr.e("bottom/bottomSizeDiffers") == 1);
    let blur = pr.f("bottom/blur") * s;
    if blur > 0.05 {
        bottom = effectcraft_raster::gaussian_blur(&bottom, blur * 0.5, blur * 0.5, false);
    }
    let scaling = pr.f("bottom/scaling").max(0.01);
    let repeat = pr.e("bottom/repeatMode");
    let wave_h = pr.f("water/waveHeight");
    let smoothing = pr.f("water/smoothing") * s;
    let depth = pr.f("water/waterDepth");
    let ior = pr.f("water/refractiveIndex").max(1.0);
    let surf = pr.color("water/surfaceColor");
    let surf_op = pr.f("water/surfaceOpacity") as f32;
    let cstr = pr.f("water/causticsStrength") as f32;
    let li = pr.f("lighting/lightIntensity") as f32;
    let lc = pr.color("lighting/lightColor");
    let lpos = pr.v2("lighting/lightPosition");
    let lheight = pr.f("lighting/lightHeight").max(0.01);
    let ambient = pr.f("lighting/ambientLight") as f32;
    let diffuse = pr.f("material/diffuse") as f32;
    let specular = pr.f("material/specular") as f32;
    let sharp = pr.f("material/highlightSharpness").max(1.0) as f32;
    let (w, hh) = (b.img.width as usize, b.img.height as usize);
    // Height field of the water surface (luminance of the chosen layer; none = flat).
    let height = ctx.layer_param("water/waterSurface", true).map(|o| {
        let img = crate::util::fit_layer(ctx, &b, &o, true);
        let pl = Plane::luma(&img);
        if smoothing > 0.05 { gauss_plane(&pl, smoothing * 0.5, smoothing * 0.5) } else { pl }
    });
    let lw = ctx.layer_size[0] * s;
    let k = wave_h * depth * (1.0 - 1.0 / ior) * lw * 2.0;
    let (cx, cy) = (b.offset[0] + ctx.layer_size[0] * 0.5 * s, b.offset[1] + ctx.layer_size[1] * 0.5 * s);
    let (lx, ly) = b.to_px(lpos);
    let lv = {
        let v = [(lx - cx) / lw.max(1.0), (ly - cy) / lw.max(1.0), lheight];
        let n = (v[0] * v[0] + v[1] * v[1] + v[2] * v[2]).sqrt();
        [(v[0] / n) as f32, (v[1] / n) as f32, (v[2] / n) as f32]
    };
    let grad = |x: usize, y: usize| -> (f64, f64) {
        match &height {
            Some(pl) => {
                let gx = (pl.get_clamped(x as i64 + 1, y as i64) - pl.get_clamped(x as i64 - 1, y as i64)) as f64 * 0.5;
                let gy = (pl.get_clamped(x as i64, y as i64 + 1) - pl.get_clamped(x as i64, y as i64 - 1)) as f64 * 0.5;
                (gx, gy)
            }
            None => (0.0, 0.0),
        }
    };
    // Displacement and its Jacobian (caustic focusing) per pixel.
    let disp: Vec<(f64, f64)> = (0..w * hh)
        .into_par_iter()
        .map(|i| {
            let (gx, gy) = grad(i % w, i / w);
            (-gx * k, -gy * k)
        })
        .collect();
    b.img.rows_mut().for_each(|(y, row)| {
        for (x, px) in row.iter_mut().enumerate() {
            let i = y * w + x;
            let (dx, dy) = disp[i];
            let d = |xx: usize, yy: usize| disp[yy.min(hh - 1) * w + xx.min(w - 1)];
            let (dxr, _) = d(x + 1, y);
            let (_, dyd) = d(x, y + 1);
            let (dxl, _) = d(x.saturating_sub(1), y);
            let (_, dyu) = d(x, y.saturating_sub(1));
            let jac = (1.0 + (dxr - dxl) * 0.5) * (1.0 + (dyd - dyu) * 0.5);
            let focus = ((1.0 / jac.abs().max(0.2)) as f32 - 1.0).clamp(-1.0, 4.0);
            let sx = cx + (x as f64 + 0.5 + dx - cx) / scaling;
            let sy = cy + (y as f64 + 0.5 + dy - cy) / scaling;
            let p = sample_repeat(&bottom, sx, sy, repeat);
            let (c, a) = unpremul(p);
            let (gx, gy) = grad(x, y);
            let n = {
                let v = [-gx * wave_h * 20.0, -gy * wave_h * 20.0, 1.0];
                let m = (v[0] * v[0] + v[1] * v[1] + 1.0).sqrt();
                [(v[0] / m) as f32, (v[1] / m) as f32, (v[2] / m) as f32]
            };
            let nl = (n[0] * lv[0] + n[1] * lv[1] + n[2] * lv[2]).max(0.0);
            let hv = {
                let v = [lv[0], lv[1], lv[2] + 1.0];
                let m = (v[0] * v[0] + v[1] * v[1] + v[2] * v[2]).sqrt();
                [v[0] / m, v[1] / m, v[2] / m]
            };
            let spec = (n[0] * hv[0] + n[1] * hv[1] + n[2] * hv[2]).max(0.0).powf(sharp) * specular * li;
            let light = ambient + diffuse * li * nl + cstr * focus * li;
            let cc: [f32; 3] = std::array::from_fn(|q| {
                let base = c[q] * light * lc[q];
                base * (1.0 - surf_op) + surf[q] * surf_op * (ambient + diffuse * li * nl) + spec * lc[q]
            });
            let a = (a + surf_op * (1.0 - a)).min(1.0);
            *px = [cc[0] * a, cc[1] * a, cc[2] * a, a];
        }
    });
    b
}

// ------------------------------------------------------------------ Wave World

#[derive(Clone, Debug)]
struct Waves {
    nx: usize,
    ny: usize,
    u: Vec<f32>,
    v: Vec<f32>,
}

struct Producer {
    ring: bool,
    pos: [f32; 2],
    len: f32,
    width: f32,
    angle: f32,
    amp: f32,
    freq: f32,
    phase: f32,
}

impl Producer {
    /// Weight of a grid point (layer-fraction coordinates, x in widths, y in widths).
    fn weight(&self, x: f32, y: f32) -> f32 {
        let (dx, dy) = (x - self.pos[0], y - self.pos[1]);
        let (sa, ca) = self.angle.sin_cos();
        let (u, v) = (dx * ca + dy * sa, -dx * sa + dy * ca);
        let d = if self.ring {
            let (a, bb) = ((self.len * 0.5).max(1e-3), (self.width * 0.5).max(1e-3));
            ((u / a).powi(2) + (v / bb).powi(2)).sqrt()
        } else {
            let l = (self.len * 0.5).max(1e-3);
            let wd = (self.width * 0.5).max(1e-3);
            (u.abs() / l).max(v.abs() / wd)
        };
        (1.0 - d).clamp(0.0, 1.0).min(1.0)
    }
}

static WAVE_CACHE: SimCache<Waves> = SimCache::new(4);

fn wave_world(ctx: &EffectCtx, mut b: Buf) -> Buf {
    let pr = ctx.params;
    let [lw, lh] = ctx.layer_size;
    let res = pr.f("simulation/gridResolution").clamp(1.0, 400.0) as usize;
    let res = if pr.b("simulation/gridResDownsamples") { ((res as f64) * b.scale).round().max(1.0) as usize } else { res };
    let nx = res.max(2) + 1;
    let ny = ((res as f64 * lh / lw.max(1.0)).round() as usize).max(2) + 1;
    let speed = pr.f("simulation/waveSpeed").max(0.0) as f32;
    let damping = pr.f("simulation/damping").max(0.0) as f32;
    let reflect = pr.e("simulation/reflectEdges");
    let preroll = pr.f("simulation/preRoll").max(0.0);
    let prods: Vec<Producer> = [1, 2]
        .iter()
        .map(|k| {
            let pos = pr.v2(&format!("producer{k}/producer{k}Position"));
            Producer {
                ring: pr.e(&format!("producer{k}/producer{k}Type")) == 0,
                pos: [(pos[0] / lw.max(1.0)) as f32, (pos[1] / lw.max(1.0)) as f32],
                len: pr.f(&format!("producer{k}/producer{k}Length")) as f32,
                width: pr.f(&format!("producer{k}/producer{k}Width")) as f32,
                angle: (pr.f(&format!("producer{k}/producer{k}Angle")) as f32).to_radians(),
                amp: pr.f(&format!("producer{k}/producer{k}Amplitude")) as f32,
                freq: pr.f(&format!("producer{k}/producer{k}Frequency")) as f32,
                phase: (pr.f(&format!("producer{k}/producer{k}Phase")) as f32).to_radians(),
            }
        })
        .collect();
    let sps = crate::sim::SPS as f32;
    // Wave speed in layer widths per second → cells per second; sub-steps keep it stable.
    let cps = speed * (nx - 1) as f32;
    let sub = ((cps * 2.0 / sps).ceil() as usize).clamp(1, 64);
    let dt = 1.0 / (sps * sub as f32);
    let cell = 1.0 / (nx - 1) as f32;
    let weights: Vec<Vec<f32>> = prods.iter().map(|p| (0..nx * ny).map(|i| p.weight((i % nx) as f32 * cell, (i / nx) as f32 * cell)).collect()).collect();
    let key = params_key(ctx, &Buf { img: Image::new(0, 0), offset: [0.0; 2], scale: if pr.b("simulation/gridResDownsamples") { b.scale } else { 1.0 } }, 4);
    let steps = crate::sim::steps_at(ctx.time + preroll);
    let st = WAVE_CACHE.run(
        key,
        steps,
        || Waves { nx, ny, u: vec![0.0; nx * ny], v: vec![0.0; nx * ny] },
        |w, step| {
            for k in 0..sub {
                let t = (step as f32 + k as f32 / sub as f32) / sps - preroll as f32;
                let c2 = cps * cps;
                let mut acc = vec![0.0f32; nx * ny];
                for y in 0..ny {
                    for x in 0..nx {
                        let i = y * nx + x;
                        let g = |xx: usize, yy: usize| w.u[yy * nx + xx];
                        let l = g(x.saturating_sub(1), y) + g((x + 1).min(nx - 1), y) + g(x, y.saturating_sub(1)) + g(x, (y + 1).min(ny - 1)) - 4.0 * w.u[i];
                        acc[i] = c2 * l - damping * 4.0 * w.v[i];
                    }
                }
                for i in 0..nx * ny {
                    w.v[i] += acc[i] * dt;
                    w.u[i] += w.v[i] * dt;
                }
                // Producers drive the surface.
                for (p, wt) in prods.iter().zip(&weights) {
                    if p.amp == 0.0 {
                        continue;
                    }
                    let target = p.amp * (std::f32::consts::TAU * p.freq * t + p.phase).sin();
                    for i in 0..nx * ny {
                        if wt[i] > 0.0 {
                            w.u[i] += (target - w.u[i]) * wt[i];
                            w.v[i] *= 1.0 - wt[i];
                        }
                    }
                }
                // Edges: reflective ones mirror; the others absorb in a thin sponge layer.
                let refl = |side: u32| reflect == 5 || reflect == side;
                let sponge = 4usize.min(nx / 4).max(1);
                for y in 0..ny {
                    for x in 0..nx {
                        let i = y * nx + x;
                        let mut f = 1.0f32;
                        if !refl(1) && x < sponge {
                            f = f.min(x as f32 / sponge as f32);
                        }
                        if !refl(3) && nx - 1 - x < sponge {
                            f = f.min((nx - 1 - x) as f32 / sponge as f32);
                        }
                        if !refl(2) && y < sponge {
                            f = f.min(y as f32 / sponge as f32);
                        }
                        if !refl(4) && ny - 1 - y < sponge {
                            f = f.min((ny - 1 - y) as f32 / sponge as f32);
                        }
                        if f < 1.0 {
                            let k = 0.85 + 0.15 * f;
                            w.u[i] *= k;
                            w.v[i] *= k;
                        }
                    }
                }
            }
        },
    );
    let s = b.scale;
    let (bw, bh) = (b.img.width, b.img.height);
    let sample = |x: f64, y: f64| -> f32 {
        let gx = (x / lw.max(1.0) * (st.nx - 1) as f64).clamp(0.0, (st.nx - 1) as f64);
        let gy = (y / lw.max(1.0) * (st.nx - 1) as f64).clamp(0.0, (st.ny - 1) as f64);
        let (x0, y0) = (gx.floor() as usize, gy.floor() as usize);
        let (x1, y1) = ((x0 + 1).min(st.nx - 1), (y0 + 1).min(st.ny - 1));
        let (tx, ty) = ((gx - x0 as f64) as f32, (gy - y0 as f64) as f32);
        let g = |xx: usize, yy: usize| st.u[yy * st.nx + xx];
        let a = g(x0, y0) + (g(x1, y0) - g(x0, y0)) * tx;
        let c = g(x0, y1) + (g(x1, y1) - g(x0, y1)) * tx;
        a + (c - a) * ty
    };
    if pr.e("view") == 1 {
        let bright = pr.f("heightMapControls/brightness") as f32;
        let contrast = pr.f("heightMapControls/contrast") as f32;
        let gamma = pr.f("heightMapControls/gamma").max(0.01) as f32;
        let alpha = 1.0 - pr.f("heightMapControls/transparency") as f32;
        b.img.rows_mut().for_each(|(y, row)| {
            for (x, px) in row.iter_mut().enumerate() {
                let lx = (x as f64 + 0.5 - b.offset[0]) / s;
                let ly = (y as f64 + 0.5 - b.offset[1]) / s;
                let v = (bright + contrast * sample(lx, ly)).clamp(0.0, 1.0).powf(1.0 / gamma);
                *px = [v * alpha, v * alpha, v * alpha, alpha];
            }
        });
    } else {
        // Wireframe preview: the grid seen at an angle, heights lifting the lines.
        let lift = lh as f32 * 0.25;
        let to = |x: usize, y: usize| -> [f32; 2] {
            let lx = x as f64 / (st.nx - 1) as f64 * lw;
            let ly = y as f64 / (st.nx - 1) as f64 * lw;
            let (px, py) = b.to_px([lx, lh * 0.25 + ly * 0.6]);
            [px as f32, py as f32 - st.u[y * st.nx + x] * lift * s as f32]
        };
        let mut lines = Vec::new();
        for y in 0..st.ny {
            for x in 0..st.nx {
                let a = to(x, y);
                if x + 1 < st.nx {
                    let c = to(x + 1, y);
                    lines.push(Sprite::new(a[0], a[1], 0.4, [0.4, 0.9, 0.4, 1.0], Shape::Line { dx: c[0] - a[0], dy: c[1] - a[1] }));
                }
                if y + 1 < st.ny {
                    let c = to(x, y + 1);
                    lines.push(Sprite::new(a[0], a[1], 0.4, [0.4, 0.9, 0.4, 1.0], Shape::Line { dx: c[0] - a[0], dy: c[1] - a[1] }));
                }
            }
        }
        let wire = splat(bw, bh, &lines, Acc::Over);
        b.img = crate::sim::combine(&Image::filled(bw, bh, [0.0, 0.0, 0.0, 1.0]), &wire, 0);
    }
    b
}

// ------------------------------------------------------------------ Foam

#[derive(Clone, Debug)]
struct FoamBubble {
    p: [f32; 2],
    v: [f32; 2],
    age: f32,
    size: f32,
    id: u32,
}

#[derive(Clone, Debug, Default)]
struct FoamState {
    b: Vec<FoamBubble>,
    carry: f32,
    next: u32,
}

static FOAM_CACHE: SimCache<FoamState> = SimCache::new(4);

/// Foam steps once per frame at 30 frames per second.
const FOAM_FPS: f64 = 30.0;

/// Age (in simulation steps) at which bubble `id` pops: its lifespan, shortened at random for
/// frail bubbles (`frailty` 0 = every bubble reaches `lifespan`, 1 = uniformly early).
fn foam_pop_age(id: u32, lifespan: f32, frailty: f32, seed: u32) -> f32 {
    lifespan * (1.0 - frailty * (hs(id, 11, seed) * 0.5 + 0.5))
}

fn foam(ctx: &EffectCtx, mut b: Buf) -> Buf {
    let pr = ctx.params;
    let (lw, lh) = (ctx.layer_size[0] as f32, ctx.layer_size[1] as f32);
    let unit = lw * 0.01;
    let prod = pr.v2("producer/producerPoint");
    let (psx, psy) = (pr.f("producer/producerXSize") as f32 * lw, pr.f("producer/producerYSize") as f32 * lh);
    let porient = (pr.f("producer/producerOrientation") as f32).to_radians();
    let rate = pr.f("producer/productionRate").max(0.0) as f32;
    let size = pr.f("bubbles/size").max(0.0) as f32;
    let size_var = pr.f("bubbles/sizeVariance") as f32;
    let lifespan = pr.f("bubbles/lifespan").max(1.0) as f32;
    let growth = pr.f("bubbles/growthSpeed").max(0.0001) as f32;
    // Strength: weaker bubbles tend to pop before their lifespan (at 20 or more every bubble
    // lives the full lifespan); each bubble gets its own pop age.
    let frailty = 1.0 - (pr.f("bubbles/strength") as f32 / 20.0).clamp(0.0, 1.0);
    let init_speed = pr.f("physics/initialSpeed") as f32;
    let init_dir = (pr.f("physics/initialDirection") as f32).to_radians();
    let wind = pr.f("physics/windSpeed") as f32;
    let wind_dir = (pr.f("physics/windDirection") as f32).to_radians();
    let turb = pr.f("physics/turbulence") as f32;
    let repulsion = pr.f("physics/repulsion") as f32;
    let viscosity = pr.f("physics/viscosity").clamp(0.0, 1.0) as f32;
    let sticky = pr.f("physics/stickiness").clamp(0.0, 1.0) as f32;
    let universe = pr.f("universeSize").max(0.01) as f32;
    let seed = (pr.f("randomSeed") as u32).wrapping_mul(0x68e31da4) ^ ctx.seed;
    let wvec = [wind_dir.sin() * wind * unit, -wind_dir.cos() * wind * unit];
    let key = params_key(ctx, &Buf { img: Image::new(0, 0), offset: [0.0; 2], scale: 1.0 }, 5);
    let steps = if ctx.time <= 0.0 { 0 } else { (ctx.time * FOAM_FPS + 1e-6).floor() as u64 };
    let st = FOAM_CACHE.run(key, steps, FoamState::default, |st, step| {
        let t = step as f32 / FOAM_FPS as f32;
        // Births.
        st.carry += rate;
        let n = st.carry.floor() as u32;
        st.carry -= n as f32;
        for _ in 0..n {
            if st.b.len() >= 3000 {
                break;
            }
            let id = st.next;
            st.next = st.next.wrapping_add(1);
            let (ux, uy) = (hs(id, 1, seed) * 0.5 * psx, hs(id, 2, seed) * 0.5 * psy);
            let (so, co) = porient.sin_cos();
            let p = [prod[0] as f32 + ux * co - uy * so, prod[1] as f32 + ux * so + uy * co];
            let v = [init_dir.sin() * init_speed * unit, -init_dir.cos() * init_speed * unit];
            let sz = (size * (1.0 + size_var * hs(id, 3, seed))).max(0.01);
            st.b.push(FoamBubble { p, v, age: 0.0, size: sz, id });
        }
        // Forces: drift towards the wind, turbulence, viscosity.
        for q in st.b.iter_mut() {
            let n1 = value_noise(q.p[0] / (lw * 0.15), q.p[1] / (lw * 0.15), t * 0.5, seed) - 0.5;
            let n2 = value_noise(q.p[0] / (lw * 0.15) + 19.0, q.p[1] / (lw * 0.15), t * 0.5, seed) - 0.5;
            for k in 0..2 {
                q.v[k] += (wvec[k] - q.v[k]) * 0.1;
                q.v[k] *= 1.0 - viscosity * 0.5;
            }
            q.v[0] += n1 * turb * unit;
            q.v[1] += n2 * turb * unit;
        }
        // Repulsion between overlapping bubbles (grid hashed, deterministic order).
        let rad = |q: &FoamBubble| q.size * unit * 3.0 * (q.age * growth).min(1.0);
        if repulsion > 0.0 && st.b.len() > 1 {
            let maxr = st.b.iter().map(rad).fold(0.0f32, f32::max).max(1.0);
            let cs = maxr * 2.0;
            let mut grid: std::collections::HashMap<(i32, i32), Vec<usize>> = std::collections::HashMap::new();
            for (i, q) in st.b.iter().enumerate() {
                grid.entry(((q.p[0] / cs).floor() as i32, (q.p[1] / cs).floor() as i32)).or_default().push(i);
            }
            let mut push = vec![[0.0f32; 2]; st.b.len()];
            for (i, q) in st.b.iter().enumerate() {
                let (gx, gy) = ((q.p[0] / cs).floor() as i32, (q.p[1] / cs).floor() as i32);
                for dy in -1..=1 {
                    for dx in -1..=1 {
                        let Some(list) = grid.get(&(gx + dx, gy + dy)) else { continue };
                        for &j in list {
                            if j <= i {
                                continue;
                            }
                            let o = &st.b[j];
                            let (ddx, ddy) = (o.p[0] - q.p[0], o.p[1] - q.p[1]);
                            let d = (ddx * ddx + ddy * ddy).sqrt().max(1e-4);
                            let overlap = rad(q) + rad(o) - d;
                            if overlap > 0.0 {
                                let f = overlap * 0.5 * repulsion.min(4.0) * (1.0 - sticky * 0.5) / d;
                                push[i][0] -= ddx * f;
                                push[i][1] -= ddy * f;
                                push[j][0] += ddx * f;
                                push[j][1] += ddy * f;
                            }
                        }
                    }
                }
            }
            for (q, d) in st.b.iter_mut().zip(&push) {
                q.p[0] += d[0].clamp(-maxr, maxr);
                q.p[1] += d[1].clamp(-maxr, maxr);
            }
        }
        let (ux0, uy0) = (-(universe - 1.0) * 0.5 * lw, -(universe - 1.0) * 0.5 * lh);
        let (ux1, uy1) = (lw - ux0, lh - uy0);
        for q in st.b.iter_mut() {
            q.p[0] += q.v[0];
            q.p[1] += q.v[1];
            q.age += 1.0;
        }
        st.b.retain(|q| q.age < foam_pop_age(q.id, lifespan, frailty, seed) && q.p[0] > ux0 && q.p[0] < ux1 && q.p[1] > uy0 && q.p[1] < uy1);
    });
    let view = pr.e("view");
    let zoom = pr.f("zoom").max(0.01) as f32;
    let texture = pr.e("rendering/bubbleTexture");
    let blend = pr.e("rendering/blendMode");
    let s = b.scale as f32;
    let (cx, cy) = (lw * 0.5, lh * 0.5);
    let mut order: Vec<&FoamBubble> = st.b.iter().collect();
    if blend == 2 {
        // Solid New on Top: oldest first.
        order.sort_by(|a, c| c.age.total_cmp(&a.age).then(a.id.cmp(&c.id)));
    } else if blend == 1 {
        order.sort_by(|a, c| a.age.total_cmp(&c.age).then(a.id.cmp(&c.id)));
    }
    let sprites: Vec<Sprite> = order
        .iter()
        .map(|q| {
            let r = q.size * unit * 3.0 * (q.age * growth).min(1.0) * zoom * s;
            let (bx, by) = b.to_px([(cx + (q.p[0] - cx) * zoom) as f64, (cy + (q.p[1] - cy) * zoom) as f64]);
            let fade = ((foam_pop_age(q.id, lifespan, frailty, seed) - q.age) / 5.0).clamp(0.0, 1.0);
            // Draft and Draft + Flow Map show the wireframe-style bubbles.
            if view != 2 {
                Sprite::new(bx as f32, by as f32, r, [0.55, 0.75, 1.0, fade], Shape::Bubble)
            } else {
                let (c, shape) = match texture {
                    1 => ([0.95, 0.95, 0.92], Shape::Faded),
                    2 => ([1.0, 0.6, 0.8], Shape::Bubble),
                    3 => ([0.8, 0.85, 0.75], Shape::Bubble),
                    4 => ([0.97, 0.97, 0.95], Shape::Sphere),
                    _ => ([1.0, 1.0, 1.0], Shape::Bubble),
                };
                Sprite::new(bx as f32, by as f32, r, [c[0], c[1], c[2], fade], shape)
            }
        })
        .collect();
    b.img = splat(b.img.width, b.img.height, &sprites, if blend == 0 && view == 2 { Acc::Add } else { Acc::Over });
    b
}

// ------------------------------------------------------------------ specs

fn producer_params(k: u32, amp: f64, pos: (f64, f64)) -> Vec<crate::ParamSpec> {
    let ids: [&'static str; 8] = match k {
        1 => [
            "producer1/producer1Type",
            "producer1/producer1Position",
            "producer1/producer1Length",
            "producer1/producer1Width",
            "producer1/producer1Angle",
            "producer1/producer1Amplitude",
            "producer1/producer1Frequency",
            "producer1/producer1Phase",
        ],
        _ => [
            "producer2/producer2Type",
            "producer2/producer2Position",
            "producer2/producer2Length",
            "producer2/producer2Width",
            "producer2/producer2Angle",
            "producer2/producer2Amplitude",
            "producer2/producer2Frequency",
            "producer2/producer2Phase",
        ],
    };
    vec![
        p(ids[0], "Type", Value::Enum(0), popup(&["Ring", "Line"])),
        p(ids[1], "Position", pt(pos.0, pos.1), ParamUi::Point),
        p(ids[2], "Height/Length", num(0.1), slider(0.0, 2.0, 0.0, 1.0, 3)),
        p(ids[3], "Width", num(0.1), slider(0.0, 2.0, 0.0, 1.0, 3)),
        p(ids[4], "Angle", num(0.0), ParamUi::Angle),
        p(ids[5], "Amplitude", num(amp), slider(-5.0, 5.0, -1.0, 1.0, 3)),
        p(ids[6], "Frequency", num(1.0), slider(0.0, 30.0, 0.0, 5.0, 3)),
        p(ids[7], "Phase", num(0.0), ParamUi::Angle),
    ]
}

fn card_dance_params() -> Vec<crate::ParamSpec> {
    let mut v = vec![
        p("rowsColumns", "Rows & Columns", Value::Enum(0), popup(&["Independent", "Columns Follows Rows"])),
        p("rows", "Rows", num(10.0), slider(1.0, 1000.0, 1.0, 100.0, 0)),
        p("columns", "Columns", num(10.0), slider(1.0, 1000.0, 1.0, 100.0, 0)),
        p("backLayer", "Back Layer", Value::Layer(None), ParamUi::Layer),
        p("gradientLayer1", "Gradient Layer 1", Value::Layer(None), ParamUi::Layer),
        p("gradientLayer2", "Gradient Layer 2", Value::Layer(None), ParamUi::Layer),
    ];
    let names: [[&'static str; 4]; 8] = [
        ["xPosition/xPosSource", "xPosition/xPosMultiplier", "xPosition/xPosOffset", "X Position"],
        ["yPosition/yPosSource", "yPosition/yPosMultiplier", "yPosition/yPosOffset", "Y Position"],
        ["zPosition/zPosSource", "zPosition/zPosMultiplier", "zPosition/zPosOffset", "Z Position"],
        ["xRotation/xRotSource", "xRotation/xRotMultiplier", "xRotation/xRotOffset", "X Rotation"],
        ["yRotation/yRotSource", "yRotation/yRotMultiplier", "yRotation/yRotOffset", "Y Rotation"],
        ["zRotation/zRotSource", "zRotation/zRotMultiplier", "zRotation/zRotOffset", "Z Rotation"],
        ["xScale/xScaleSource", "xScale/xScaleMultiplier", "xScale/xScaleOffset", "X Scale"],
        ["yScale/yScaleSource", "yScale/yScaleMultiplier", "yScale/yScaleOffset", "Y Scale"],
    ];
    debug_assert_eq!(names.len(), CD_PROPS.len());
    for (i, n) in names.iter().enumerate() {
        let rot = (3..6).contains(&i);
        let scale = i >= 6;
        let (lo, hi) = if rot { (-3600.0, 3600.0) } else { (-100.0, 100.0) };
        v.push(p(n[0], "Source", Value::Enum(0), popup(CD_SOURCES)));
        v.push(p(n[1], "Multiplier", num(0.0), slider(lo, hi, if rot { -360.0 } else { -10.0 }, if rot { 360.0 } else { 10.0 }, 2)));
        v.push(p(n[2], "Offset", num(if scale { 1.0 } else { 0.0 }), slider(lo, hi, if rot { -360.0 } else { -10.0 }, if rot { 360.0 } else { 10.0 }, 2)));
    }
    v.extend([
        p("cameraPosition/cameraZ", "Z Position", num(2.0), slider(0.05, 10.0, 0.5, 5.0, 2)),
        p("cameraPosition/focalLength", "Focal Length", num(70.0), slider(1.0, 500.0, 10.0, 200.0, 1)),
        p("lighting/lightIntensity", "Light Intensity", num(1.0), slider(0.0, 4.0, 0.0, 2.0, 2)),
        p("lighting/ambientLight", "Ambient Light", num(0.25), slider(0.0, 2.0, 0.0, 1.0, 2)),
        p("material/diffuse", "Diffuse Reflection", num(0.75), slider(0.0, 2.0, 0.0, 1.0, 2)),
    ]);
    v
}

pub fn specs() -> Vec<EffectSpec> {
    vec![
        spec(
            "ec.sim.ccballaction",
            "CC Ball Action",
            vec![
                p("scatter", "Scatter", num(0.0), slider(0.0, 2000.0, 0.0, 300.0, 1)),
                p("rotationAxis", "Rotation Axis", Value::Enum(0), popup(&["X Axis", "Y Axis", "Z Axis", "XY Axis", "XZ Axis", "YZ Axis", "XYZ Axis"])),
                p("rotation", "Rotation", num(0.0), ParamUi::Angle),
                p("twistProperty", "Twist Property", Value::Enum(0), popup(&["X Axis", "Y Axis", "Radius", "Brightness"])),
                p("twistAngle", "Twist Angle", num(0.0), ParamUi::Angle),
                p("gridSpacing", "Grid Spacing", num(4.0), slider(1.0, 200.0, 1.0, 50.0, 0)),
                p("ballSize", "Ball Size", num(40.0), slider(0.0, 400.0, 0.0, 200.0, 1)),
                p("instabilityState", "Instability State", num(0.0), ParamUi::Angle),
            ],
            ball_action,
        ),
        spec(
            "ec.sim.ccpixelpolly",
            "CC Pixel Polly",
            vec![
                p("force", "Force", num(100.0), slider(-1000.0, 1000.0, -300.0, 300.0, 1)),
                p("gravity", "Gravity", num(1.0), slider(-20.0, 20.0, -5.0, 5.0, 2)),
                p("spinning", "Spinning", num(0.0), ParamUi::Angle),
                p("forceCenter", "Force Center", pt(0.5, 0.5), ParamUi::Point),
                p("directionRandomness", "Direction Randomness", num(10.0), pct()),
                p("speedRandomness", "Speed Randomness", num(10.0), pct()),
                p("gridSpacing", "Grid Spacing", num(10.0), slider(1.0, 500.0, 2.0, 100.0, 0)),
                p("object", "Object", Value::Enum(0), popup(&["Polygon", "Textured Polygon", "Square", "Textured Square"])),
                p("enableDepthSort", "Enable Depth Sort", Value::Bool(true), ParamUi::Checkbox),
                p("startTime", "Start Time (sec)", num(0.0), slider(-1000.0, 1000.0, 0.0, 10.0, 2)),
            ],
            pixel_polly,
        ),
        spec(
            "ec.sim.ccscatterize",
            "CC Scatterize",
            vec![
                p("scatter", "Scatter", num(0.0), slider(0.0, 1000.0, 0.0, 200.0, 1)),
                p("rightTwist", "Right Twist", num(0.0), ParamUi::Angle),
                p("leftTwist", "Left Twist", num(0.0), ParamUi::Angle),
                p("transferMode", "Transfer Mode", Value::Enum(0), popup(&["Composite", "Add"])),
            ],
            scatterize,
        ),
        spec("ec.sim.carddance", "Card Dance", card_dance_params(), card_dance),
        spec(
            "ec.sim.caustics",
            "Caustics",
            vec![
                p("bottom/bottom", "Bottom", Value::Layer(None), ParamUi::Layer),
                p("bottom/scaling", "Scaling", num(1.0), slider(0.01, 10.0, 0.1, 3.0, 3)),
                p("bottom/repeatMode", "Repeat Mode", Value::Enum(2), popup(&["Once", "Tiled", "Reflected"])),
                p("bottom/bottomSizeDiffers", "If Layer Size Differs", Value::Enum(1), popup(&["Center", "Stretch to Fit"])),
                p("bottom/blur", "Blur", num(0.0), slider(0.0, 100.0, 0.0, 20.0, 1)),
                p("water/waterSurface", "Water Surface", Value::Layer(None), ParamUi::Layer),
                p("water/waveHeight", "Wave Height", num(0.2), slider(-1.0, 1.0, -1.0, 1.0, 3)),
                p("water/smoothing", "Smoothing", num(5.0), slider(0.0, 100.0, 0.0, 50.0, 1)),
                p("water/waterDepth", "Water Depth", num(0.1), slider(0.0, 1.0, 0.0, 1.0, 3)),
                p("water/refractiveIndex", "Refractive Index", num(1.2), slider(1.0, 3.0, 1.0, 2.0, 3)),
                p("water/surfaceColor", "Surface Color", col(1.0, 1.0, 1.0), ParamUi::Color),
                p("water/surfaceOpacity", "Surface Opacity", num(0.3), slider(0.0, 1.0, 0.0, 1.0, 3)),
                p("water/causticsStrength", "Caustics Strength", num(0.0), slider(0.0, 1.0, 0.0, 1.0, 3)),
                p("lighting/lightIntensity", "Light Intensity", num(1.0), slider(0.0, 4.0, 0.0, 2.0, 2)),
                p("lighting/lightColor", "Light Color", col(1.0, 1.0, 1.0), ParamUi::Color),
                p("lighting/lightPosition", "Light Position", pt(0.0, 0.0), ParamUi::Point),
                p("lighting/lightHeight", "Light Height", num(1.0), slider(0.0, 10.0, 0.0, 4.0, 2)),
                p("lighting/ambientLight", "Ambient Light", num(0.35), slider(0.0, 2.0, 0.0, 1.0, 2)),
                p("material/diffuse", "Diffuse Reflection", num(0.75), slider(0.0, 2.0, 0.0, 1.0, 2)),
                p("material/specular", "Specular Reflection", num(0.2), slider(0.0, 2.0, 0.0, 1.0, 2)),
                p("material/highlightSharpness", "Highlight Sharpness", num(15.0), slider(1.0, 100.0, 1.0, 100.0, 1)),
            ],
            caustics,
        ),
        spec(
            "ec.sim.waveworld",
            "Wave World",
            {
                let mut v = vec![
                    p("view", "View", Value::Enum(0), popup(&["Wireframe Preview", "Height Map"])),
                    p("heightMapControls/brightness", "Brightness", num(0.5), slider(-1.0, 2.0, 0.0, 1.0, 3)),
                    p("heightMapControls/contrast", "Contrast", num(0.75), slider(0.0, 4.0, 0.0, 2.0, 3)),
                    p("heightMapControls/gamma", "Gamma Adjustment", num(1.0), slider(0.01, 10.0, 0.2, 5.0, 3)),
                    p("heightMapControls/transparency", "Transparency", num(0.0), slider(0.0, 1.0, 0.0, 1.0, 3)),
                    p("simulation/gridResolution", "Grid Resolution", num(60.0), slider(1.0, 400.0, 1.0, 200.0, 0)),
                    p("simulation/gridResDownsamples", "Grid Res Downsamples", Value::Bool(false), ParamUi::Checkbox),
                    p("simulation/waveSpeed", "Wave Speed", num(0.2), slider(0.0, 5.0, 0.0, 1.0, 3)),
                    p("simulation/damping", "Damping", num(0.05), slider(0.0, 5.0, 0.0, 1.0, 3)),
                    p("simulation/reflectEdges", "Reflect Edges", Value::Enum(0), popup(&["None", "Left", "Top", "Right", "Bottom", "All"])),
                    p("simulation/preRoll", "Pre-roll (seconds)", num(0.0), slider(0.0, 30.0, 0.0, 10.0, 2)),
                ];
                v.extend(producer_params(1, 0.5, (0.5, 0.5)));
                v.extend(producer_params(2, 0.0, (0.25, 0.25)));
                v
            },
            wave_world,
        ),
        spec(
            "ec.sim.shatter",
            "Shatter",
            vec![
                p(
                    "view",
                    "View",
                    Value::Enum(1),
                    popup(&["Rendered", "Wireframe Front View", "Wireframe", "Wireframe Front View + Forces", "Wireframe + Forces"]),
                ),
                p("render", "Render", Value::Enum(0), popup(&["All", "Layer", "Pieces"])),
                p("shape/pattern", "Pattern", Value::Enum(0), popup(SHATTER_PATTERNS)),
                p("shape/repetitions", "Repetitions", num(10.0), slider(1.0, 500.0, 1.0, 100.0, 2)),
                p("shape/direction", "Direction", num(0.0), ParamUi::Angle),
                p("shape/origin", "Origin", pt(0.5, 0.5), ParamUi::Point),
                p("shape/extrusionDepth", "Extrusion Depth", num(0.05), slider(0.0, 1.0, 0.0, 1.0, 3)),
                p("force1/force1Position", "Position", pt(0.5, 0.5), ParamUi::Point),
                p("force1/force1Depth", "Depth", num(0.1), slider(-1.0, 1.0, -1.0, 1.0, 3)),
                p("force1/force1Radius", "Radius", num(0.4), slider(0.0, 4.0, 0.0, 2.0, 3)),
                p("force1/force1Strength", "Strength", num(5.0), slider(-20.0, 20.0, -10.0, 10.0, 2)),
                p("force2/force2Position", "Position", pt(0.25, 0.25), ParamUi::Point),
                p("force2/force2Depth", "Depth", num(0.1), slider(-1.0, 1.0, -1.0, 1.0, 3)),
                p("force2/force2Radius", "Radius", num(0.0), slider(0.0, 4.0, 0.0, 2.0, 3)),
                p("force2/force2Strength", "Strength", num(5.0), slider(-20.0, 20.0, -10.0, 10.0, 2)),
                p("physics/rotationSpeed", "Rotation Speed", num(0.2), slider(0.0, 5.0, 0.0, 1.0, 3)),
                p("physics/tumbleAxis", "Tumble Axis", Value::Enum(0), popup(&["Free", "None", "X", "Y", "Z", "XY", "XZ", "YZ"])),
                p("physics/randomness", "Randomness", num(0.1), slider(0.0, 1.0, 0.0, 1.0, 3)),
                p("physics/viscosity", "Viscosity", num(0.1), slider(0.0, 1.0, 0.0, 1.0, 3)),
                p("physics/massVariance", "Mass Variance", num(30.0), pct()),
                p("physics/gravity", "Gravity", num(3.0), slider(0.0, 100.0, 0.0, 10.0, 2)),
                p("physics/gravityDirection", "Gravity Direction", num(180.0), ParamUi::Angle),
                p("physics/gravityInclination", "Gravity Inclination", num(0.0), slider(-90.0, 90.0, -90.0, 90.0, 1)),
                p("lighting/lightIntensity", "Light Intensity", num(1.0), slider(0.0, 4.0, 0.0, 2.0, 2)),
                p("lighting/ambientLight", "Ambient Light", num(0.25), slider(0.0, 2.0, 0.0, 1.0, 2)),
                p("randomSeed", "Random Seed", num(0.0), slider(0.0, 10_000.0, 0.0, 1000.0, 0)),
            ],
            shatter,
        ),
        spec(
            "ec.sim.foam",
            "Foam",
            vec![
                p("view", "View", Value::Enum(0), popup(&["Draft", "Draft + Flow Map", "Rendered"])),
                p("producer/producerPoint", "Producer Point", pt(0.5, 0.5), ParamUi::Point),
                p("producer/producerXSize", "Producer X Size", num(0.05), slider(0.0, 2.0, 0.0, 1.0, 3)),
                p("producer/producerYSize", "Producer Y Size", num(0.05), slider(0.0, 2.0, 0.0, 1.0, 3)),
                p("producer/producerOrientation", "Producer Orientation", num(0.0), ParamUi::Angle),
                p("producer/productionRate", "Production Rate", num(1.0), slider(0.0, 50.0, 0.0, 10.0, 3)),
                p("bubbles/size", "Size", num(0.5), slider(0.0, 10.0, 0.0, 2.0, 3)),
                p("bubbles/sizeVariance", "Size Variance", num(0.5), slider(0.0, 1.0, 0.0, 1.0, 3)),
                p("bubbles/lifespan", "Lifespan", num(300.0), slider(1.0, 30_000.0, 1.0, 1000.0, 1)),
                p("bubbles/growthSpeed", "Bubble Growth Speed", num(0.1), slider(0.0001, 10.0, 0.0001, 1.0, 3)),
                p("bubbles/strength", "Strength", num(10.0), slider(0.0, 100.0, 0.0, 20.0, 2)),
                p("physics/initialSpeed", "Initial Speed", num(0.0), slider(-100.0, 100.0, -10.0, 10.0, 3)),
                p("physics/initialDirection", "Initial Direction", num(0.0), ParamUi::Angle),
                p("physics/windSpeed", "Wind Speed", num(0.5), slider(-100.0, 100.0, -10.0, 10.0, 3)),
                p("physics/windDirection", "Wind Direction", num(90.0), ParamUi::Angle),
                p("physics/turbulence", "Turbulence", num(0.5), slider(0.0, 10.0, 0.0, 2.0, 3)),
                p("physics/repulsion", "Repulsion", num(1.0), slider(0.0, 10.0, 0.0, 2.0, 3)),
                p("physics/viscosity", "Viscosity", num(0.1), slider(0.0, 1.0, 0.0, 1.0, 3)),
                p("physics/stickiness", "Stickiness", num(0.75), slider(0.0, 1.0, 0.0, 1.0, 3)),
                p("zoom", "Zoom", num(1.0), slider(0.01, 50.0, 0.1, 5.0, 3)),
                p("universeSize", "Universe Size", num(1.0), slider(0.01, 10.0, 0.5, 3.0, 3)),
                p("rendering/blendMode", "Blend Mode", Value::Enum(0), popup(&["Transparent", "Solid Old on Top", "Solid New on Top"])),
                p("rendering/bubbleTexture", "Bubble Texture", Value::Enum(0), popup(&["Default Bubble", "Spit", "Bubblegum", "Dishwater", "Milky"])),
                p("randomSeed", "Random Seed", num(1.0), slider(0.0, 10_000.0, 0.0, 1000.0, 0)),
            ],
            foam,
        ),
    ]
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{EffectEnv, run_fx};

    fn ramp(w: u32, hh: u32) -> Image {
        let mut img = Image::new(w, hh);
        for y in 0..hh {
            for x in 0..w {
                img.set(x, y, [x as f32 / w as f32, y as f32 / hh as f32, 0.4, 1.0]);
            }
        }
        img
    }

    fn run(id: &str, vals: &[(&str, Value)], img: Image, t: f64) -> Image {
        run_fx(id, vals, img, t, EffectEnv::default()).img
    }

    fn max_diff(a: &Image, b: &Image) -> f32 {
        a.data.iter().zip(&b.data).map(|(p, q)| (0..4).map(|k| (p[k] - q[k]).abs()).fold(0.0, f32::max)).fold(0.0, f32::max)
    }

    fn sum_diff(a: &Image, b: &Image) -> f32 {
        a.data.iter().zip(&b.data).map(|(p, q)| (0..4).map(|k| (p[k] - q[k]).abs()).sum::<f32>()).sum()
    }

    #[test]
    fn piece_at_rest_is_identity() {
        let src = ramp(16, 16);
        let cam = Cam { c: [8.0, 8.0], d: 64.0 };
        let id = rot_axis([1.0, 0.0, 0.0], 0.0);
        let pc = Piece::new(&[[0.0, 0.0], [16.0, 0.0], [16.0, 16.0], [0.0, 16.0]], [8.0, 8.0], &id, [8.0, 8.0, 0.0], cam).unwrap();
        let mut out = Image::new(16, 16);
        draw_pieces(&mut out, &[pc], &src, None);
        assert!(max_diff(&out, &src) < 1e-4);
    }

    #[test]
    fn ball_action_draws_balls() {
        let v = [("ballSize", num(80.0))];
        let a = run("ec.sim.ccballaction", &v, ramp(32, 32), 0.0);
        assert_eq!(a, run("ec.sim.ccballaction", &v, ramp(32, 32), 0.0));
        assert!(a.data.iter().any(|p| p[3] > 0.9) && a.data.iter().any(|p| p[3] == 0.0), "balls with gaps");
        let none = run("ec.sim.ccballaction", &[("ballSize", num(0.0))], ramp(32, 32), 0.0);
        assert!(none.data.iter().all(|p| p[3] == 0.0));
        let sc = run("ec.sim.ccballaction", &[("ballSize", num(80.0)), ("scatter", num(20.0))], ramp(32, 32), 0.0);
        assert!(sum_diff(&a, &sc) > 1.0);
    }

    #[test]
    fn pixel_polly_breaks_after_start() {
        let v = [("forceCenter", pt(16.0, 16.0)), ("gridSpacing", num(4.0))];
        let before = run("ec.sim.ccpixelpolly", &v, ramp(32, 32), 0.0);
        assert_eq!(before, ramp(32, 32), "intact before the start time");
        let a = run("ec.sim.ccpixelpolly", &v, ramp(32, 32), 0.5);
        assert_eq!(a, run("ec.sim.ccpixelpolly", &v, ramp(32, 32), 0.5));
        assert!(sum_diff(&a, &ramp(32, 32)) > 10.0);
        let tex = run("ec.sim.ccpixelpolly", &[("forceCenter", pt(16.0, 16.0)), ("gridSpacing", num(4.0)), ("object", Value::Enum(3))], ramp(32, 32), 0.5);
        assert!(sum_diff(&a, &tex) > 0.1);
    }

    #[test]
    fn scatterize_identity_and_scatter() {
        assert_eq!(run("ec.sim.ccscatterize", &[], ramp(24, 24), 0.0), ramp(24, 24));
        let a = run("ec.sim.ccscatterize", &[("scatter", num(5.0))], ramp(24, 24), 0.0);
        assert_eq!(a, run("ec.sim.ccscatterize", &[("scatter", num(5.0))], ramp(24, 24), 0.0));
        assert!(sum_diff(&a, &ramp(24, 24)) > 1.0);
        let tw = run("ec.sim.ccscatterize", &[("leftTwist", num(80.0)), ("rightTwist", num(80.0))], ramp(24, 24), 0.0);
        assert!(sum_diff(&tw, &ramp(24, 24)) > 1.0);
    }

    #[test]
    fn card_dance_identity_and_rotation() {
        let src = ramp(30, 20);
        let a = run("ec.sim.carddance", &[], src.clone(), 0.0);
        assert!(max_diff(&a, &src) < 0.02, "flat cards reproduce the layer: {}", max_diff(&a, &src));
        let r = run("ec.sim.carddance", &[("yRotation/yRotSource", Value::Enum(1)), ("yRotation/yRotMultiplier", num(90.0))], src.clone(), 0.0);
        assert_eq!(r, run("ec.sim.carddance", &[("yRotation/yRotSource", Value::Enum(1)), ("yRotation/yRotMultiplier", num(90.0))], src.clone(), 0.0));
        assert!(sum_diff(&r, &src) > 5.0);
        let z = run("ec.sim.carddance", &[("zPosition/zPosOffset", num(-1.0))], src.clone(), 0.0);
        assert!(sum_diff(&z, &src) > 5.0, "cards pulled towards the camera grow");
    }

    #[test]
    fn shatter_at_rest_then_breaks() {
        let v = [("view", Value::Enum(0)), ("force1/force1Position", pt(16.0, 16.0)), ("shape/origin", pt(16.0, 16.0))];
        let src = ramp(32, 32);
        let t0 = run("ec.sim.shatter", &v, src.clone(), 0.0);
        assert!(max_diff(&t0, &src) < 0.03, "{}", max_diff(&t0, &src));
        let t1 = run("ec.sim.shatter", &v, src.clone(), 0.5);
        assert_eq!(t1, run("ec.sim.shatter", &v, src.clone(), 0.5));
        assert!(sum_diff(&t1, &src) > 10.0);
        for pat in 0..SHATTER_PATTERNS.len() as u32 {
            let vv =
                [("view", Value::Enum(0)), ("shape/pattern", Value::Enum(pat)), ("force1/force1Position", pt(16.0, 16.0)), ("shape/origin", pt(16.0, 16.0))];
            let r = run("ec.sim.shatter", &vv, src.clone(), 0.0);
            assert!(max_diff(&r, &src) < 0.05, "pattern {pat} tiles the layer: {}", max_diff(&r, &src));
        }
        let wire = run("ec.sim.shatter", &[("shape/repetitions", num(3.0))], src.clone(), 0.0);
        assert!(wire.data.iter().any(|p| p[3] > 0.5) && wire.data.iter().any(|p| p[3] == 0.0));
        let layer_only =
            run("ec.sim.shatter", &[("view", Value::Enum(0)), ("render", Value::Enum(1)), ("force1/force1Position", pt(16.0, 16.0))], src.clone(), 0.5);
        assert!(layer_only.get(16, 16)[3] == 0.0, "broken centre removed");
    }

    #[test]
    fn caustics_flat_water() {
        let src = ramp(24, 24);
        let a = run(
            "ec.sim.caustics",
            &[
                ("water/surfaceOpacity", num(0.0)),
                ("lighting/ambientLight", num(0.0)),
                ("material/diffuse", num(1.0)),
                ("lighting/lightHeight", num(1000.0)),
                ("material/specular", num(0.0)),
            ],
            src.clone(),
            0.0,
        );
        assert!(max_diff(&a, &src) < 0.01, "flat water, light overhead = bottom: {}", max_diff(&a, &src));
        let b = run("ec.sim.caustics", &[], src.clone(), 0.0);
        assert_eq!(b, run("ec.sim.caustics", &[], src.clone(), 0.0));
        assert!(sum_diff(&b, &src) > 0.1);
    }

    #[test]
    fn wave_world_seek_and_waves() {
        let v = vec![("view", Value::Enum(1)), ("producer1/producer1Position", pt(16.0, 16.0)), ("simulation/gridResolution", num(24.0))];
        let _ = run("ec.sim.waveworld", &v, Image::new(32, 32), 0.5);
        let a = run("ec.sim.waveworld", &v, Image::new(32, 32), 1.0);
        let mut v2 = v.clone();
        v2.push(("heightMapControls/transparency", num(0.0)));
        assert_eq!(a, run("ec.sim.waveworld", &v2, Image::new(32, 32), 1.0));
        // Waves spread: some pixels differ from the flat-water grey.
        assert!(a.data.iter().any(|p| (p[0] - 0.5).abs() > 0.05), "waves");
        let flat = run("ec.sim.waveworld", &[("view", Value::Enum(1)), ("producer1/producer1Amplitude", num(0.0))], Image::new(32, 32), 1.0);
        assert!(flat.data.iter().all(|p| (p[0] - 0.5).abs() < 1e-5));
        let wire =
            run("ec.sim.waveworld", &[("producer1/producer1Position", pt(16.0, 16.0)), ("simulation/gridResolution", num(10.0))], Image::new(32, 32), 0.3);
        assert!(wire.data.iter().any(|p| p[1] > 0.3));
    }

    #[test]
    fn wave_world_steps_match_direct() {
        // Fresh caches: resumed simulation equals simulation from scratch.
        let v = vec![
            ("view", Value::Enum(1)),
            ("producer1/producer1Position", pt(16.0, 16.0)),
            ("simulation/gridResolution", num(20.0)),
            ("simulation/damping", num(0.07)),
        ];
        let a = run("ec.sim.waveworld", &v, Image::new(32, 32), 1.3);
        let mut v2 = v.clone();
        v2.push(("simulation/damping", num(0.07000001)));
        // Different key: computed from scratch at 1.3 directly vs via 0.4 (both fresh keys).
        let _ = run("ec.sim.waveworld", &v2, Image::new(32, 32), 0.4);
        let b = run("ec.sim.waveworld", &v2, Image::new(32, 32), 1.3);
        assert!(max_diff(&a, &b) < 1e-3, "{}", max_diff(&a, &b));
    }

    #[test]
    fn foam_bubbles_drift_and_seek() {
        let v = vec![("producer/producerPoint", pt(16.0, 16.0)), ("view", Value::Enum(2)), ("producer/productionRate", num(2.0))];
        let none = run("ec.sim.foam", &v, Image::new(32, 32), 0.0);
        assert!(none.data.iter().all(|p| p[3] == 0.0));
        let _ = run("ec.sim.foam", &v, Image::new(32, 32), 0.6);
        let a = run("ec.sim.foam", &v, Image::new(32, 32), 1.2);
        let mut v2 = v.clone();
        v2.push(("randomSeed", num(1.0)));
        assert_eq!(a, run("ec.sim.foam", &v2, Image::new(32, 32), 1.2));
        assert!(a.data.iter().any(|p| p[3] > 0.05), "bubbles");
        let draft = run("ec.sim.foam", &[("producer/producerPoint", pt(16.0, 16.0)), ("producer/productionRate", num(2.0))], Image::new(32, 32), 1.0);
        assert!(draft.data.iter().any(|p| p[3] > 0.05));
    }

    #[test]
    fn foam_strength_controls_early_popping() {
        // Strong bubbles all live their full lifespan; weak ones pop at random earlier.
        assert_eq!(foam_pop_age(7, 300.0, 0.0, 1), 300.0);
        let early = (0..200).filter(|&id| foam_pop_age(id, 300.0, 1.0, 1) < 150.0).count();
        assert!(early > 60 && early < 140, "{early}");
        let count = |strength: f64| {
            let v = vec![
                ("producer/producerPoint", pt(16.0, 16.0)),
                ("producer/productionRate", num(3.0)),
                ("bubbles/lifespan", num(40.0)),
                ("bubbles/strength", num(strength)),
                ("physics/windSpeed", num(0.0)),
            ];
            run("ec.sim.foam", &v, Image::new(32, 32), 1.5).data.iter().map(|p| p[3]).sum::<f32>()
        };
        assert!(count(0.0) < count(20.0) * 0.9, "{} vs {}", count(0.0), count(20.0));
    }
}