// Demoscene plasma: four sine waves summed and looked up in a palette,
// drawn into 18 frames while two of the waves drift and the palette
// cycles. The last frame leads back into the first, so it loops. Each
// cell is 2x2 pixels: chunkier, and a quarter of the work per frame.
let pal = ["#0A0A1E", "#14193F", "#1B2A6E", "#2E2A57", "#5A1236", "#A51D45",
           "#E02948", "#FF5B3E", "#FFD23C", "#FFF3B0"];
let cell = 2;
let cols = ps.doc_width() / cell;
let rows = ps.doc_height() / cell;
let cx = cols.to_float() / 2.0;
let cy = rows.to_float() / 2.0;
let frames = 18;

// The two waves that stay put, and each cell's distance from the
// center, worked out once.
let still = [];
let ring = [];
for y in 0..rows {
    for x in 0..cols {
        let fx = x.to_float();
        let fy = y.to_float();
        let dx = fx - cx;
        let dy = fy - cy;
        still.push(sin(fx / 5.5) + sin(fy / 3.5));
        ring.push(sqrt(dx * dx + dy * dy) / 3.0);
    }
}

// The palette folded into 18 steps: dark, hot, dark.
let fold = [];
for k in 0..18 {
    let p = if k < 10 { k } else { 18 - k };
    fold.push(pal[p.min(9)]);
}

ps_timeline_set_fps(12);
for f in 0..frames {
    if f > 0 { ps_timeline_add_frame(); }
    let t = f.to_float() * 2.0 * PI() / frames.to_float();
    // The diagonal wave depends only on x + y: one sine per diagonal.
    let diag = [];
    for d in 0..cols + rows { diag.push(sin(d.to_float() / 7.5 + t)); }
    for y in 0..rows {
        for x in 0..cols {
            let i = y * cols + x;
            let v = still[i] + diag[x + y] + sin(ring[i] - t);
            // v runs -4..4. Shift one palette step per frame to cycle.
            let k = (((v + 4.0) * 2.25).floor().to_int() + f) % 18;
            ps.pixel_fill(x * cell, y * cell, x * cell + 1, y * cell + 1, fold[k]);
        }
    }
}
print(`${frames} frames of ${cols * rows} cells from four sine waves`);