// 13-step grayscale bars (Y 64..940 in even 73-code steps), Rec.709, 10-bit
// Y'CbCr, packed as v210 (4:2:2). Chroma neutral.
// One work-item per 16-byte block = 6 pixels (6 Y + 3 Cb + 3 Cr).

struct Params {
    width: u32,
    height: u32,
    frame: u32, // animation tick (0,1,2,... per generated frame), NOT the raw grain index
    _pad0: u32,
};

@group(0) @binding(0) var<storage, read_write> out: array<u32>;
@group(0) @binding(1) var<uniform> params: Params;

fn bar_index(px: u32) -> u32 {
    return min((px * 13u) / params.width, 12u);
}

@compute @workgroup_size(64)
fn main(@builtin(global_invocation_id) gid: vec3<u32>) {
    let block = gid.x;
    let total = (params.width * params.height) / 6u;
    if (block >= total) {
        return;
    }

    let y_tab  = array<u32, 13>(64u, 137u, 210u, 283u, 356u, 429u, 502u, 575u, 648u, 721u, 794u, 867u, 940u);

    // 6 = pixels per v210 block (NOT the bar count)
    let x = (block * 6u) % params.width;
    var y: array<u32, 6>;
    var cb: array<u32, 6>;
    var cr: array<u32, 6>;
    for (var i = 0u; i < 6u; i++) {
        let b = bar_index(x + i);
        y[i] = y_tab[b];
        cb[i] = 512u;
        cr[i] = 512u;
    }

    // v210 word layout, chroma co-sited with luma samples 0/2/4:
    // w0 = Cb0|Y0<<10|Cr0<<20; w1 = Y1|Cb2<<10|Y2<<20;
    // w2 = Cr2|Y3<<10|Cb4<<20; w3 = Y4|Cr4<<10|Y5<<20
    out[block * 4u + 0u] = (cb[0] & 0x3FFu) | ((y[0] & 0x3FFu) << 10u) | ((cr[0] & 0x3FFu) << 20u);
    out[block * 4u + 1u] = (y[1] & 0x3FFu) | ((cb[2] & 0x3FFu) << 10u) | ((y[2] & 0x3FFu) << 20u);
    out[block * 4u + 2u] = (cr[2] & 0x3FFu) | ((y[3] & 0x3FFu) << 10u) | ((cb[4] & 0x3FFu) << 20u);
    out[block * 4u + 3u] = (y[4] & 0x3FFu) | ((cr[4] & 0x3FFu) << 10u) | ((y[5] & 0x3FFu) << 20u);
}