segrle.js

function segrle({aid, width, height, data}){
    let buf = new Uint8Array(width * height);
    let pos = 0;
    const te = new TextEncoder();
    bytes(te.encode("SegRLEv1"));

    const aidbuf = te.encode(aid);
    code(aidbuf.length);
    bytes(aidbuf);

    const stats = new Map();
    for (const v of data)
        stats.set(v, stats.has(v) ? stats.get(v) + 1 : 1);
    code(stats.size);
    const bytemode = stats.size <= 256;
    let codes = new Map();
    for (const pair of [...stats.entries()].sort((x, y) => y[1] - x[1])) {
        code(atlas.remap[pair[0]]);
        codes.set(pair[0], codes.size);
    }

    code(width);
    code(height);

    let current = -1;
    let count = 0;
    for (const v of data) {
        if (v !== current) {
            if (current !== -1) {
                if (bytemode)
                    byte(codes.get(current));
                else
                    code(codes.get(current));
                code(count);
            }
            current = v;
            count = 0;
        } else
            count++;
    }
    if (bytemode)
        byte(codes.get(current));
    else
        code(codes.get(current));
    code(count);

    resize(pos);
    return buf;

    function resize(newsize) {
        const newbuf = new Uint8Array(newsize);
        const len = Math.min(buf.length, newsize);
        for (let i = 0; i < len; i++)
            newbuf[i] = buf[i];
        buf = newbuf;
    }
    function byte(b) {
        if (buf.length <= pos)
            resize(buf.length * 2);
        buf[pos] = b;
        pos++;
    }
    function bytes(bs) {
        for (const b of bs)
            byte(b);
    }
    function code(c) {
        while (c > 127) {
            byte(c | 128);
            c >>>= 7;
        }
        byte(c);
}
}