// 把使用 element 表示的數據轉換成無需 element 的數據
export function unindex(positions:number[][], cells:number[][], out?) {
    const dims = positions.length ? positions[0].length : 0;
    const points = cells.length ? cells[0].length : 0;

    out = out || new Float32Array(cells.length * points * dims);

    if (points === 3 && dims === 2) {
        for (let i = 0, n = 0, l = cells.length; i < l; i += 1) {
            const cell = cells[i];
            out[n++] = positions[cell[0]][0];
            out[n++] = positions[cell[0]][1];
            out[n++] = positions[cell[1]][0];
            out[n++] = positions[cell[1]][1];
            out[n++] = positions[cell[2]][0];
            out[n++] = positions[cell[2]][1];
        }
    } else if (points === 3 && dims === 3) {
        for (let i = 0, n = 0, l = cells.length; i < l; i += 1) {
            const cell = cells[i];
            out[n++] = positions[cell[0]][0];
            out[n++] = positions[cell[0]][1];
            out[n++] = positions[cell[0]][2];
            out[n++] = positions[cell[1]][0];
            out[n++] = positions[cell[1]][1];
            out[n++] = positions[cell[1]][2];
            out[n++] = positions[cell[2]][0];
            out[n++] = positions[cell[2]][1];
            out[n++] = positions[cell[2]][2];
        }
    } else {
        console.log('dims:', dims, 'points:', points);
    }
    return out;
}