Function cross

docs/app/js/sanddance-app.js:69981–69986

(out, a, b)

    return a[0] * b[0] + a[1] * b[1];
}
function cross(out, a, b) {
    var z = a[0] * b[1] - a[1] * b[0];
    out[0] = out[1] = 0;
    out[2] = z;
    return out;
}
function lerp(out, a, b, t) {
    var ax = a[0], ay = a[1];
    out[0] = ax + t * (b[0] - ax);