Function angle

docs/app/js/sanddance-app.js:70032–70037

(a, b)

    return out;
}
function angle(a, b) {
    var x1 = a[0], y1 = a[1], x2 = b[0], y2 = b[1], // mag is the product of the magnitudes of a and b
    mag = Math.sqrt(x1 * x1 + y1 * y1) * Math.sqrt(x2 * x2 + y2 * y2), // mag &&.. short circuits if mag == 0
    cosine = mag && (x1 * x2 + y1 * y2) / mag; // Math.min(Math.max(cosine, -1), 1) clamps the cosine between -1 and 1
    return Math.acos(Math.min(Math.max(cosine, -1), 1));
}
function zero(out) {
    out[0] = 0.0;
    out[1] = 0.0;