Function findXYatLength

src/plots/polar/helpers.js:96–108

(l, m, xp, yp)

// where f(x) = m*x + t + yp
// and   (x0, x1) = (-b +/- del) / (2*a)
function findXYatLength(l, m, xp, yp) {
    var t = -m * xp;
    var a = m * m + 1;
    var b = 2 * (m * t - xp);
    var c = t * t + xp * xp - l * l;
    var del = Math.sqrt(b * b - 4 * a * c);
    var x0 = (-b + del) / (2 * a);
    var x1 = (-b - del) / (2 * a);
    return [
        [x0, m * x0 + t + yp],
        [x1, m * x1 + t + yp]
    ];
}

function makeRegularPolygon(r, vangles) {
    var len = vangles.length;