Function vAngle

libs/echarts/echarts.simple.js:15191–15194

(u, v)

    return (u[0] * v[0] + u[1] * v[1]) / (vMag(u) * vMag(v));
};
var vAngle = function (u, v) {
    return (u[0] * v[1] < u[1] * v[0] ? -1 : 1)
            * Math.acos(vRatio(u, v));
};

function processArc(x1, y1, x2, y2, fa, fs, rx, ry, psiDeg, cmd, path) {
    var psi = psiDeg * (PI / 180.0);