Function Cardinal

docs/app/js/sanddance-app.js:125959–125962

(context, tension)

    that._context.bezierCurveTo(that._x1 + that._k * (that._x2 - that._x0), that._y1 + that._k * (that._y2 - that._y0), that._x2 + that._k * (that._x1 - x), that._y2 + that._k * (that._y1 - y), that._x2, that._y2);
}
function Cardinal(context, tension) {
    this._context = context;
    this._k = (1 - tension) / 6;
}
Cardinal.prototype = {
    areaStart: function() {
        this._line = 0;