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function Natural(context) {
this._context = context;
}
Natural.prototype = {
areaStart: function() {
this._line = 0;
},
areaEnd: function() {
this._line = NaN;
},
lineStart: function() {
this._x = [];
this._y = [];
},
lineEnd: function() {
var x = this._x,
y = this._y,
n = x.length;
if (n) {
this._line ? this._context.lineTo(x[0], y[0]) : this._context.moveTo(x[0], y[0]);
if (n === 2) {
this._context.lineTo(x[1], y[1]);
} else {
var px = controlPoints(x),
py = controlPoints(y);
for (var i0 = 0, i1 = 1; i1 < n; ++i0, ++i1) {
this._context.bezierCurveTo(px[0][i0], py[0][i0], px[1][i0], py[1][i0], x[i1], y[i1]);
}
}
}
if (this._line || (this._line !== 0 && n === 1)) this._context.closePath();
this._line = 1 - this._line;
this._x = this._y = null;
},
point: function(x, y) {
this._x.push(+x);
this._y.push(+y);
}
};
// See https://www.particleincell.com/2012/bezier-splines/ for derivation.
function controlPoints(x) {
var i,
n = x.length - 1,
m,
a = new Array(n),
b = new Array(n),
r = new Array(n);
a[0] = 0, b[0] = 2, r[0] = x[0] + 2 * x[1];
for (i = 1; i < n - 1; ++i) a[i] = 1, b[i] = 4, r[i] = 4 * x[i] + 2 * x[i + 1];
a[n - 1] = 2, b[n - 1] = 7, r[n - 1] = 8 * x[n - 1] + x[n];
for (i = 1; i < n; ++i) m = a[i] / b[i - 1], b[i] -= m, r[i] -= m * r[i - 1];
a[n - 1] = r[n - 1] / b[n - 1];
for (i = n - 2; i >= 0; --i) a[i] = (r[i] - a[i + 1]) / b[i];
b[n - 1] = (x[n] + a[n - 1]) / 2;
for (i = 0; i < n - 1; ++i) b[i] = 2 * x[i + 1] - a[i + 1];
return [a, b];
}
export default function(context) {
return new Natural(context);
}