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