| 1 | function Natural(context) {
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| 2 | this._context = context;
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| 3 | }
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| 4 |
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| 5 | Natural.prototype = {
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| 6 | areaStart: function() {
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| 7 | this._line = 0;
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| 8 | },
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| 9 | areaEnd: function() {
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| 10 | this._line = NaN;
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| 11 | },
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| 12 | lineStart: function() {
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| 13 | this._x = [];
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| 14 | this._y = [];
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| 15 | },
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| 16 | lineEnd: function() {
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| 17 | var x = this._x,
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| 18 | y = this._y,
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| 19 | n = x.length;
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| 20 |
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| 21 | if (n) {
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| 22 | this._line ? this._context.lineTo(x[0], y[0]) : this._context.moveTo(x[0], y[0]);
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| 23 | if (n === 2) {
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| 24 | this._context.lineTo(x[1], y[1]);
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| 25 | } else {
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| 26 | var px = controlPoints(x),
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| 27 | py = controlPoints(y);
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| 28 | for (var i0 = 0, i1 = 1; i1 < n; ++i0, ++i1) {
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| 29 | this._context.bezierCurveTo(px[0][i0], py[0][i0], px[1][i0], py[1][i0], x[i1], y[i1]);
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| 30 | }
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| 31 | }
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| 32 | }
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| 33 |
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| 34 | if (this._line || (this._line !== 0 && n === 1)) this._context.closePath();
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| 35 | this._line = 1 - this._line;
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| 36 | this._x = this._y = null;
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| 37 | },
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| 38 | point: function(x, y) {
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| 39 | this._x.push(+x);
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| 40 | this._y.push(+y);
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| 41 | }
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| 42 | };
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| 43 |
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| 44 | // See https://www.particleincell.com/2012/bezier-splines/ for derivation.
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| 45 | function controlPoints(x) {
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| 46 | var i,
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| 47 | n = x.length - 1,
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| 48 | m,
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| 49 | a = new Array(n),
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| 50 | b = new Array(n),
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| 51 | r = new Array(n);
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| 52 | a[0] = 0, b[0] = 2, r[0] = x[0] + 2 * x[1];
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| 53 | 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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| 54 | a[n - 1] = 2, b[n - 1] = 7, r[n - 1] = 8 * x[n - 1] + x[n];
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| 55 | 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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| 56 | a[n - 1] = r[n - 1] / b[n - 1];
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| 57 | for (i = n - 2; i >= 0; --i) a[i] = (r[i] - a[i + 1]) / b[i];
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| 58 | b[n - 1] = (x[n] + a[n - 1]) / 2;
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| 59 | for (i = 0; i < n - 1; ++i) b[i] = 2 * x[i + 1] - a[i + 1];
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| 60 | return [a, b];
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| 61 | }
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| 62 |
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| 63 | export default function(context) {
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| 64 | return new Natural(context);
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| 65 | }
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