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+// SPDX-License-Identifier: MIT
+(function() {
+"use strict";
+
+var Dygraph;
+if (window.Dygraph) {
+ Dygraph = window.Dygraph;
+} else if (typeof(module) !== 'undefined') {
+ Dygraph = require('../dygraph');
+}
+
+/**
+ * Given three sequential points, p0, p1 and p2, find the left and right
+ * control points for p1.
+ *
+ * The three points are expected to have x and y properties.
+ *
+ * The alpha parameter controls the amount of smoothing.
+ * If α=0, then both control points will be the same as p1 (i.e. no smoothing).
+ *
+ * Returns [l1x, l1y, r1x, r1y]
+ *
+ * It's guaranteed that the line from (l1x, l1y)-(r1x, r1y) passes through p1.
+ * Unless allowFalseExtrema is set, then it's also guaranteed that:
+ * l1y ∈ [p0.y, p1.y]
+ * r1y ∈ [p1.y, p2.y]
+ *
+ * The basic algorithm is:
+ * 1. Put the control points l1 and r1 α of the way down (p0, p1) and (p1, p2).
+ * 2. Shift l1 and r2 so that the line l1–r1 passes through p1
+ * 3. Adjust to prevent false extrema while keeping p1 on the l1–r1 line.
+ *
+ * This is loosely based on the HighCharts algorithm.
+ */
+function getControlPoints(p0, p1, p2, opt_alpha, opt_allowFalseExtrema) {
+ var alpha = (opt_alpha !== undefined) ? opt_alpha : 1/3; // 0=no smoothing, 1=crazy smoothing
+ var allowFalseExtrema = opt_allowFalseExtrema || false;
+
+ if (!p2) {
+ return [p1.x, p1.y, null, null];
+ }
+
+ // Step 1: Position the control points along each line segment.
+ var l1x = (1 - alpha) * p1.x + alpha * p0.x,
+ l1y = (1 - alpha) * p1.y + alpha * p0.y,
+ r1x = (1 - alpha) * p1.x + alpha * p2.x,
+ r1y = (1 - alpha) * p1.y + alpha * p2.y;
+
+ // Step 2: shift the points up so that p1 is on the l1–r1 line.
+ if (l1x != r1x) {
+ // This can be derived w/ some basic algebra.
+ var deltaY = p1.y - r1y - (p1.x - r1x) * (l1y - r1y) / (l1x - r1x);
+ l1y += deltaY;
+ r1y += deltaY;
+ }
+
+ // Step 3: correct to avoid false extrema.
+ if (!allowFalseExtrema) {
+ if (l1y > p0.y && l1y > p1.y) {
+ l1y = Math.max(p0.y, p1.y);
+ r1y = 2 * p1.y - l1y;
+ } else if (l1y < p0.y && l1y < p1.y) {
+ l1y = Math.min(p0.y, p1.y);
+ r1y = 2 * p1.y - l1y;
+ }
+
+ if (r1y > p1.y && r1y > p2.y) {
+ r1y = Math.max(p1.y, p2.y);
+ l1y = 2 * p1.y - r1y;
+ } else if (r1y < p1.y && r1y < p2.y) {
+ r1y = Math.min(p1.y, p2.y);
+ l1y = 2 * p1.y - r1y;
+ }
+ }
+
+ return [l1x, l1y, r1x, r1y];
+}
+
+// i.e. is none of (null, undefined, NaN)
+function isOK(x) {
+ return !!x && !isNaN(x);
+};
+
+// A plotter which uses splines to create a smooth curve.
+// See tests/plotters.html for a demo.
+// Can be controlled via smoothPlotter.smoothing
+function smoothPlotter(e) {
+ var ctx = e.drawingContext,
+ points = e.points;
+
+ ctx.beginPath();
+ ctx.moveTo(points[0].canvasx, points[0].canvasy);
+
+ // right control point for previous point
+ var lastRightX = points[0].canvasx, lastRightY = points[0].canvasy;
+
+ for (var i = 1; i < points.length; i++) {
+ var p0 = points[i - 1],
+ p1 = points[i],
+ p2 = points[i + 1];
+ p0 = p0 && isOK(p0.canvasy) ? p0 : null;
+ p1 = p1 && isOK(p1.canvasy) ? p1 : null;
+ p2 = p2 && isOK(p2.canvasy) ? p2 : null;
+ if (p0 && p1) {
+ var controls = getControlPoints({x: p0.canvasx, y: p0.canvasy},
+ {x: p1.canvasx, y: p1.canvasy},
+ p2 && {x: p2.canvasx, y: p2.canvasy},
+ smoothPlotter.smoothing);
+ // Uncomment to show the control points:
+ // ctx.lineTo(lastRightX, lastRightY);
+ // ctx.lineTo(controls[0], controls[1]);
+ // ctx.lineTo(p1.canvasx, p1.canvasy);
+ lastRightX = (lastRightX !== null) ? lastRightX : p0.canvasx;
+ lastRightY = (lastRightY !== null) ? lastRightY : p0.canvasy;
+ ctx.bezierCurveTo(lastRightX, lastRightY,
+ controls[0], controls[1],
+ p1.canvasx, p1.canvasy);
+ lastRightX = controls[2];
+ lastRightY = controls[3];
+ } else if (p1) {
+ // We're starting again after a missing point.
+ ctx.moveTo(p1.canvasx, p1.canvasy);
+ lastRightX = p1.canvasx;
+ lastRightY = p1.canvasy;
+ } else {
+ lastRightX = lastRightY = null;
+ }
+ }
+
+ ctx.stroke();
+}
+smoothPlotter.smoothing = 1/3;
+smoothPlotter._getControlPoints = getControlPoints; // for testing
+
+// older versions exported a global.
+// This will be removed in the future.
+// The preferred way to access smoothPlotter is via Dygraph.smoothPlotter.
+window.smoothPlotter = smoothPlotter;
+Dygraph.smoothPlotter = smoothPlotter;
+
+})();