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Filename : index.js
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/**
 * Flot plugin that provides spline interpolation for line graphs
 * author: Alex Bardas < alex.bardas@gmail.com >
 * modified by: Avi Kohn https://github.com/AMKohn
 * based on the spline interpolation described at:
 *		 http://scaledinnovation.com/analytics/splines/aboutSplines.html
 *
 * Example usage: (add in plot options series object)
 *		for linespline:
 *			series: {
 *				...
 *				lines: {
 *					show: false
 *				},
 *				splines: {
 *					show: true,
 *					tension: x, (float between 0 and 1, defaults to 0.5),
 *					lineWidth: y (number, defaults to 2),
 *					fill: z (float between 0 .. 1 or false, as in flot documentation)
 *				},
 *				...
 *			}
 *		areaspline:
 *			series: {
 *				...
 *				lines: {
 *					show: true,
 *					lineWidth: 0, (line drawing will not execute)
 *					fill: x, (float between 0 .. 1, as in flot documentation)
 *					...
 *				},
 *				splines: {
 *					show: true,
 *					tension: 0.5 (float between 0 and 1)
 *				},
 *				...
 *			}
 *
 */

(function($) {
	'use strict'

	/**
	 * @param {Number} x0, y0, x1, y1: coordinates of the end (knot) points of the segment
	 * @param {Number} x2, y2: the next knot (not connected, but needed to calculate p2)
	 * @param {Number} tension: control how far the control points spread
	 * @return {Array}: p1 -> control point, from x1 back toward x0
	 * 					p2 -> the next control point, returned to become the next segment's p1
	 *
	 * @api private
	 */
	function getControlPoints(x0, y0, x1, y1, x2, y2, tension) {

		var pow = Math.pow,
			sqrt = Math.sqrt,
			d01, d12, fa, fb, p1x, p1y, p2x, p2y;

		//  Scaling factors: distances from this knot to the previous and following knots.
		d01 = sqrt(pow(x1 - x0, 2) + pow(y1 - y0, 2));
		d12 = sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));

		fa = tension * d01 / (d01 + d12);
		fb = tension - fa;

		p1x = x1 + fa * (x0 - x2);
		p1y = y1 + fa * (y0 - y2);

		p2x = x1 - fb * (x0 - x2);
		p2y = y1 - fb * (y0 - y2);

		return [p1x, p1y, p2x, p2y];
	}

	var line = [];

	function drawLine(points, ctx, height, fill, seriesColor) {
		var c = $.color.parse(seriesColor);

		c.a = typeof fill == "number" ? fill : .3;
		c.normalize();
		c = c.toString();

		ctx.beginPath();
		ctx.moveTo(points[0][0], points[0][1]);

		var plength = points.length;

		for (var i = 0; i < plength; i++) {
			ctx[points[i][3]].apply(ctx, points[i][2]);
		}

		ctx.stroke();

		ctx.lineWidth = 0;
		ctx.lineTo(points[plength - 1][0], height);
		ctx.lineTo(points[0][0], height);

		ctx.closePath();
		
		if (fill !== false) {
			ctx.fillStyle = c;
			ctx.fill();
		}
	}

	/**
	 * @param {Object} ctx: canvas context
	 * @param {String} type: accepted strings: 'bezier' or 'quadratic' (defaults to quadratic)
	 * @param {Array} points: 2 points for which to draw the interpolation
	 * @param {Array} cpoints: control points for those segment points
	 *
	 * @api private
	 */
	function queue(ctx, type, points, cpoints) {
		if (type === void 0 || (type !== 'bezier' && type !== 'quadratic')) {
			type = 'quadratic';
		}
		type = type + 'CurveTo';

		if (line.length == 0) line.push([points[0], points[1], cpoints.concat(points.slice(2)), type]);
		else if (type == "quadraticCurveTo" && points.length == 2) {
			cpoints = cpoints.slice(0, 2).concat(points);

			line.push([points[0], points[1], cpoints, type]);
		}
		else line.push([points[2], points[3], cpoints.concat(points.slice(2)), type]);
	}

	/**
	 * @param {Object} plot
	 * @param {Object} ctx: canvas context
	 * @param {Object} series
	 *
	 * @api private
	 */

	function drawSpline(plot, ctx, series) {
		// Not interested if spline is not requested
		if (series.splines.show !== true) {
			return;
		}

		var cp = [],
			// array of control points
			tension = series.splines.tension || 0.5,
			idx, x, y, points = series.datapoints.points,
			ps = series.datapoints.pointsize,
			plotOffset = plot.getPlotOffset(),
			len = points.length,
			pts = [];

		line = [];

		// Cannot display a linespline/areaspline if there are less than 3 points
		if (len / ps < 4) {
			$.extend(series.lines, series.splines);
			return;
		}

		for (idx = 0; idx < len; idx += ps) {
			x = points[idx];
			y = points[idx + 1];
			if (x == null || x < series.xaxis.min || x > series.xaxis.max || y < series.yaxis.min || y > series.yaxis.max) {
				continue;
			}

			pts.push(series.xaxis.p2c(x) + plotOffset.left, series.yaxis.p2c(y) + plotOffset.top);
		}

		len = pts.length;

		// Draw an open curve, not connected at the ends
		for (idx = 0; idx < len - 2; idx += 2) {
			cp = cp.concat(getControlPoints.apply(this, pts.slice(idx, idx + 6).concat([tension])));
		}

		ctx.save();
		ctx.strokeStyle = series.color;
		ctx.lineWidth = series.splines.lineWidth;

		queue(ctx, 'quadratic', pts.slice(0, 4), cp.slice(0, 2));

		for (idx = 2; idx < len - 3; idx += 2) {
			queue(ctx, 'bezier', pts.slice(idx, idx + 4), cp.slice(2 * idx - 2, 2 * idx + 2));
		}

		queue(ctx, 'quadratic', pts.slice(len - 2, len), [cp[2 * len - 10], cp[2 * len - 9], pts[len - 4], pts[len - 3]]);

		drawLine(line, ctx, plot.height() + 10, series.splines.fill, series.color);

		ctx.restore();
	}

	$.plot.plugins.push({
		init: function(plot) {
			plot.hooks.drawSeries.push(drawSpline);
		},
		options: {
			series: {
				splines: {
					show: false,
					lineWidth: 2,
					tension: 0.5,
					fill: false
				}
			}
		},
		name: 'spline',
		version: '0.8.2'
	});
})(jQuery);