jquery.flot.spline.js

/**
 * 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);