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app/assets/javascripts/jquery.flot.errorbars.js

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/* Flot plugin for plotting error bars.

Copyright (c) 2007-2013 IOLA and Ole Laursen.
Licensed under the MIT license.

Error bars are used to show standard deviation and other statistical
properties in a plot.

* Created by Rui Pereira  -  rui (dot) pereira (at) gmail (dot) com

This plugin allows you to plot error-bars over points. Set "errorbars" inside
the points series to the axis name over which there will be error values in
your data array (*even* if you do not intend to plot them later, by setting
"show: null" on xerr/yerr).

The plugin supports these options:

    series: {
        points: {
            errorbars: "x" or "y" or "xy",
            xerr: {
                show: null/false or true,
                asymmetric: null/false or true,
                upperCap: null or "-" or function,
                lowerCap: null or "-" or function,
                color: null or color,
                radius: null or number
            },
            yerr: { same options as xerr }
        }
    }

Each data point array is expected to be of the type:

    "x"  [ x, y, xerr ]
    "y"  [ x, y, yerr ]
    "xy" [ x, y, xerr, yerr ]

Where xerr becomes xerr_lower,xerr_upper for the asymmetric error case, and
equivalently for yerr. Eg., a datapoint for the "xy" case with symmetric
error-bars on X and asymmetric on Y would be:

    [ x, y, xerr, yerr_lower, yerr_upper ]

By default no end caps are drawn. Setting upperCap and/or lowerCap to "-" will
draw a small cap perpendicular to the error bar. They can also be set to a
user-defined drawing function, with (ctx, x, y, radius) as parameters, as eg.

    function drawSemiCircle( ctx, x, y, radius ) {
        ctx.beginPath();
        ctx.arc( x, y, radius, 0, Math.PI, false );
        ctx.moveTo( x - radius, y );
        ctx.lineTo( x + radius, y );
        ctx.stroke();
    }

Color and radius both default to the same ones of the points series if not
set. The independent radius parameter on xerr/yerr is useful for the case when
we may want to add error-bars to a line, without showing the interconnecting
points (with radius: 0), and still showing end caps on the error-bars.
shadowSize and lineWidth are derived as well from the points series.

*/

(function ($) {
    var options = {
        series: {
            points: {
                errorbars: null, //should be 'x', 'y' or 'xy'
                xerr: { err: 'x', show: null, asymmetric: null, upperCap: null, lowerCap: null, color: null, radius: null},
                yerr: { err: 'y', show: null, asymmetric: null, upperCap: null, lowerCap: null, color: null, radius: null}
            }
        }
    };

    function processRawData(plot, series, data, datapoints){
        if (!series.points.errorbars)
            return;

        // x,y values
        var format = [
            { x: true, number: true, required: true },
            { y: true, number: true, required: true }
        ];

        var errors = series.points.errorbars;
        // error bars - first X then Y
        if (errors == 'x' || errors == 'xy') {
            // lower / upper error
            if (series.points.xerr.asymmetric) {
                format.push({ x: true, number: true, required: true });
                format.push({ x: true, number: true, required: true });
            } else
                format.push({ x: true, number: true, required: true });
        }
        if (errors == 'y' || errors == 'xy') {
            // lower / upper error
            if (series.points.yerr.asymmetric) {
                format.push({ y: true, number: true, required: true });
                format.push({ y: true, number: true, required: true });
            } else
                format.push({ y: true, number: true, required: true });
        }
        datapoints.format = format;
    }

    function parseErrors(series, i){

        var points = series.datapoints.points;

        // read errors from points array
        var exl = null,
                exu = null,
                eyl = null,
                eyu = null;
        var xerr = series.points.xerr,
                yerr = series.points.yerr;

        var eb = series.points.errorbars;
        // error bars - first X
        if (eb == 'x' || eb == 'xy') {
            if (xerr.asymmetric) {
                exl = points[i + 2];
                exu = points[i + 3];
                if (eb == 'xy')
                    if (yerr.asymmetric){
                        eyl = points[i + 4];
                        eyu = points[i + 5];
                    } else eyl = points[i + 4];
            } else {
                exl = points[i + 2];
                if (eb == 'xy')
                    if (yerr.asymmetric) {
                        eyl = points[i + 3];
                        eyu = points[i + 4];
                    } else eyl = points[i + 3];
            }
        // only Y
        } else if (eb == 'y')
            if (yerr.asymmetric) {
                eyl = points[i + 2];
                eyu = points[i + 3];
            } else eyl = points[i + 2];

        // symmetric errors?
        if (exu == null) exu = exl;
        if (eyu == null) eyu = eyl;

        var errRanges = [exl, exu, eyl, eyu];
        // nullify if not showing
        if (!xerr.show){
            errRanges[0] = null;
            errRanges[1] = null;
        }
        if (!yerr.show){
            errRanges[2] = null;
            errRanges[3] = null;
        }
        return errRanges;
    }

    function drawSeriesErrors(plot, ctx, s){

        var points = s.datapoints.points,
                ps = s.datapoints.pointsize,
                ax = [s.xaxis, s.yaxis],
                radius = s.points.radius,
                err = [s.points.xerr, s.points.yerr];

        //sanity check, in case some inverted axis hack is applied to flot
        var invertX = false;
        if (ax[0].p2c(ax[0].max) < ax[0].p2c(ax[0].min)) {
            invertX = true;
            var tmp = err[0].lowerCap;
            err[0].lowerCap = err[0].upperCap;
            err[0].upperCap = tmp;
        }

        var invertY = false;
        if (ax[1].p2c(ax[1].min) < ax[1].p2c(ax[1].max)) {
            invertY = true;
            var tmp = err[1].lowerCap;
            err[1].lowerCap = err[1].upperCap;
            err[1].upperCap = tmp;
        }

        for (var i = 0; i < s.datapoints.points.length; i += ps) {

            //parse
            var errRanges = parseErrors(s, i);

            //cycle xerr & yerr
            for (var e = 0; e < err.length; e++){

                var minmax = [ax[e].min, ax[e].max];

                //draw this error?
                if (errRanges[e * err.length]){

                    //data coordinates
                    var x = points[i],
                        y = points[i + 1];

                    //errorbar ranges
                    var upper = [x, y][e] + errRanges[e * err.length + 1],
                        lower = [x, y][e] - errRanges[e * err.length];

                    //points outside of the canvas
                    if (err[e].err == 'x')
                        if (y > ax[1].max || y < ax[1].min || upper < ax[0].min || lower > ax[0].max)
                            continue;
                    if (err[e].err == 'y')
                        if (x > ax[0].max || x < ax[0].min || upper < ax[1].min || lower > ax[1].max)
                            continue;

                    // prevent errorbars getting out of the canvas
                    var drawUpper = true,
                        drawLower = true;

                    if (upper > minmax[1]) {
                        drawUpper = false;
                        upper = minmax[1];
                    }
                    if (lower < minmax[0]) {
                        drawLower = false;
                        lower = minmax[0];
                    }

                    //sanity check, in case some inverted axis hack is applied to flot
                    if ((err[e].err == 'x' && invertX) || (err[e].err == 'y' && invertY)) {
                        //swap coordinates
                        var tmp = lower;
                        lower = upper;
                        upper = tmp;
                        tmp = drawLower;
                        drawLower = drawUpper;
                        drawUpper = tmp;
                        tmp = minmax[0];
                        minmax[0] = minmax[1];
                        minmax[1] = tmp;
                    }

                    // convert to pixels
                    x = ax[0].p2c(x),
                        y = ax[1].p2c(y),
                        upper = ax[e].p2c(upper);
                    lower = ax[e].p2c(lower);
                    minmax[0] = ax[e].p2c(minmax[0]);
                    minmax[1] = ax[e].p2c(minmax[1]);

                    //same style as points by default
                    var lw = err[e].lineWidth ? err[e].lineWidth : s.points.lineWidth,
                        sw = s.points.shadowSize != null ? s.points.shadowSize : s.shadowSize;

                    //shadow as for points
                    if (lw > 0 && sw > 0) {
                        var w = sw / 2;
                        ctx.lineWidth = w;
                        ctx.strokeStyle = "rgba(0,0,0,0.1)";
                        drawError(ctx, err[e], x, y, upper, lower, drawUpper, drawLower, radius, w + w/2, minmax);

                        ctx.strokeStyle = "rgba(0,0,0,0.2)";
                        drawError(ctx, err[e], x, y, upper, lower, drawUpper, drawLower, radius, w/2, minmax);
                    }

                    ctx.strokeStyle = err[e].color? err[e].color: s.color;
                    ctx.lineWidth = lw;
                    //draw it
                    drawError(ctx, err[e], x, y, upper, lower, drawUpper, drawLower, radius, 0, minmax);
                }
            }
        }
    }

    function drawError(ctx,err,x,y,upper,lower,drawUpper,drawLower,radius,offset,minmax){

        //shadow offset
        y += offset;
        upper += offset;
        lower += offset;

        // error bar - avoid plotting over circles
        if (err.err == 'x'){
            if (upper > x + radius) drawPath(ctx, [[upper,y],[Math.max(x + radius,minmax[0]),y]]);
            else drawUpper = false;
            if (lower < x - radius) drawPath(ctx, [[Math.min(x - radius,minmax[1]),y],[lower,y]] );
            else drawLower = false;
        }
        else {
            if (upper < y - radius) drawPath(ctx, [[x,upper],[x,Math.min(y - radius,minmax[0])]] );
            else drawUpper = false;
            if (lower > y + radius) drawPath(ctx, [[x,Math.max(y + radius,minmax[1])],[x,lower]] );
            else drawLower = false;
        }

        //internal radius value in errorbar, allows to plot radius 0 points and still keep proper sized caps
        //this is a way to get errorbars on lines without visible connecting dots
        radius = err.radius != null? err.radius: radius;

        // upper cap
        if (drawUpper) {
            if (err.upperCap == '-'){
                if (err.err=='x') drawPath(ctx, [[upper,y - radius],[upper,y + radius]] );
                else drawPath(ctx, [[x - radius,upper],[x + radius,upper]] );
            } else if ($.isFunction(err.upperCap)){
                if (err.err=='x') err.upperCap(ctx, upper, y, radius);
                else err.upperCap(ctx, x, upper, radius);
            }
        }
        // lower cap
        if (drawLower) {
            if (err.lowerCap == '-'){
                if (err.err=='x') drawPath(ctx, [[lower,y - radius],[lower,y + radius]] );
                else drawPath(ctx, [[x - radius,lower],[x + radius,lower]] );
            } else if ($.isFunction(err.lowerCap)){
                if (err.err=='x') err.lowerCap(ctx, lower, y, radius);
                else err.lowerCap(ctx, x, lower, radius);
            }
        }
    }

    function drawPath(ctx, pts){
        ctx.beginPath();
        ctx.moveTo(pts[0][0], pts[0][1]);
        for (var p=1; p < pts.length; p++)
            ctx.lineTo(pts[p][0], pts[p][1]);
        ctx.stroke();
    }

    function draw(plot, ctx){
        var plotOffset = plot.getPlotOffset();

        ctx.save();
        ctx.translate(plotOffset.left, plotOffset.top);
        $.each(plot.getData(), function (i, s) {
            if (s.points.errorbars && (s.points.xerr.show || s.points.yerr.show))
                drawSeriesErrors(plot, ctx, s);
        });
        ctx.restore();
    }

    function init(plot) {
        plot.hooks.processRawData.push(processRawData);
        plot.hooks.draw.push(draw);
    }

    $.plot.plugins.push({
                init: init,
                options: options,
                name: 'errorbars',
                version: '1.0'
            });
})(jQuery);