How to shade between 2 lines on a line graph using chart.js version2

Question

I'm new to chart.js and I'm having trouble shading between 2 lines on a line graph. Below is an example of what id like to achieve:

This is an example of what im after

but the base functionality in chart.js version 2 seems to only shade between a line and 0 on the y-axis.

Here is the code for the graph I have so far. I would like to shade between the GTUpper and GTLower lines as these describe a range.

<html>
    <div>
        <canvas id="myChart"></canvas>
    </div>
</html>


<script>

function GenGraph(y) {
    // function to generate the graph with chart.js

    $(document).ready(function(){
    var roomCap = 220
    var prediction = [62, 65, 135, 145, 140, 120, 135, 189, 180, 175, 100, 25]
    var gndTruthUpper = [75, 100, 150, 175, 150, 150, 175, 200, 175, 150, 125, 100]
    var gndTruthLower = [50, 50, 75, 50, 25, 50, 75, 100, 125, 150, 125, 100, 75]

    var data = {
        labels: ["00", "05", "10", "15", "20", "25", "30", "35", "40", "45", "50", "55"],
            datasets: [{
                label: 'prediction',
                fill: false,
                pointRadius: 0,
                borderColor: 'blue',
                data: prediction
            },{
                label: 'GTUpper',
                fill: true,
                pointRadius: 0,
                borderDash: [10, 10],
                borderColor: 'black',
                data: gndTruthUpper   
           },{
                label: 'GTLower',
                fill: false,
                pointRadius: 0,
                borderDash: [10, 10],
                borderColor: 'black',
                data: gndTruthLower  
           }]
       };
       var options = {
           scales: {
               yAxes: [{
                   ticks: {
                       min: 0,
                       max: roomCap
                   }
               }]
           }
       };

       var ctx = document.getElementById("myChart").getContext("2d");
       var myChart = new Chart(ctx, {
           type: 'line',
           data: data,
           options: options
       });     
    });    
};

</script>

My issue is that any similar stackoverflow posts refer to v1 and the syntax seems to have changed from v1 to v2. I'm a bit lost as to how I can extend the base functionality in this way myself. Any help would be greatly appreciated.

This has been answered on a different question here: http://stackoverflow.com/a/41733045/852977 — Wes, Jan 19 '17 at 23:10

Wes · Accepted Answer · 2017-06-01T23:08:49.683

This should do the trick.
And Here is a fiddle of a plugin that will fill between any two datasets.

https://jsfiddle.net/ke5n5LnL/26/

Code:

<html>
    <div>
        <canvas id="myChart"></canvas>
    </div>
</html>


<script>

var fillBetweenLinesPlugin = {
    afterDatasetsDraw: function (chart) {
        var ctx = chart.chart.ctx;
        var xaxis = chart.scales['x-axis-0'];
        var yaxis = chart.scales['y-axis-0'];
        var datasets = chart.data.datasets;
        ctx.save();

        for (var d = 0; d < datasets.length; d++) {
            var dataset = datasets[d];
            if (dataset.fillBetweenSet == undefined) {
                continue;
            }

            // get meta for both data sets
            var meta1 = chart.getDatasetMeta(d);
            var meta2 = chart.getDatasetMeta(dataset.fillBetweenSet);

            ctx.beginPath();

            // vars for tracing
            var curr, prev;

            // trace set1 line
            for (var i = 0; i < meta1.data.length; i++) {
                curr = meta1.data[i];
                if (i === 0) {
                    ctx.moveTo(curr._view.x, curr._view.y);
                    ctx.lineTo(curr._view.x, curr._view.y);
                    prev = curr;
                    continue;
                }
                if (curr._view.steppedLine === true) {
                    ctx.lineTo(curr._view.x, prev._view.y);
                    ctx.lineTo(curr._view.x, curr._view.y);
                    prev = curr;
                    continue;
                }
                if (curr._view.tension === 0) {
                    ctx.lineTo(curr._view.x, curr._view.y);
                    prev = curr;
                    continue;
                }

                ctx.bezierCurveTo(
                  prev._view.controlPointNextX,
                  prev._view.controlPointNextY,
                  curr._view.controlPointPreviousX,
                  curr._view.controlPointPreviousY,
                  curr._view.x,
                  curr._view.y
                );
                prev = curr;
            }


            // connect set1 to set2 then BACKWORDS trace set2 line
            for (var i = meta2.data.length - 1; i >= 0; i--) {
                curr = meta2.data[i];
                if (i === meta2.data.length - 1) {
                    ctx.lineTo(curr._view.x, curr._view.y);
                    prev = curr;
                    continue;
                }
                if (curr._view.steppedLine === true) {
                    ctx.lineTo(prev._view.x, curr._view.y);
                    ctx.lineTo(curr._view.x, curr._view.y);
                    prev = curr;
                    continue;
                }
                if (curr._view.tension === 0) {
                    ctx.lineTo(curr._view.x, curr._view.y);
                    prev = curr;
                    continue;
                }

                // reverse bezier
                ctx.bezierCurveTo(
                  prev._view.controlPointPreviousX,
                  prev._view.controlPointPreviousY,
                  curr._view.controlPointNextX,
                  curr._view.controlPointNextY,
                  curr._view.x,
                  curr._view.y
                );
                prev = curr;
            }

            ctx.closePath();
            ctx.fillStyle = dataset.fillBetweenColor || "rgba(0,0,0,0.1)";
            ctx.fill();
        }
    } // end afterDatasetsDraw
}; // end fillBetweenLinesPlugin

Chart.pluginService.register(fillBetweenLinesPlugin);

function GenGraph(y) {
    // function to generate the graph with chart.js

    $(document).ready(function(){
    var roomCap = 220
    var prediction = [62, 65, 135, 145, 140, 120, 135, 189, 180, 175, 100, 25]
    var gndTruthUpper = [75, 100, 150, 175, 150, 150, 175, 200, 175, 150, 125, 100]
    var gndTruthLower = [50, 50, 75, 50, 25, 50, 75, 100, 125, 150, 125, 100, 75]

    var data = {
        labels: ["00", "05", "10", "15", "20", "25", "30", "35", "40", "45", "50", "55"],
            datasets: [{
                label: 'prediction',
                fill: false,
                pointRadius: 0,
                borderColor: 'blue',
                data: prediction
            },{
                label: 'GTUpper',
                fill: false,
                pointRadius: 0,
                borderDash: [10, 10],
                borderColor: 'black',
                data: gndTruthUpper,
                fillBetweenSet: 2,
                fillBetweenColor: 'rgba(0,0,0,0.1)'
           },{
                label: 'GTLower',
                fill: false,
                pointRadius: 0,
                borderDash: [10, 10],
                borderColor: 'black',
                data: gndTruthLower  
           }]
       };
       var options = {
           scales: {
               yAxes: [{
                   ticks: {
                       min: 0,
                       max: roomCap
                   }
               }]
           }
       };

       var ctx = document.getElementById("myChart").getContext("2d");
       var myChart = new Chart(ctx, {
           type: 'line',
           data: data,
           options: options
       });     
    });    
};

GenGraph();

</script>

also see https://stackoverflow.com/questions/41467923/chart-js-fill-between-two-lines/41733045#41733045 — Wes, Jun 01 '17 at 23:09

How to shade between 2 lines on a line graph using chart.js version2

1 Answers1