ChartJS Doughnut Charts Gradient Fill

Question

So I tried to make a gradient fill for the ChartJS doughnut chart, but this only works horizontal and not in a circle.

This is the code that I'm using:

   var ctx = document.getElementById("chart-area").getContext("2d");

   var gradient1 = ctx.createLinearGradient(0, 0, 0, 175);
   gradient1.addColorStop(0.0, '#ACE1DB');
   gradient1.addColorStop(1.0, '#7FBDB9');


   var gradient2 = ctx.createLinearGradient(0, 0, 400, 400);
   gradient2.addColorStop(0, '#B5D57B');
   gradient2.addColorStop(1, '#98AF6E');

   var gradient3 = ctx.createLinearGradient(0, 0, 0, 175);
   gradient3.addColorStop(0, '#E36392');
   gradient3.addColorStop(1, '#FE92BD');

   var gradient4 = ctx.createLinearGradient(0, 0, 0, 175);
   gradient4.addColorStop(1, '#FAD35E');
   gradient4.addColorStop(0, '#F4AD4F');

   /* ADD DATA TO THE DOUGHNUT CHART */
   var doughnutData = [
    {
      value: 80,
      color: gradient1,
      highlight: "#E6E6E6",
      label: "NUTRIENTS"
    },
    {
      value: 20,
      color:"#E6F1EE"

    },
    {
      value:50,
      color: gradient2,
      highlight: "#E6E6E6",
      label: "PROTEINE"
    },
    {
      value: 50,
      color:"#E6F1EE"
    },
    {
      value: 75,
      color: gradient3,
      highlight: "#E6E6E6",
      label: "FETTE"
    },
    {
      value:25,
      color:"#E6F1EE"
    },
    {
      value: 77,
      color: gradient4,
      highlight: "#E6E6E6",
      label: "CARBS"
    }
    {
      value: 23,
      color:"#E6F1EE"
    },
   ];

Is it possible to implement the gradient on a radius, as seen on this design?

Thanks!

Answer 1

ChartJS will not (properly) use gradient fill colors when drawing a linear gradient on non-linear paths like your donut chart. A linear gradient does not curve.

Possibility #1 -- use a radial gradient

You might experiment with a radial gradient and see if the results meets your design needs.

Possibility #2 -- use a gradient stroke (a DIY project)

Also, canvas's stroke will curve around a circle.

If you want to "roll-your-own" gradient donut chart, here's example code and a Demo that uses a gradient strokeStyle on a circular path (see my previous answer here: Angle gradient in canvas):

var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");

function drawMultiRadiantCircle(xc, yc, r, radientColors) {
  var partLength = (2 * Math.PI) / radientColors.length;
  var start = 0;
  var gradient = null;
  var startColor = null,
      endColor = null;

  for (var i = 0; i < radientColors.length; i++) {
    startColor = radientColors[i];
    endColor = radientColors[(i + 1) % radientColors.length];

    // x start / end of the next arc to draw
    var xStart = xc + Math.cos(start) * r;
    var xEnd = xc + Math.cos(start + partLength) * r;
    // y start / end of the next arc to draw
    var yStart = yc + Math.sin(start) * r;
    var yEnd = yc + Math.sin(start + partLength) * r;

    ctx.beginPath();

    gradient = ctx.createLinearGradient(xStart, yStart, xEnd, yEnd);
    gradient.addColorStop(0, startColor);
    gradient.addColorStop(1.0, endColor);

    ctx.strokeStyle = gradient;
    ctx.arc(xc, yc, r, start, start + partLength);
    ctx.lineWidth = 30;
    ctx.stroke();
    ctx.closePath();

    start += partLength;
  }
}

var someColors = [];
someColors.push('#0F0');
someColors.push('#0FF');
someColors.push('#F00');
someColors.push('#FF0');
someColors.push('#F0F');

drawMultiRadiantCircle(150, 150, 120, someColors);

body{ background-color: ivory; }
#canvas{border:1px solid red;}

<canvas id="canvas" width=300 height=300></canvas>

Answer 2

yes What I did on my end is this.

Step 1 - Grab your chart.

  @ViewChild('slideDoughnutChart') slideDoughnutChart: BaseChartDirective;

Step 2 - Declare a const gradient and assign it.

const gradient = this.slideDoughnutChart.chart.ctx.createLinearGradient(0, 0, 0, 220);

Step 3 - Push the colors that you wan to see as Gradient.

const colors = [];
for (let i = 0; i < 4; i++) {
  gradient.addColorStop(0, 'rgb(37, 77, 180)');
  gradient.addColorStop(1, 'rgb(123, 98, 221)');
  colors.push(gradient);
}

Here I have pushed the same color.

Step 4 - Set doughnut chart colors variable to colors array.

this.slideDoughnutChartColors = [{ backgroundColor: colors }];

Step 5 - Assign slideDoughnutChartColors variable to colors binding in canvas.

<canvas class="chartjs canvasResponsive" baseChart #slideDoughnutChart="base-chart" [colors]="slideDoughnutChartColors" ></canvas>

If you follow the steps correctly, You will end with this.

For 4 different colors you need to create 4 different variables. For example something like this.

const gradientOne = this.slideDoughnutChart.chart.ctx.createLinearGradient(0, 0, 0, 400);
const gradientTwo = this.slideDoughnutChart.chart.ctx.createLinearGradient(0, 0, 100, 400);
const gradientThree = this.slideDoughnutChart.chart.ctx.createLinearGradient(0, 0, 0, 400);
const gradientFour = this.slideDoughnutChart.chart.ctx.createLinearGradient(0, 0, 0, 400);

then doing something like this.

 for (let i = 0; i < this.slideDoughnutChartData.length; i++) {
      switch (i) {
        case 0:
          gradientOne.addColorStop(0, 'rgb(223, 43, 100)');
          gradientOne.addColorStop(1, 'rgb(224, 105, 84)');
          colors.push(gradientOne);
          break;
        case 1:
          gradientTwo.addColorStop(0, 'rgb(248, 188, 80)');
          gradientTwo.addColorStop(1, 'rgb(243, 217, 53)');
          colors.push(gradientTwo);
          break;
        case 2:
          gradientThree.addColorStop(0, 'rgb(147, 229, 151)');
          gradientThree.addColorStop(1, 'rgb(3, 220, 179)');
          colors.push(gradientThree);
          break;
        case 3:
          gradientFour.addColorStop(0, 'rgb(123, 98, 221)');
          gradientFour.addColorStop(1, 'rgb(37, 77, 180)');
          colors.push(gradientFour);
          break;
      }
    }

will end you up with.

This is my data for the chart.

this.slideDoughnutChartData = [25, 35, 20, 25, 2];