[Chartjs]-How to colorize individual rings in polar chart background in chart.js/ng2-charts?

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1👍

✅

This can be done by defining scale.gridLines.color option as an array of colors.

options: {
  scale: {
    gridLines: {
      color: [...]
    }
  }
}

Please take a look at the below runnable code and see how it works.

window.myChart = new Chart('canvas', {
  type: 'polarArea',
  data: {
    datasets: [{
      label: 'My Dataset',
      data: [4, 5, 4, 2, 6],
      backgroundColor: ['rgba(255, 159, 64, 0.2)', 'rgba(255, 205, 86, 0.2)', 'rgba(75, 192, 192, 0.2)', 'rgba(54, 162, 235, 0.2)', 'rgba(153, 102, 255, 0.2)']
    }]
  },
  options: {
    scale: {
      gridLines: {
        color: ['black', 'orange', 'yellow', 'green', 'blue']
      }
    }
  }
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.8.0/Chart.min.js"></script>   
<canvas id="canvas"></canvas>

1👍

This isn’t specifically an angular solution, but this video was very helpful if you’re looking to highlight only specific rings on the scale and I thought I’d share it for others with this same question: https://www.youtube.com/watch?v=hPGuSNdwOC4

I adapted it a bit to put lines at 100 and 110 on my chart (which represent 100% and 110% of budget) without knowing the number of ticks ahead of time as the video’s solution does. The ticks could change depending on the values of the charted numbers, chart size, etc. I use the r.ticks collection to get the number of ticks to properly calculate the circle radius.

const budgetLines = {
    id: "budgetLines",
    afterDatasetsDraw(chart, args, options) {
        var budgetTickCount = 0;
        var overBudgetTickCount = 0;
        const { ctx, chartArea: { top, bottom, left, right, width, height }, scales: { r } } = chart;
        const angle = Math.PI / 180;
        const trueHeight = r.yCenter - r.top;

        r.ticks.forEach(function (tick) {
            if (tick.value < options.budgetValue) {
                budgetTickCount = budgetTickCount + 1;
            }

            if (tick.value < options.budgetValue) {
                overBudgetTickCount = overBudgetTickCount + 1;
            }
        });

        const budgetRadius = ((trueHeight / r.end) * options.budgetValue) - (budgetTickCount + 1);
        const overBudgetRadius = ((trueHeight / r.end) * options.overBudgetValue) - (overBudgetTickCount + 1);

        ctx.save();
        ctx.beginPath();
        ctx.lineWidth = 1;
        ctx.strokeStyle = options.budgetColor;
        ctx.arc(r.xCenter, r.yCenter, budgetRadius, angle * 0, angle * 360, false);
        ctx.stroke();
        ctx.closePath();

        ctx.beginPath();
        ctx.lineWidth = 1;
        ctx.strokeStyle = options.overBudgetColor;
        ctx.arc(r.xCenter, r.yCenter, overBudgetRadius, angle * 0, angle * 360, false);
        ctx.stroke();
        ctx.closePath();
        ctx.restore();
    }
}

var ctx = document.getElementById("summaryChart");
new Chart(ctx, {
    type: "polarArea",
    data: chartData,
    options: {
        plugins: {
            budgetLines: {
                budgetValue: 100,
                overBudgetValue: 110,
                budgetColor: "rgba(0, 255, 0, 1)",
                overBudgetColor: "rgba(0, 0, 255, 1)"
            },
            legend: {
                display: false
            }
        },
        scales: {
            r: {
                suggestedMax: 100
            }
        }
    },
    plugins: [budgetLines]
});

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