Chart.js Doughnut with rounded edges and text centered

I've added a piece of code to change the center text when legend is clicked.

afterDraw: function (chart) {
    if (chart.center) {
        var ctx = chart.chart.ctx;

        var i,a,s;
        var n = chart;
        var total = 0;
        for(i=0,a=(n.data.datasets||[]).length;a>i;++i){
            s = n.getDatasetMeta(i);
            var x;
            for(x=0; x<s.data.length; x++){
                if (!s.data[x].hidden)
                    total += n.data.datasets[i].data[x];
            }
        }

        ctx.save();
        ctx.font = chart.center.font;
        ctx.fillStyle = chart.center.fillStyle;
        ctx.textAlign = 'center';
        ctx.textBaseline = 'middle';
        var centerX = (chart.chartArea.left + chart.chartArea.right) / 2;
        var centerY = (chart.chartArea.top + chart.chartArea.bottom) / 2;
        ctx.fillText(total, centerX, centerY);
        ctx.restore();
    }
}

Fiddle - http://jsfiddle.net/cd3fdoy9/49/

With v2.1.3, you can use the pluginService to do this

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Preview

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Script

// round corners
Chart.pluginService.register({
    afterUpdate: function (chart) {
        if (chart.config.options.elements.arc.roundedCornersFor !== undefined) {
            var arc = chart.getDatasetMeta(0).data[chart.config.options.elements.arc.roundedCornersFor];
            arc.round = {
                x: (chart.chartArea.left + chart.chartArea.right) / 2,
                y: (chart.chartArea.top + chart.chartArea.bottom) / 2,
                radius: (chart.outerRadius + chart.innerRadius) / 2,
                thickness: (chart.outerRadius - chart.innerRadius) / 2 - 1,
                backgroundColor: arc._model.backgroundColor
            }
        }
    },

    afterDraw: function (chart) {
        if (chart.config.options.elements.arc.roundedCornersFor !== undefined) {
            var ctx = chart.chart.ctx;
            var arc = chart.getDatasetMeta(0).data[chart.config.options.elements.arc.roundedCornersFor];
            var startAngle = Math.PI / 2 - arc._view.startAngle;
            var endAngle = Math.PI / 2 - arc._view.endAngle;

            ctx.save();
            ctx.translate(arc.round.x, arc.round.y);
            console.log(arc.round.startAngle)
            ctx.fillStyle = arc.round.backgroundColor;
            ctx.beginPath();
            ctx.arc(arc.round.radius * Math.sin(startAngle), arc.round.radius * Math.cos(startAngle), arc.round.thickness, 0, 2 * Math.PI);
            ctx.arc(arc.round.radius * Math.sin(endAngle), arc.round.radius * Math.cos(endAngle), arc.round.thickness, 0, 2 * Math.PI);
            ctx.closePath();
            ctx.fill();
            ctx.restore();
        }
    },
});

// write text plugin
Chart.pluginService.register({
    afterUpdate: function (chart) {
        if (chart.config.options.elements.center) {
            var helpers = Chart.helpers;
            var centerConfig = chart.config.options.elements.center;
            var globalConfig = Chart.defaults.global;
            var ctx = chart.chart.ctx;

            var fontStyle = helpers.getValueOrDefault(centerConfig.fontStyle, globalConfig.defaultFontStyle);
            var fontFamily = helpers.getValueOrDefault(centerConfig.fontFamily, globalConfig.defaultFontFamily);

            if (centerConfig.fontSize)
                var fontSize = centerConfig.fontSize;
                // figure out the best font size, if one is not specified
            else {
                ctx.save();
                var fontSize = helpers.getValueOrDefault(centerConfig.minFontSize, 1);
                var maxFontSize = helpers.getValueOrDefault(centerConfig.maxFontSize, 256);
                var maxText = helpers.getValueOrDefault(centerConfig.maxText, centerConfig.text);

                do {
                    ctx.font = helpers.fontString(fontSize, fontStyle, fontFamily);
                    var textWidth = ctx.measureText(maxText).width;

                    // check if it fits, is within configured limits and that we are not simply toggling back and forth
                    if (textWidth < chart.innerRadius * 2 && fontSize < maxFontSize)
                        fontSize += 1;
                    else {
                        // reverse last step
                        fontSize -= 1;
                        break;
                    }
                } while (true)
                ctx.restore();
            }

            // save properties
            chart.center = {
                font: helpers.fontString(fontSize, fontStyle, fontFamily),
                fillStyle: helpers.getValueOrDefault(centerConfig.fontColor, globalConfig.defaultFontColor)
            };
        }
    },
    afterDraw: function (chart) {
        if (chart.center) {
            var centerConfig = chart.config.options.elements.center;
            var ctx = chart.chart.ctx;

            ctx.save();
            ctx.font = chart.center.font;
            ctx.fillStyle = chart.center.fillStyle;
            ctx.textAlign = 'center';
            ctx.textBaseline = 'middle';
            var centerX = (chart.chartArea.left + chart.chartArea.right) / 2;
            var centerY = (chart.chartArea.top + chart.chartArea.bottom) / 2;
            ctx.fillText(centerConfig.text, centerX, centerY);
            ctx.restore();
        }
    },
})

and then

    ...
    options: {
        elements: {
            arc: {
                roundedCornersFor: 0
            },
            center: {
                // the longest text that could appear in the center
                maxText: '100%',
                text: '67%',
                fontColor: '#FF6684',
                fontFamily: "'Helvetica Neue', 'Helvetica', 'Arial', sans-serif",
                fontStyle: 'normal',
                // fontSize: 12,
                // if a fontSize is NOT specified, we will scale (within the below limits) maxText to take up the maximum space in the center
                // if these are not specified either, we default to 1 and 256
                minFontSize: 1,
                maxFontSize: 256,
            }
        }
    }
};

You can get rid of a bit of code if you don't want it to be generic (eg. if you fix the fontSize, if you fix the index to round, etc.)

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Fiddle - http://jsfiddle.net/cd3fdoy9/