Chart.pluginService.register({
beforeDraw: function (chart) {
if (chart.config.options.elements.center) {
//Get ctx from string
var ctx = chart.chart.ctx;
//Get options from the center object in options
var centerConfig = chart.config.options.elements.center;
var fontStyle = centerConfig.fontStyle || 'Arial';
var txt = centerConfig.text;
var color = centerConfig.color || '#000';
var sidePadding = centerConfig.sidePadding || 20;
var sidePaddingCalculated = (sidePadding/100) * (chart.innerRadius * 2)
//Start with a base font of 30px
ctx.font = "30px " + fontStyle;
//Get the width of the string and also the width of the element minus 10 to give it 5px side padding
var stringWidth = ctx.measureText(txt).width;
var elementWidth = (chart.innerRadius * 2) - sidePaddingCalculated;
// Find out how much the font can grow in width.
var widthRatio = elementWidth / stringWidth;
var newFontSize = Math.floor(30 * widthRatio);
var elementHeight = (chart.innerRadius * 2);
// Pick a new font size so it will not be larger than the height of label.
var fontSizeToUse = Math.min(newFontSize, elementHeight);
//Set font settings to draw it correctly.
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.font = fontSizeToUse+"px " + fontStyle;
ctx.fillStyle = color;
//Draw text in center
ctx.fillText(txt, centerX, centerY);
}
}
});
use example
options: {
responsive: true,
legend: {
display: false
},
elements: {
center: {
text: '$'+(cost_vm+cost_storage+cost_data_management).toFixed(3),
color: '#FF6384', // Default is #000000
fontStyle: 'Arial', // Default is Arial
sidePadding: 20 // Defualt is 20 (as a percentage)
}
}
},
