如何在Charts.js中旋转饼图？

Question

It looks like a pie in charts.js is drawn by taking a vertical radius on the top half of the circle, and then moving clockwise from there. This works great most of the time, but for a pie with only 2 categories, it would be nice if it could be rotated so that the slice is centered, like this:

The rotation is calculated by taking the percentage of 360 and dividing by 2. (.14*360)/2 = 25.2 degrees left, so if I could just apply

transform: rotate(-25.2deg);

to the circle I would be good.

Since charts.js puts this on a canvas (as opposed to <svg> ) I don't know how to apply any transformations to this. Not sure if relevant, but here is my code for the chart:

HTML

<canvas id=canvas style='width:300px;height:300px;'></canvas>

JS

openRate = [
            {
                value: 488,
                color: "#FF9030",
                highlight: "rgba(255, 144, 48, 0.44)",
            },
            {
                value: 3475,
                color: "#008DB7",
                highlight: "rgba(0, 141, 183, 0.82)"
            }
        ];

var ctx=document.getElementById('canvas').getContext("2d");
var chart=new Chart(ctx).Pie(openRate);

And a fiddle: http://jsfiddle.net/msy6kf3a/

Answer 1

You Can use the

Rotation Options in chartjs

I'm using "Version: 2.1.6"

var options = {
   rotation: (-0.5 * Math.PI) - (25/180 * Math.PI)
}

var Chart = new Chart(ctx,{
  type: 'pie',
  data: data,
  options: options
});

Updated fiddle

Answer 2

You can rotate using CSS3: JSFIDDLE DEMO

#canvas{
   width:300px;
   height:300px; 
   -ms-transform: rotate(-25.2deg); /* IE 9 */
   -webkit-transform: rotate(-25.2deg); /* Chrome, Safari, Opera */
   transform: rotate(-25.2deg);
}