How can I animate a pie chart part from 0 to 100% in svg?

Question

I am trying to figure out how to animate a pie chart part from 0 to 100. I can't even draw an arc that has more than 180 degrees. If I try to animate from a 1 degree angle to a 90 degree angle, instead of having a nice transition I'm getting a shape morph.

I'm trying to draw parts of the pie chart with paths like this:

M 100 100 l 0 -50 a 50 50 0 0 0 -20 10 z

My first challenge is calculating the last two numbers, the end point of the arc, and the second challenge is writing an animation that goes from a 1 deg angle to a 360 deg angle.

Any help would be greatly appreciated!

Answer 1

Its worth reading this answer on SO which has info on the dasharray effect which can be useful. That doesn't directly answer the pie question, but may give some ideas. A lot will depend on specifically how you want it animated, to whether these would work for you.

So you could draw a full circle with a string like "M 100, 100 m -75, 0 a 75,75 0 1,0 150,0 a 75,75 0 1,0 -150,0" which draws 2 arcs.

You could also just do it with a circle. So here's a few bits, and a Snap example alongside it, as you will be using that, and its useful to compare...

<svg width="600" height="425">
    <path d="M 100, 100 m -75, 0 a 75,75 0 1,0 150,0 a 75,75 0 1,0 -150,0" fill="none" stroke="black" stroke-width="150" stroke-dasharray="0 600 600 0" stroke-dashoffset="1000">
        <animate attributeType="XML" attributeName="stroke-dashoffset" from="0" to="600" dur="2s" repeatCount="1" fill="freeze"/> 
    </path>
    <circle cx="150" cy="350" r="80" fill="none" stroke="red" stroke-width="161" stroke-dasharray="0 600 600 0" stroke-dashoffset="1000" >
        <animate attributeType="XML" attributeName="stroke-dashoffset" from="0" to="600" dur="2s" repeatCount="1" fill="freeze">
        </animate>
    </circle>
</svg>

same last bit with Snap.js

var s = Snap(600,600);

var c = s.circle(150, 150, 80).attr({
    fill: "none",
    stroke: 'red',
    strokeWidth: 161,
    strokeDasharray: "0 600 600 0",
    strokeDashoffset: 1000
});

Snap.animate(0,600, function( value ){ 
       c.attr({ 'strokeDashoffset': value })
},5000 );

Here is a jsfiddle with them all on