drawing centered arcs in raphael js

Question

I need to draw concentric arcs of various sizes using raphael.js. I tried to understand the code behind http://raphaeljs.com/polar-clock.html, which is very similar to what I want, but, whithout comments, it is quite difficult to fathom.

Ideally, I would need a function that creates a path that is at a given distance from some center point, starts at some angle and ends at some other angle.

Answer 1

You can also do this without having to use loops. The following achieves this and works with negative angles as well.

Pass in a Raphael object as r. The angles start with 0 degrees, which is the top of the circle rather than the right as was listed in a couple of other solutions.

        function drawArc(r, centerX, centerY, radius, startAngle, endAngle) {
            var startX = centerX+radius*Math.cos((90-startAngle)*Math.PI/180); 
            var startY = centerY-radius*Math.sin((90-startAngle)*Math.PI/180);
            var endX = centerX+radius*Math.cos((90-endAngle)*Math.PI/180); 
            var endY = centerY-radius*Math.sin((90-endAngle)*Math.PI/180);
            var flg1 = 0;

            if (startAngle>endAngle)
                flg1 = 1;
            else if (startAngle<180 && endAngle<180)
                flg1 = 0;
            else if (startAngle>180 && endAngle>180)
                flg1 = 0;
            else if (startAngle<180 && endAngle>180)
                flg1 = 0; // edited for bugfix here, previously this was 1
            else if (startAngle>180 && endAngle<180)
                flg1 = 1;

            return r.path([['M',startX, startY],['A',radius,radius,0,flg1,1,endX,endY]]);
        };