SVG donut slice as path element (annular sector)

Demo: http://phrogz.net/svg/procedural_annular_sector.xhtml

Usage:

annularSector( myPathElement, {
  centerX:100, centerY:150,
  startDegrees:190, endDegrees:230,
  innerRadius:75, outerRadius:100
});

Core function:

// Options:
// - centerX, centerY: coordinates for the center of the circle    
// - startDegrees, endDegrees: fill between these angles, clockwise
// - innerRadius, outerRadius: distance from the center
// - thickness: distance between innerRadius and outerRadius
//   You should only specify two out of three of the radii and thickness
function annularSector(path,options){
  var opts = optionsWithDefaults(options);
  var p = [ // points
    [opts.cx + opts.r2*Math.cos(opts.startRadians),
     opts.cy + opts.r2*Math.sin(opts.startRadians)],
    [opts.cx + opts.r2*Math.cos(opts.closeRadians),
     opts.cy + opts.r2*Math.sin(opts.closeRadians)],
    [opts.cx + opts.r1*Math.cos(opts.closeRadians),
     opts.cy + opts.r1*Math.sin(opts.closeRadians)],
    [opts.cx + opts.r1*Math.cos(opts.startRadians),
     opts.cy + opts.r1*Math.sin(opts.startRadians)],
  ];

  var angleDiff = opts.closeRadians - opts.startRadians;
  var largeArc = (angleDiff % (Math.PI*2)) > Math.PI ? 1 : 0;
  var cmds = [];
  cmds.push("M"+p[0].join());                                // Move to P0
  cmds.push("A"+[opts.r2,opts.r2,0,largeArc,1,p[1]].join()); // Arc to  P1
  cmds.push("L"+p[2].join());                                // Line to P2
  cmds.push("A"+[opts.r1,opts.r1,0,largeArc,0,p[3]].join()); // Arc to  P3
  cmds.push("z");                                // Close path (Line to P0)
  path.setAttribute('d',cmds.join(' '));

  function optionsWithDefaults(o){
    // Create a new object so that we don't mutate the original
    var o2 = {
      cx           : o.centerX || 0,
      cy           : o.centerY || 0,
      startRadians : (o.startDegrees || 0) * Math.PI/180,
      closeRadians : (o.endDegrees   || 0) * Math.PI/180,
    };

    var t = o.thickness!==undefined ? o.thickness : 100;
    if (o.innerRadius!==undefined)      o2.r1 = o.innerRadius;
    else if (o.outerRadius!==undefined) o2.r1 = o.outerRadius - t;
    else                                o2.r1 = 200           - t;
    if (o.outerRadius!==undefined)      o2.r2 = o.outerRadius;
    else                                o2.r2 = o2.r1         + t;

    if (o2.r1<0) o2.r1 = 0;
    if (o2.r2<0) o2.r2 = 0;

    return o2;
  }
}