javascript: piechart.js

function Sector(x, y, radius, startAngle, endAngle) {
  SpecialAttrPath.call(this, {
    radius: 0,
    startAngle: startAngle,
    endAngle: endAngle
  });
  this.attr({
    x: x,
    y: y,
    radius: radius,
    startAngle: startAngle,
    endAngle: endAngle
  });
}

Sector.prototype = Object.create(SpecialAttrPath.prototype);
Sector.prototype._make = function() {

  var attr = this._attributes,
      radius = attr.radius,
      startAngle = attr.startAngle,
      endAngle = attr.endAngle;

  var startX, startY, endX, endY;
  var diffAngle = Math.abs(endAngle - startAngle);

  this.startX = startX = radius * Math.cos(startAngle);
  this.startY = startY = radius * Math.sin(startAngle);
  if (diffAngle < Math.PI*2) {
    endX = radius * Math.cos(endAngle);
    endY = radius * Math.sin(endAngle);
  } else { // angles differ by more than 2*PI: draw a full circle
    endX = startX;
    endY = startY - .0001;
  }

  this.endX = endX;
  this.endY = endY;

  this.radiusExtentX = radius * Math.cos(startAngle + (endAngle - startAngle)/2);
  this.radiusExtentY = radius * Math.sin(startAngle + (endAngle - startAngle)/2);

  return this.moveTo(0, 0)
    .lineTo(startX, startY)
    .arcTo(radius, radius, 0, (diffAngle < Math.PI) ? 0 : 1, 1, endX, endY)
    .lineTo(0, 0);

};