var a, i, x1, y1, length =0;
var pi = Math.PI;
for (i=0; i != 2 * vertices ; i++){
this.beginPath();
this.moveTo(0,0);
a = i * (2 * pi/ (2*vertices) ) + startangle;
length = radius - depth * (i % 2);
x1 = length * Math.sin(a);
y1 = length * Math.cos(a);
this.lineTo( x1, y1);
a = (i +1)* (2 * pi/ (2*vertices) ) + startangle;
length = radius - depth * ((i +1)% 2);
x1 = length * Math.sin(a);
y1 = length * Math.cos(a);
this.lineTo( x1, y1);
this.closePath();
this.fillStyle= colors[i % 2];
this.fill();
this.strokeStyle =bordercolors[i % 2];
this.lineWidth = border;
this.stroke();
}