HTMLキャンバス上で線幅が連続的に変化する線を描画する

var context = document.getElementById('canvas1').getContext('2d');
var pts = [null, null, null, null];
for(var i=-1; i<25; i=i+1)
{
   var width = 0.5+i/2;
   var m = 200;
   var x = Math.cos(i/4) * 180;
   var y = Math.sin(i/4) * 140;
   
   pts[0] = pts[1];
   pts[1] = pts[2];
   pts[2] = { X:x, Y:y};
   
   if(pts[0] == null)
   continue;
   var p0 = pts[0];
   var p1 = pts[1];
   var p2 = pts[2];
   var x0 = (p0.X + p1.X) / 2;
   var y0 = (p0.Y + p1.Y) / 2;
   var x1 = (p1.X + p2.X) / 2;
   var y1 = (p1.Y + p2.Y) / 2;
   
   context.beginPath();
   context.lineWidth = width;
   context.strokeStyle = "blue";
   context.moveTo(m+x0, m+y0);
   context.quadraticCurveTo(m+p1.X, m+p1.Y, m+x1, m+y1);
   context.stroke();
}