var canvas = document.getElementById('canvas');
if (canvas.getContext){
  var ctx = canvas.getContext('2d');

  //三次贝塞尔曲线
  ctx.beginPath();
  ctx.moveTo(75,40);
  ctx.bezierCurveTo(75,37,70,25,50,25);
  ctx.bezierCurveTo(20,25,20,62.5,20,62.5);
  ctx.bezierCurveTo(20,80,40,102,75,120);
  ctx.bezierCurveTo(110,102,130,80,130,62.5);
  ctx.bezierCurveTo(130,62.5,130,25,100,25);
  ctx.bezierCurveTo(85,25,75,37,75,40);
  ctx.fill();
}