<canvas id="canvasInAPerfectWorld" width="490" height="220"></canvas>

<div id="canvasDiv"></div>

context = document.getElementById(‘canvasInAPerfectWorld‘).getContext("2d");

var canvasDiv = document.getElementById(‘canvasDiv‘);
canvas = document.createElement(‘canvas‘);
canvas.setAttribute(‘width‘, canvasWidth);
canvas.setAttribute(‘height‘, canvasHeight);
canvas.setAttribute(‘id‘, ‘canvas‘);
canvasDiv.appendChild(canvas);
if(typeof G_vmlCanvasManager != ‘undefined‘) {
	canvas = G_vmlCanvasManager.initElement(canvas);
}
context = canvas.getContext("2d");

$(‘#canvas‘).mousedown(function(e){
  var mouseX = e.pageX - this.offsetLeft;
  var mouseY = e.pageY - this.offsetTop;
 
  paint = true;
  addClick(e.pageX - this.offsetLeft, e.pageY - this.offsetTop);
  redraw();
});

$(‘#canvas‘).mousemove(function(e){
  if(paint){//是不是按下了鼠标
    addClick(e.pageX - this.offsetLeft, e.pageY - this.offsetTop, true);
    redraw();
  }
});

$(‘#canvas‘).mouseup(function(e){
  paint = false;
});

$(‘#canvas‘).mouseleave(function(e){
  paint = false;
});

var clickX = new Array();
var clickY = new Array();
var clickDrag = new Array();
var paint;
 
function addClick(x, y, dragging)
{
  clickX.push(x);
  clickY.push(y);
  clickDrag.push(dragging);
}

function redraw(){
  canvas.width = canvas.width; // Clears the canvas
 
  context.strokeStyle = "#df4b26";
  context.lineJoin = "round";
  context.lineWidth = 5;
 
  for(var i=0; i < clickX.length; i++)
  {
    context.beginPath();
    if(clickDrag[i] && i){//当是拖动而且i!=0时，从上一个点开始画线。
      context.moveTo(clickX[i-1], clickY[i-1]);
     }else{
       context.moveTo(clickX[i]-1, clickY[i]);
     }
     context.lineTo(clickX[i], clickY[i]);
     context.closePath();
     context.stroke();
  }
}