js通过canvas实现画笔功能手记

<script src="http://www.gxlcms.com/static/home/js/jquery.min.js"></script>
<canvas id="paintcanvas" width="600" height="700"></canvas>
<script>
var paint;
var clickX=[];
var clickY=[];
var clickDrag=[];
function addClick(x,y,dragging)
{
 clickX.push(x);
 clickY.push(y);
 clickDrag.push(dragging);
}
function redraw()
{
 paintcanvas.strokeStyle = "#df4b26";
 paintcanvas.lineJoin = "round";
 paintcanvas.lineWidth = 5;
 for(var i=0; i < clickX.length; i++)
 {
 paintcanvas.beginPath();
 if(clickDrag[i] && i){//当是拖动而且i!=0时，从上一个点开始画线。
 paintcanvas.moveTo(clickX[i-1], clickY[i-1]);
 }else{
 paintcanvas.moveTo(clickX[i]-1, clickY[i]);
 }
 paintcanvas.lineTo(clickX[i], clickY[i]);
 paintcanvas.closePath();
 paintcanvas.stroke();
 }
}
paintcanvas=$('#paintcanvas')[0].getContext("2d");
$('#paintcanvas').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();
});
$('#paintcanvas').mousemove(function(e){
 if(paint){
 addClick(e.pageX-this.offsetLeft,e.pageY-this.offsetTop,true);
 redraw();
 }
});
$('#paintcanvas').mouseup(function(e){
 paint = false;
});
$('#paintcanvas').mouseleave(function(e){
 paint = false;
});
</script>