复习canvas

今天，项目中用到html5中的canvas，以前，在网上找到一个canvas画板的例子，以下是例子的代码：

var canvas = document.getElementsByTagName('canvas')[0]; 
var context = canvas.getContext('2d'); 
 
var linex = new Array();  
var liney = new Array();  
var linen = new Array(); 
var defaultColor='#000';
var size=0;

var lastX = -1;  
var lastY = -1;  
var hue = 0;  
var flag = 0;  
function touchStart(e) {
	e.preventDefault();
	var touches = e.changedTouches,
		i = 0, l = touches.length, touch;
	for (; i < l; i++) {
		touch = touches[i];
		flag = 1;    //代表鼠标是否按下 1 按下 0释放
		size=linex.length;
		linex.push(touch.pageX-$("#canv").offset().left);  
		liney.push(touch.pageY-$("#canv").offset().top);  
		linen.push(0);  

	}
}

function touchMove(e) {
	e.preventDefault();
	var touches = e.targetTouches,
		i = 0, l = touches.length, touch;
	for (; i < l; i++) {
		touch = touches[i];
   if (flag == 1) {  
   linex.push(touch.pageX-$("#canv").offset().left);  
   liney.push(touch.pageY-$("#canv").offset().top);  
   linen.push(1);  
   context.save();  
   
   context.translate(context.canvas.width/2, context.canvas.height/2);  
   context.translate(-context.canvas.width/2, -context.canvas.height/2);  
   context.beginPath();  
   context.lineWidth = 5 + Math.random() * 10;  

   for (var i=size;i<linex.length;i++) {  
		 lastX = linex[i];  
		 lastY = liney[i];  
		 if (linen[i] == 0) {  
			context.moveTo(lastX,lastY);  
		 } else {  
			context.lineTo(lastX,lastY);  
		 }  
   }  

   context.strokeStyle = defaultColor;  
   context.shadowColor = 'white';  
   context.shadowBlur = 5;  
   context.stroke();  
  // context.restore();  
}  
	}

}

function touchEnd(e) {
	var touches = e.changedTouches,
		i = 0, l = touches.length, touch;
	for (;i < l; i++) {
		touch = touches[i];
		flag = 0;  
		linex.push(touch.pageX-$("#canv").offset().left);  
		liney.push(touch.pageY-$("#canv").offset().top);  
		linen.push(0);
	}

}

canvas.addEventListener("touchstart", touchStart, false);
canvas.addEventListener("touchmove", touchMove, false);
canvas.addEventListener("touchend", touchEnd, false);

这个例子实现了以前的项目需求，但一直以来，对其不是很理解。今天重新翻出来，实现新的项目需求，再次看的时候，感觉很轻松，一看就很明了。进而感觉canvas这不错，很好玩，也不是很难。在网上，找了些教程，基本的，看看都很容易理解。在画板中，清楚里面画得痕迹，可以通过context.clearRect ( 0 , 0 , canvas.width , canvas.height )来实现。其他的感觉没有可讲，自己认真想想，慢慢体会，可能印象会更加深刻。