HTML5 Canvas实现的一个画板

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可通过按钮改变画笔的颜色及大小,还可将画布保存为图片在下面进行显示。
<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<title>DEMO6:自定义画板</title>
</head>
<body>
<canvas id="canvas" width="600" height="300">
	浏览器不支持canvas   <!-- 如果不支持会显示这段文字 -->
</canvas>
<br/>
<button style="width:80px;background-color:yellow;" onclick='linecolor="yellow";'>YELLOW</button>
<button style="width:80px ;background-color:red;" onclick='linecolor="red";'>RED</button>
<button style="width:80px ;background-color:blue;" onclick='linecolor="blue";'>BLUE</button>
<button style="width:80px ;background-color:green;" onclick='linecolor="green";'>GREEN</button>
<button style="width:80px ;background-color:white;" onclick='linecolor="white";'>WHITE</button>
<button style="width:80px ;background-color:black;" onclick='linecolor="black";'>BLACK</button>
<br/>

<button style="width: 80px;background-color: white;" onclick="linw=4;">4PX</button>
<button style="width: 80px;background-color: white;" onclick="linw=8;">8PX</button>
<button style="width: 80px;background-color: white;" onclick="linw=16;">16PX</button>
<br/>

<button style="width: 80px;background-color: white;" onclick="copyimage();">EXPORT</button>

<br/>
<img src="" id="image_png" width="600px" height="300px">
<br/>

<script type="text/javascript">
	var canvas = document.getElementById('canvas');  //获取标签
	var ctx = canvas.getContext("2d");  

	var fillStyle = "black";
	ctx.fillRect(0,0,600,300);
	var onoff = false;  //按下标记
	var oldx = -10;
	var oldy = -10;
	//设置颜色
	var linecolor = "white";
	var linw = 4;
	canvas.addEventListener("mousemove",draw,true);  //鼠标移动事件
	canvas.addEventListener("mousedown",down,false);  //鼠标按下事件
	canvas.addEventListener("mouseup",up,false);  //鼠标弹起事件
	function down(event){
		onoff = true;
		oldx = event.pageX - 10;
		oldy = event.pageY - 10;
	}
	function up(){
		onoff = false;
	}
	function draw(event){
		if (onoff==true) {
			var newx = event.pageX - 10;
			var newy = event.pageY - 10
			ctx.beginPath();
			ctx.moveTo(oldx,oldy);
			ctx.lineTo(newx,newy);
			ctx.strokeStyle = linecolor;
			ctx.lineWidth = linw;
			ctx.lineCap = "round";
			ctx.stroke();

			oldx = newx;
			oldy = newy;
		}
	}
	function copyimage(event)
	{
		var img_png_src = canvas.toDataURL("image/png");  //将画板保存为图片格式的函数
		document.getElementById("image_png").src = img_png_src;
	}
	
	</script> 
</body>
</html>