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" style="max-width:90%" height="300px" alt="HTML5 Canvas實作的一個畫板" >
<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>
