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canvas绘图的强大功能，让人前仆后继的去研究它。代码全部加起来不足百行。还用到了h5中的<input type="color"/>和<input type="range"/>
使得页面更加简洁。
本文只用了鼠标的三个事件 onmousedown onmousemove onmouseup就轻松实现了网页画板的制作。
上代码：
1 <!DOCTYPE html> 2 <html> 3 <head lang="en"> 4 <meta charset="UTF-8"> 5 <title></title> 6 <style type="text/css"> 7 #canvas{ 8 border: 1px solid #333; 9 display: block; 10 margin:20px auto; 11 } 12 #color{ 13 width:100px; 14 height:32px; 15 position:absolute; 16 right:115px; 17 top:200px; 18 } 19 #range{ 20 width:100px; 21 height:32px; 22 position:absolute; 23 right:115px; 24 top:125px; 25 } 26 #demo{ 27 background:black; 28 width:100px; 29 height:5px; 30 position:absolute; 31 right:115px; 32 top:100px; 33 } 34 </style> 35 </head> 36 <body background-color="rgba(0,0,0,0.5)"> 37 <div class="box"> 38 <h3 align="center">CANVAS制作简单在线画板</h3> 39 <canvas id="canvas" width="800" height="600"></canvas> 40 <input type="color" id="color"/> 41 <div id="demo"></div> 42 <input type="range" id="range" min="1" max="10"/> 43 </div> 44 <script type="text/javascript"> 45 var canvas=document.getElementById("canvas"); 46 var cxt=canvas.getContext("2d"); 47 var color=document.getElementById("color"); 48 var size=document.getElementById("range"); 49 var demo=document.getElementById("demo"); 50 //根据size的变化来使得size上面的线条演示画笔粗细。 51 size.onchange=function(){ 52 demo.style.height=size.value+"px"; 53 } 54 //使得color的颜色与演示线条的颜色一致 55 color.onchange=function(){ 56 demo.style.background=color.value; 57 } 58 var flag=false; 59 //鼠标按下 60 canvas.onmousedown= function (e) { 61 var mouseX= e.pageX-this.offsetLeft; 62 var mouseY= e.pageY-this.offsetTop; 63 flag=true; 64 cxt.beginPath(); 65 cxt.lineWidth=size.value; 66 cxt.strokeStyle=color.value; 67 cxt.moveTo(mouseX,mouseY); 68 }; 69 //鼠标移动 70 canvas.onmousemove= function (e) { 71 var mouseX= e.pageX-this.offsetLeft; 72 var mouseY= e.pageY-this.offsetTop; 73 if(flag){ 74 75 cxt.lineTo(mouseX,mouseY); 76 cxt.stroke(); 77 } 78 } 79 //鼠标松开 80 canvas.onmouseup= function (e) { 81 flag=false; 82 } 83 </script> 84 </body> 85 </html>
大家做成后的木模样
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原文地址：http://www.cnblogs.com/pjdsy/p/4681492.html
