用Javascript和canvas实现的涂鸦板，似乎不支持IE8及以下浏览器

蔚落 2022-08-08 03:20 191阅读 0赞

<!doctype html>  
<html>  
<head>  
 <meta content="text/html; charset=utf-8" http-equiv="Content-Type" />  
 <title>javascript canvas画图实例</title>  
 <meta http-equiv="X-UA-Compatible" content="IE=7" />  
 <meta name="keywords" content="" />  
 <meta name="description" content="" />  
 <style>  
 \*\{margin:0;padding:0;\}  
 .fa\{width:740px;margin:0 auto;\}  
 .top\{margin:20px 0;\}  
 .top input\{width:25px;height:25px;border:1px solid \#fff;border-radius:4px;background:\#ddd;\}  
 .top .i1\{background:\#000000;\}  
 .top .i2\{background:\#FF0000;\}  
 .top .i3\{background:\#80FF00;\}  
 .top .i4\{background:\#00FFFF;\}  
 .top .i5\{background:\#808080;\}  
 .top .i6\{background:\#FF8000;\}  
 .top .i7\{background:\#408080;\}  
 .top .i8\{background:\#8000FF;\}  
 .top .i9\{background:\#CCCC00;\}  
 \#canvas\{background:\#eee;cursor:default;\}  
 .font input\{font-size:14px;\}  
 .top .grea\{background:\#aaa;\}  
 </style>  
</head>  
<body>  
<div class="fa">  
    <div class="top">  
        <div id="color">  
            请选择画笔颜色：  
            <input class="i1" type="button" value="" />  
            <input class="i2" type="button" value="" />  
            <input class="i3" type="button" value="" />  
            <input class="i4" type="button" value="" />  
            <input class="i5" type="button" value="" />  
            <input class="i6" type="button" value="" />  
            <input class="i7" type="button" value="" />  
            <input class="i8" type="button" value="" />  
            <input class="i9" type="button" value="" />  
        </div>  
        <div class="font" id="font">  
            请选择画笔的宽度：  
            <input type="button" value="细" />  
            <input type="button" value="中" class="grea"/>  
            <input type="button" value="粗" />  
        </div>  
        <div>  
            <span id="error">如果有错误，请使用橡皮擦：</span>  
            <input id="eraser" style="width:60px;font-size:14px;"type="button" value="橡皮擦" />  
        </div>  
  <input id="clear" type="button" value="清除画布" style="width:80px;"/>  
  <input id="revocation" type="button" value="撤销" style="width:80px;"/>  
  <input id="imgurl" type="button" value="导出图片路径" style="width:80px;"/>  
    </div>  
    <canvas id="canvas" width="740" height="420">您的浏览器不支持 canvas 标签</canvas>  
    <div id="div1"></div>  
</div>  
<div id="html">  
  
</div>  
<script>  
(function()\{  
    var paint=\{  
        init:function()  
        \{  
            this.load();  
              
        \},  
        load:function()  
        \{     
            this.x=\[\];//记录鼠标移动是的X坐标  
            this.y=\[\];//记录鼠标移动是的Y坐标  
            this.clickDrag=\[\];  
            this.lock=false;//鼠标移动前，判断鼠标是否按下  
            this.isEraser=false;  
            //this.Timer=null;//橡皮擦启动计时器  
            //this.radius=5;  
            this.storageColor="\#000000";  
            this.eraserRadius=15;//擦除半径值  
            this.color=\["\#000000","\#FF0000","\#80FF00","\#00FFFF","\#808080","\#FF8000","\#408080","\#8000FF","\#CCCC00"\];//画笔颜色值  
            this.fontWeight=\[2,5,8\];  
            this.$=function(id)\{return typeof id=="string"?document.getElementById(id):id;\};  
            this.canvas=this.$("canvas");  
            if (this.canvas.getContext) \{  
            \} else \{  
                alert("您的浏览器不支持 canvas 标签");  
                return;  
            \}  
            this.cxt=this.canvas.getContext('2d');  
            this.cxt.lineJoin = "round";//context.lineJoin - 指定两条线段的连接方式  
            this.cxt.lineWidth = 5;//线条的宽度  
            this.iptClear=this.$("clear");  
            this.revocation=this.$("revocation");  
            this.imgurl=this.$("imgurl");//图片路径按钮  
            this.w=this.canvas.width;//取画布的宽  
            this.h=this.canvas.height;//取画布的高  
            this.touch =("createTouch" in document);//判定是否为手持设备  
            this.StartEvent = this.touch ? "touchstart" : "mousedown";//支持触摸式使用相应的事件替代  
         this.MoveEvent = this.touch ? "touchmove" : "mousemove";  
         this.EndEvent = this.touch ? "touchend" : "mouseup";  
         this.bind();  
        \},  
        bind:function()  
        \{  
            var t=this;  
            /\*清除画布\*/  
            this.iptClear.οnclick=function()  
            \{  
                t.clear();  
            \};  
            /\*鼠标按下事件，记录鼠标位置，并绘制，解锁lock，打开mousemove事件\*/  
            this.canvas\['on'+t.StartEvent\]=function(e)  
            \{     
                var touch=t.touch ? e.touches\[0\] : e;  
                var \_x=touch.clientX - touch.target.offsetLeft;//鼠标在画布上的x坐标，以画布左上角为起点  
                var \_y=touch.clientY - touch.target.offsetTop;//鼠标在画布上的y坐标，以画布左上角为起点               
                if(t.isEraser)  
                \{  
                /\*  
                    t.cxt.globalCompositeOperation = "destination-out";  
                    t.cxt.beginPath();  
                    t.cxt.arc(\_x, \_y,t.eraserRadius, 0, Math.PI \* 2);  
                    t.cxt.strokeStyle = "rgba(250,250,250,0)";  
                    t.cxt.fill();  
                    t.cxt.globalCompositeOperation = "source-over";  
                    \*/  
                    t.resetEraser(\_x,\_y,touch);  
                \}else  
                \{  
                    t.movePoint(\_x,\_y);//记录鼠标位置  
                    t.drawPoint();//绘制路线  
                \}  
                t.lock=true;  
            \};  
            /\*鼠标移动事件\*/  
            this.canvas\['on'+t.MoveEvent\]=function(e)  
            \{  
                var touch=t.touch ? e.touches\[0\] : e;  
                if(t.lock)//t.lock为true则执行  
                \{  
                    var \_x=touch.clientX - touch.target.offsetLeft;//鼠标在画布上的x坐标，以画布左上角为起点  
                    var \_y=touch.clientY - touch.target.offsetTop;//鼠标在画布上的y坐标，以画布左上角为起点  
                    if(t.isEraser)  
                    \{  
                        //if(t.Timer)clearInterval(t.Timer);  
                        //t.Timer=setInterval(function()\{  
                            t.resetEraser(\_x,\_y,touch);  
                        //\},10);  
                    \}  
                    else  
                    \{  
                        t.movePoint(\_x,\_y,true);//记录鼠标位置  
                        t.drawPoint();//绘制路线  
                    \}  
                \}  
            \};  
            this.canvas\['on'+t.EndEvent\]=function(e)  
            \{  
                /\*重置数据\*/  
                t.lock=false;  
                t.x=\[\];  
                t.y=\[\];  
                t.clickDrag=\[\];  
                clearInterval(t.Timer);  
                t.Timer=null;  
                  
            \};  
            this.revocation.οnclick=function()  
            \{  
                t.redraw();  
            \};  
            this.changeColor();  
            this.imgurl.οnclick=function()  
            \{  
                t.getUrl();  
            \};  
            /\*橡皮擦\*/  
            this.$("eraser").οnclick=function(e)  
         \{  
             t.isEraser=true;  
                t.$("error").style.color="red";  
                t.$("error").innerHTML="您已使用橡皮擦！";  
         \};  
        \},  
        movePoint:function(x,y,dragging)  
        \{     
            /\*将鼠标坐标添加到各自对应的数组里\*/  
            this.x.push(x);  
            this.y.push(y);  
            this.clickDrag.push(y);  
        \},  
        drawPoint:function(x,y,radius)  
        \{  
            for(var i=0; i < this.x.length; i++)//循环数组  
            \{     
                this.cxt.beginPath();//context.beginPath() , 准备绘制一条路径  
                  
                if(this.clickDrag\[i\] && i)\{//当是拖动而且i!=0时，从上一个点开始画线。  
                    this.cxt.moveTo(this.x\[i-1\], this.y\[i-1\]);//context.moveTo(x, y) , 新开一个路径，并指定路径的起点  
                \}else\{  
                    this.cxt.moveTo(this.x\[i\]-1, this.y\[i\]);  
                \}  
                this.cxt.lineTo(this.x\[i\], this.y\[i\]);//context.lineTo(x, y) , 将当前点与指定的点用一条笔直的路径连接起来  
                this.cxt.closePath();//context.closePath() , 如果当前路径是打开的则关闭它  
                this.cxt.stroke();//context.stroke() , 绘制当前路径  
            \}  
        \},  
        clear:function()  
        \{  
            this.cxt.clearRect(0, 0, this.w, this.h);//清除画布，左上角为起点  
        \},  
        redraw:function()  
        \{    
            /\*撤销\*/  
            this.cxt.restore();    
              
        \},    
        preventDefault:function(e)\{  
            /\*阻止默认\*/  
            var touch=this.touch ? e.touches\[0\] : e;  
      if(this.touch)touch.preventDefault();  
      else window.event.returnValue = false;  
     \},  
     changeColor:function()  
     \{  
         /\*为按钮添加事件\*/  
         var t=this,iptNum=this.$("color").getElementsByTagName("input"),fontIptNum=this.$("font").getElementsByTagName("input");  
         for(var i=0,l=iptNum.length;i<l;i++)  
         \{  
             iptNum\[i\].index=i;  
             iptNum\[i\].οnclick=function()  
             \{  
                 t.cxt.save();  
                 t.cxt.strokeStyle = t.color\[this.index\];  
                 t.storageColor=t.color\[this.index\];  
                 t.$("error").style.color="\#000";  
                 t.$("error").innerHTML="如果有错误，请使用橡皮擦：";  
                 t.cxt.strokeStyle = t.storageColor;  
                 t.isEraser=false;  
             \}  
         \}  
         for(var i=0,l=fontIptNum.length;i<l;i++)  
         \{  
             t.cxt.save();  
             fontIptNum\[i\].index=i;  
             fontIptNum\[i\].οnclick=function()  
             \{  
                 t.changeBackground(this.index);  
                 t.cxt.lineWidth = t.fontWeight\[this.index\];  
                 t.$("error").style.color="\#000";  
                 t.$("error").innerHTML="如果有错误，请使用橡皮擦：";  
                 t.isEraser=false;  
                 t.cxt.strokeStyle = t.storageColor;  
             \}  
         \}  
     \},  
     changeBackground:function(num)  
     \{  
         /\*添加画笔粗细的提示背景颜色切换，灰色为当前\*/  
         var fontIptNum=this.$("font").getElementsByTagName("input");  
         for(var j=0,m=fontIptNum.length;j<m;j++)  
            \{  
                fontIptNum\[j\].className="";  
                if(j==num) fontIptNum\[j\].className="grea";  
            \}  
     \},  
     getUrl:function()  
     \{  
           this.$("html").innerHTML=this.canvas.toDataURL();  
        \},  
        resetEraser:function(\_x,\_y,touch)  
     \{     
           
         /\*使用橡皮擦-提醒\*/  
         var t=this;  
            //this.cxt.lineWidth = 30;  
            /\*source-over 默认,相交部分由后绘制图形的填充(颜色,渐变,纹理)覆盖,全部浏览器通过\*/  
            t.cxt.globalCompositeOperation = "destination-out";  
            t.cxt.beginPath();  
            t.cxt.arc(\_x, \_y, t.eraserRadius, 0, Math.PI \* 2);  
            t.cxt.strokeStyle = "rgba(250,250,250,0)";  
            t.cxt.fill();  
            t.cxt.globalCompositeOperation = "source-over"  
     \}  
       
          
    \};  
    paint.init();  
\})();  
</script>  
</body>

</html>

转自:http://www.bcty365.com/content-62-6-1.html

据网上的说法是ie8不支持canvas, 在ie9和ie10才添加了对canvas的支持。有说法ie8能采用excanvas\_r3能模拟解决但效率不高，没试验出来。

此例子在firefox,Google Chrome,360浏览器里都能执行