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Detailed explanation of HTML5 implementation of partial image magnifying glass (adjustable) (graphics and text)

黄舟Original: 2017-03-25 15:42:063992browse

The following continues to introduce ## based on html5canvascanvas #Magnifying glass effect:

Main steps:

1) Loading of images, there is www.php.cn/html5-tutorial-358646.html in the previous blog, you must pay attention to apache configuration, otherwise getImageData() will have security issues and cannot run!

##2) Core: Mapping between two image matrices,

Set o as the center of the circle, then transform The last point A' corresponds to point A of the original image (this is the effect of magnification!!! In this experiment, the magnification factor is 2)

3) For the sake of simplicity, the linear interpolation method is not used, directly Round to get the coordinates of point A.

for (var j=0;j<image.height;j++){
	     for(var i=0;i<image.width;i++){
		   var k=4*(image.width*j+i);
		   var k1=4*(image.width*Math.floor((j+y0)/2)+Math.floor((i+x0)/2));
                   ...
                    else if(isIn(x0,y0,i,j,r)){//isIn()判定点是否在园内
			  if(k1>=0&&k1<=4*image.height*image.width){
		      imagedata2.data[k+0]=imagedata1.data[k1+0];
			  imagedata2.data[k+1]=imagedata1.data[k1+1];
			  imagedata2.data[k+2]=imagedata1.data[k1+2];
			  imagedata2.data[k+3]=255;
			 // console.log(&#39;x:&#39;+x+&#39;y:&#39;+y);
	      }

4) In order to make the mirror stand out, set the point at the edge to a black point (that is, rgb is 0)

	function isOn(x0,y0,x,y,r){//放大镜边缘
	    if((x0-x)*(x0-x)+(y0-y)*(y0-y)==r*r)
		  return true;
		else
		  return false;
	}

	       if (isOn(x0,y0,i,j,r)){
		      imagedata2.data[k+0]=0;
			  imagedata2.data[k+1]=0;
			  imagedata2.data[k+2]=0;
			  imagedata2.data[k+3]=255;
			  }

5) Out of bounds or wrap. point (if it exists), ignore it (just take the original value)

		  else{
		      imagedata2.data[k+0]=imagedata1.data[k+0];
			  imagedata2.data[k+1]=imagedata1.data[k+1];
			  imagedata2.data[k+2]=imagedata1.data[k+2];
			  imagedata2.data[k+3]=255;
		  }

6) External setting of the magnifying glass radius

Also use canvas and onclick functions, as shown below:

<canvas id="bar" height="30" width="305"></canvas>
&nbsp放大镜半径为<span id=&#39;r&#39;></span>
<script>
var canvas2=document.getElementById(&#39;bar&#39;);
var context2=canvas2.getContext(&#39;2d&#39;);
context2.beginPath();
context2.lineWidth = 1;//边框宽度                           
context2.strokeStyle = "#ff00ff";//边框颜色
context2.strokeRect(10,0,295,28);//边框坐标及大小
context2.closePath();
canvas2.onclick=function(e){
     var x1=e.clientX-e.target.offsetLeft;
     context2.clearRect(0,0,305,30);//擦除上次的痕迹
     context2.beginPath();
     context2.lineWidth = 1;//边框宽度                           
     context2.strokeStyle = "#ff00ff";//边框颜色
     context2.strokeRect(10,0,295,28);//边框坐标及大小
     context2.fillStyle = "#00ff00";//填充canvas的背景颜色
     context2.fillRect(0, 0, x1,28);//参数分别表示 x轴,y轴,宽度,高度
     document.getElementById(&#39;r&#39;).innerHTML=Math.floor(x1/6);
     r=Math.floor(x1/6);
}
</script>

The following is the complete code:

<!DOCTYPE html>   
<html>
<head>   
<title>canvas图像处理</title>  
</head>  
<body>  
<h1>canvas放大镜</h1>  
<canvas  id="canvas1" width="600" height="450">是时候更换浏览器了<a href="http://firefox.com.cn/download/">点击下载firefox</a></canvas> 
<!--当浏览器不支持html5时，会显示连接提示下载firefox-->
<script>
    var canvas1=document.getElementById(&#39;canvas1&#39;);
    var context1=canvas1.getContext(&#39;2d&#39;);
    image=new Image();
    image.src="photo.jpg";
    context1.drawImage(image,0,0);//绘制原始图像，（0,0）表示图像的左上角位与canvas画布的位置
var imagedata1=context1.getImageData(0,0,image.width,image.height);
    var imagedata2=context1.createImageData(image.width,image.height);    
    r=40;//放大镜半径,原始默认值，可以通过最下面的进度条设置
    canvas1.onmousemove=function(e){
       var x=e.clientX-e.target.offsetLeft;
       var y=e.clientY-e.target.offsetTop;
       x0=x;y0=y;
       //console.log(&#39;x:&#39;+x+&#39;y:&#39;+y);
for (var j=0;j<image.height;j++){
         for(var i=0;i<image.width;i++){
           var k=4*(image.width*j+i);
           var k1=4*(image.width*Math.floor((j+y0)/2)+Math.floor((i+x0)/2));//对应的原始图像上的点
           if (isOn(x0,y0,i,j,r)){//放大镜边缘上的点
              imagedata2.data[k+0]=0;
              imagedata2.data[k+1]=0;
              imagedata2.data[k+2]=0;
              imagedata2.data[k+3]=255;
              }
           else if(isIn(x0,y0,i,j,r)){//放大区域的点
              if(k1>=0&&k1<=4*image.height*image.width){//放大效果的的时候，这一步其实可以省略
              imagedata2.data[k+0]=imagedata1.data[k1+0];
              imagedata2.data[k+1]=imagedata1.data[k1+1];
              imagedata2.data[k+2]=imagedata1.data[k1+2];
              imagedata2.data[k+3]=255;
             // console.log(&#39;x:&#39;+x+&#39;y:&#39;+y);
          }
          }
          else{//其他剩下不受影响的点
              imagedata2.data[k+0]=imagedata1.data[k+0];
              imagedata2.data[k+1]=imagedata1.data[k+1];
              imagedata2.data[k+2]=imagedata1.data[k+2];
              imagedata2.data[k+3]=255;
          }
       }}
       context1.putImageData(imagedata2,0,0);//canvas显示
    }
    canvas1.onmouseout=function(){context1.drawImage(image,0,0);}//鼠标移出，自动重绘
    function isIn(x0,y0,x,y,r){//放大区域
if((x0-x)*(x0-x)+(y0-y)*(y0-y)<r*r)
          return true;
        else
          return false;
    }
    function isOn(x0,y0,x,y,r){//放大镜边缘
if((x0-x)*(x0-x)+(y0-y)*(y0-y)==r*r)
          return true;
        else
          return false;
    }
    </script>
    <br/>
<canvas id="bar" height="30" width="305"></canvas>
&nbsp放大镜半径为<span id=&#39;r&#39;></span>
<script>
var canvas2=document.getElementById(&#39;bar&#39;);
var context2=canvas2.getContext(&#39;2d&#39;);
context2.beginPath();
context2.lineWidth = 1;//边框宽度                           
context2.strokeStyle = "#ff00ff";//边框颜色
context2.strokeRect(10,0,295,28);//边框坐标及大小
context2.closePath();
canvas2.onclick=function(e){
     var x1=e.clientX-e.target.offsetLeft;
     context2.clearRect(0,0,305,30);
     context2.beginPath();
     context2.lineWidth = 1;//边框宽度                           
     context2.strokeStyle = "#ff00ff";//边框颜色
     context2.strokeRect(10,0,295,28);//边框坐标及大小
     context2.fillStyle = "#00ff00";//填充canvas的背景颜色
     context2.fillRect(0, 0, x1,28);//参数分别表示 x轴,y轴,宽度,高度
     document.getElementById(&#39;r&#39;).innerHTML=Math.floor(x1/6);
     r=Math.floor(x1/6);//一个划算，使得最大半径为50px
}
</script>
</body>  
</html>

Attention:

1) Remember to set the width and height of canvas1 to be the same size as the

picture

. If they are different, set the It is troublesome to perform this calculation;The effect is as follows:

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