html5 worker 实例（二）图片变换_html worker new image()-优快云博客

本文链接：https://blog.youkuaiyun.com/gointoit/article/details/9155195

这篇博客通过HTML5 Worker展示了图片灰度变换的效果。当鼠标悬停在图片上时，Worker在后台处理图片像素，将图片转换为灰度，不影响页面性能。实现过程中，需要引入jQuery库，并在img标签中指定要变换的图片。

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worker的js代码

img.js

onmessage = function(e) {
	postMessage(filter(e.data))
};
function filter(imgd) {
	var pix = imgd.pixels.data;
	var xcord = imgd.x / 1000;
	var ycord = imgd.y / 1000;
	for ( var i = 0, n = pix.length; i < n; i += 4) {
		var grayscale = pix[i] * xcord + pix[i + 1] * .59 + pix[i + 2] * .11;
		pix[i] = grayscale; // red
		pix[i + 1] = grayscale; // green
		pix[i + 2] = grayscale; // blue
	}
	imgd['pixels'].data = pix;
	return imgd;
}

html代码

<!DOCTYPE html>
<html>
<head>
<title>test2.html</title>

<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="this is my page">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">

<!--<link rel="stylesheet" type="text/css" href="./styles.css">-->
<script type="text/javascript" src="../js/jquery-1.8.0.min.js"></script>
</head>

<body>
	<canvas id="myCanvas" width="640" height="480"></canvas>
	<img src="../image/psu[4].jpg" class="onHover"> //注意，自己在这里插入一张图片，否则没用效果
	<script type="text/javascript">
     function process(img,x,y){
    	 var canvas = document.getElementById("myCanvas");
    	 var context = canvas.getContext('2d');
    	     context.drawImage(img, 0, 0);
    	 var pixels = context.getImageData(0,0,img.width,img.height);
    	 var worker = new Worker("img.js");
    	 var obj = {
    			 pixels: pixels,
    			 x:x,
    			 y:y
    			 }
    	     worker.postMessage(obj);
    	     worker.onmessage = function(e) {
    		 if (typeof e.data === "string") {
    		    console.log("Worker: " + e.data);
    		    return; 
    		 }
    		 var new_pixels = e.data.pixels; // Pixels from worker
    		 context.putImageData(new_pixels, 0, 0);
    		 img.src = canvas.toDataURL(); // And then to the img
    		 }
          }
   </script>
	<script type="text/javascript">
   $(function(){
	   $(".onHover").on("mouseover", function(){
		   var x =this.width;
		   var y = this.height;
		   console.log("X: " + x + " Y: " + y);
		   process(this, x, y);
		   });
   })
  
  </script>
</body>
</html>

是执行上面的例子的时候，要自己引入jquery包，并且在html页面上的img标签上放入自己要变换的图片。然后部署到服务器，打开页面，当鼠标移动到图片的上面的时候就会发生变换，在这里执行变换功能的函数有worker负责，随意不影响页面本身的效率，类似于java语言中的多线程。