<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>canvas</title>
<script type="text/javascript" src="../js/jQuery.js"></script>
<style type="text/css">
*{
margin: 0;
padding: 0;
outline: none;
border: none;
}
canvas{
width: 4rem;
float: left;
border: 1px solid black;
}
canvas:nth-child(2){
float: right;
}
button{
float: left;
padding: .1rem .2rem;
font-size: .7rem;
}
</style>
</head>
<body>
<canvas id="canvasA" width="500" height="400"></canvas>
<canvas id="canvasB" width="500" height="400"></canvas>
<button id="filter">复制</button>
</body>
</html>
<script type="text/javascript">
/**
* rem 布局初始化
*/
$('html').css('font-size', $(window).width()/10);
/**
* 获取 canvas 画布
* 获取 canvas 绘图上下文环境
*/
var canvasA = $('#canvasA')[0];
var cxtA = canvasA.getContext('2d');
var canvasB = $('#canvasB')[0];
var cxtB = canvasB.getContext('2d');
/**
* 获取canvas画布的内容 getImageData
* 内容放回到canvas画布 putImageData
* 获取ImgData的每一个像素 ImgData.data
* getImageData(起始点的横坐标, 起始点的纵坐标, 获取的宽度, 获取的高度)
* putImageData(绘制点的横坐标, 绘制点点纵坐标, imgData的起始点横坐标, imgData的起始点纵坐标, 宽度, 高度)
*/
var img = new Image();
img.src = "../img/background_2.jpg";
img.onload = function(){
cxtA.drawImage(img, 0, 0, canvasA.width, canvasA.height);
}
$('#filter').on('click', function(){
var imgDataA = cxtA.getImageData(0, 0, canvasA.width, canvasA.height);
var pxData = imgDataA.data; //获取每一个像素
for(var i = 0; i < canvasB.width * canvasB.height; i++){
//灰度滤镜
var r = pxData[4*i+0];
var g = pxData[4*i+1];
var b = pxData[4*i+2];
//计算灰度的公式
var grey = 0.3*r + 0.59*g + 0.11*b;
pxData[4*i+0] = grey;
pxData[4*i+1] = grey;
pxData[4*i+2] = grey;
}
cxtB.putImageData(imgDataA, 0, 0, 0, 0, canvasB.width, canvasB.height);
});
</script>
