canvas实现图片压缩及复制
canvas实现图片压缩及复制
context.drawImage(img,originXFrom,originYFrom,imgBeforeWidth,imgBeforeHeight,toCanvasFromX,toCanvasFromY,imgAfterWidth,imgAfterHeight)参数介绍：
- img：原图像
- originXFrom：引用原图像时在原图像的横轴偏移位置
- originYFrom：引用原图像时在原图像的纵轴偏移位置
- imgBeforeWidth：原图像的width
- toCanvasFromX：从canvas的横轴偏移位置开始画图
- 这里写imgAfterWidth：压缩后图片width
2. canvas.toDataURL('image/type',quality)
参数介绍：
- type：将要生成的图像类型，默认为png，可指定为jpg
或者webp ，若指定的类型错误，则使用默认设置
- quality：图像压缩质量，范围[0,1]，数值越小，压缩比例越大
3. imageData = context.getImageData(xFrom,yFrom,xTo,yTo)
imageData的值中data为数组，将每个像素点转换为4个字节，分别表示rgba，a一般为255，a=255表示完全可见，a=0表示完全透明
4. context.putImageData(imageData,fromX,fromY)
参数介绍：
- imageData：由getImageData得到的值
- fromX：从画布的偏移位置开始画
实例代码
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Titletitle>
head>
<body>
<div id="img1">
<img data-src="123.jpg" src="" alt="left ear" id="i">
div>
<canvas id="canvasCopy">canvas>
<script type="text/javascript">
var ele = document.getElementById('i'),
url =ele.dataset.src,
afterWidth = 214,
afterHeight = 300,
quality = 0.3;
setImage(url,afterWidth,afterHeight,quality,ele);
function setImage(url,afterWidth,afterHeight,quality,ele) {
var image = new Image();
image.onload = function () {
var canvas = document.createElement('canvas'),
context = canvas.getContext('2d'),
beforeWidth = this.width,
beforeHeight = this.height,
dataurl = '';
canvas.width = afterWidth;
canvas.height = afterHeight;
context.drawImage(image,0, 0, beforeWidth, beforeHeight, 0, 0, afterWidth, afterHeight );
dataurl = canvas.toDataURL('image/webp',quality);
/*
* 以下是getImageData和putImageData的使用细节*/
var imagedata = context.getImageData(0,0,afterWidth,afterHeight);
console.log(imagedata)
var canvasCopy = document.getElementById('canvasCopy');
canvasCopy.width = afterWidth;
canvasCopy.height = afterHeight;
canvasCopy.getContext('2d').putImageData(imagedata,0,0);
ele.src = dataurl;
image.onload = null;
};
image.src = url;
}
script>
body>
html>