给大家整理一篇相关的编程文章，网友蒯新月根据主题投稿了本篇教程内容，涉及到js、canvas、放大镜、js canvas实现放大镜查看图片功能相关内容，已被294网友关注，涉猎到的知识点内容可以在下方电子书获得。
js canvas实现放大镜查看图片功能
本文实例为大家分享了canvas实现放大镜查看图片功能的具体代码，供大家参考，具体内容如下
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body >
<canvas id="myCanvas" >
你的浏览器不支持canvas
</canvas>
<canvas id="offCanvas" ></canvas>
<script>
var myCanvas = document.getElementById("myCanvas");
var context = myCanvas.getContext("2d");
var offCanvas = document.getElementById("offCanvas");
var offContext = offCanvas.getContext("2d");
var isMouseDown = false;
var scale;
var image = new Image();
window.onload = function () {
myCanvas.width = 300;
myCanvas.height = 200;
image.src = "1.jpg";
image.onload = function () {
offCanvas.width = image.width;
offCanvas.height = image.height;
scale = offCanvas.width / myCanvas.width ;
context.drawImage(image,0,0,myCanvas.width,myCanvas.height);
offContext.drawImage(image,0,0);
}
};
function windowToCanvas(x,y) {
var bbox = myCanvas.getBoundingClientRect();
return { x : x - bbox.left , y : y - bbox.top};
}
myCanvas.onmousedown = function (e) {
e.preventDefault();
var point = windowToCanvas(e.clientX , e.clientY);
console.log(point);
isMouseDown = true;
drawCanvasWithMagnifier( true , point );
};
myCanvas.onmousemove = function (e) {
e.preventDefault();
if (isMouseDown ){
var point = windowToCanvas(e.clientX , e.clientY);
drawCanvasWithMagnifier( true , point );
}
};
myCanvas.onmouseup = function (e) {
e.preventDefault();
isMouseDown = false;
drawCanvasWithMagnifier( false );
};
myCanvas.onmouseout = function (e) {
e.preventDefault();
isMouseDown = false;
drawCanvasWithMagnifier( false );
};
function drawCanvasWithMagnifier( isShowMagnifier , point) {
context.clearRect(0,0,myCanvas.width,myCanvas.height);
context.drawImage(image,0,0,myCanvas.width,myCanvas.height);
if(isShowMagnifier == true ){
drawMagnifier( point );
}
}
function drawMagnifier( point ) {
var imageLG_cx = point.x * scale ;
var imageLG_cy = point.y * scale ;
var mr = 20 ;
var sx = imageLG_cx - mr ;
var sy = imageLG_cy - mr ;
var dx = point.x - mr ;
var dy = point.y - mr ;
context.save();
context.lineWidth = 5.0;
context.strokeStyle = "#069";
context.beginPath();
context.arc(point.x,point.y,mr,0,Math.PI*2);
context.stroke();
context.clip();
context.drawImage(offCanvas,sx,sy,2*mr,2*mr,dx,dy,2*mr,2*mr);
context.restore();
}
</script>
</body>
</html>
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持码农之家。
