小编给大家分享一下js+canvas实现放大镜查看图片功能的示例，相信大部分人都还不怎么了解，因此分享这篇文章给大家参考一下，希望大家阅读完这篇文章后大有收获，下面让我们一起去了解一下吧！
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>JavaScript可以做什么
1.可以使网页具有交互性，例如响应用户点击，给用户提供更好的体验。
2.可以处理表单，检验用户的输入，并提供及时反馈节省用户时间。
3.可以根据用户的操作，动态的创建页面。
4使用JavaScript可以通过设置cookie存储在浏览器上的一些临时信息。
以上是“js+canvas实现放大镜查看图片功能的示例”这篇文章的所有内容，感谢各位的阅读！相信大家都有了一定的了解，希望分享的内容对大家有所帮助，如果还想学习更多知识，欢迎关注天达云行业资讯频道！