js canvas實現(xiàn)放大鏡查看圖片功能

更新時間：2017年06月08日 15:43:50 作者：我在世界的盡頭想你

這篇文章主要為大家詳細介紹了js canvas實現(xiàn)放大鏡查看圖片功能，具有一定的參考價值，感興趣的小伙伴們可以參考一下

本文實例為大家分享了canvas實現(xiàn)放大鏡查看圖片功能的具體代碼，供大家參考，具體內(nèi)容如下

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body style="background: black;">
<canvas id="myCanvas" style="display: block;margin: 0px auto;border: 10px solid #aaa ">
  你的瀏覽器不支持canvas
</canvas>
<canvas id="offCanvas" style="display: none"></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內(nèi)容，希望對大家的學習有所幫助，也希望大家多多支持腳本之家。

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