本文實例講述了JavaScript+HTML5 canvas實現放大鏡效果。分享給大家供大家參考，具體如下：
效果：
<!DOCTYPE html><html><head lang="en"> <meta charset="UTF-8"> <title>m.survivalescaperooms.com canvas放大鏡</title> <style> #copycanvas { border: 1px solid #000; display: none; } #square { width: 90px; height: 90px; background-color: #cc3; border: 1px solid #f00; opacity: 0.5; position: absolute; z-index: 999; display: none; cursor: crosshair; } </style></head><body><canvas id="canvas" width="450" height="676"></canvas><canvas id="copycanvas" width="300" height="300"></canvas><div id="square"></div><script> var canvas = document.getElementById('canvas'), //獲取canvas對象 context = canvas.getContext('2d'), //獲取上下文 copycanvas = document.getElementById('copycanvas'), //獲取copycanvas copycontext = copycanvas.getContext('2d'), square = document.getElementById('square'), //獲取透明框 squaredata = {}, //用來保存選擇框數據 box = canvas.getBoundingClientRect(); //getBoundingClientRect方法可以獲取元素上、下、左、右分別相對瀏覽器的坐標位置 //創建圖像對象，并加載 image = new Image(); image.src = "3.jpg"; image.onload = function(){ context.drawImage(image,0,0,canvas.width,canvas.height); }; canvas.onmouseover = function(e){ var x = e.clientX, //獲取鼠標實時坐標 y = e.clientY; createSquare(x,y); //保存透明選擇框屬性 }; window.onmousemove = function(e){ var x = e.clientX, y = e.clientY; //判斷鼠標是否移出canvas if(x >= canvas.offsetLeft && x <= canvas.offsetLeft + canvas.width && y >= canvas.offsetTop && y <= canvas.offsetTop + canvas.height){ createSquare(x,y); }else{ hideSquare(); hideCanvas(); } } function showSquare(){ square.style.display = 'block'; } function hideSquare(){ square.style.display = 'none'; } function showCanvas(){ copycanvas.style.display = "inline"; } function hideCanvas(){ copycanvas.style.display = "none"; } function createSquare(x,y){ //控制選擇框不移動出canvas x = x - 45 < canvas.offsetLeft ? canvas.offsetLeft:x - 45; y = y - 45 < canvas.offsetTop ? canvas.offsetTop:y - 45; x = x + 90 < box.right ? x:box.right - 90; y = y + 90 < box.bottom ? y:box.bottom - 90; squaredata.left = x; squaredata.top = y; moveSquare(x,y); } function moveSquare(x,y){ square.style.left = x + "px"; square.style.top = y + "px"; showCanvas(); showSquare(); copy(); } function copy(){ copycontext.drawImage( canvas, squaredata.left - box.left, squaredata.top - box.top, 90, 90, 0, 0, copycanvas.width, copycanvas.height ); }</script></body></html>感興趣的朋友可使用在線HTML/CSS/JavaScript代碼運行工具：http://tools.VeVB.COm/code/HtmlJsRun測試一下運行效果。
更多關于JavaScript相關內容感興趣的讀者可查看本站專題：《JavaScript圖片操作技巧大全》、《JavaScript運動效果與技巧匯總》、《JavaScript+HTML5特效與技巧匯總》、《JavaScript圖形繪制技巧總結》、《JavaScript數據結構與算法技巧總結》及《JavaScript數學運算用法總結》
希望本文所述對大家JavaScript程序設計有所幫助。
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