这篇文章主要介绍了原生js基于canvas实现一个简单的前端截图工具代码实例,文中通过示例代码介绍的非常详细，对大家的学习或者工作具有一定的参考学习价值,需要的朋友可以参考下
先看效果
代码如下
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title></title> <style type="text/css"> *{ padding: 0; margin: 0; } .clip-img-w{ position: relative; width: 100%; height: 100%; font-size: 0; } .clip-img-w img{ max-width: 100%; max-height: 100%; position: absolute; left: 0; top: 0; right: 0; bottom: 0; margin: auto; } .clip-img-w canvas{ position: absolute; left: 0; top: 0; } .clip-img-w #clipcanvas{ z-index: 2; } .clip-img-w #drawcanvas{ background: #fff; z-index: 1; } #img{ display: block; margin: 0 auto; } .box-c{ width: 400px; height: 200px; border: 1px solid #F35252; margin: 20px auto; } </style> </head> <body> <div> <div> <canvas ></canvas> <canvas ></canvas> </div> </div> <!-- 结果 --> <img src=""> </body> <script type="text/javascript"> var img = document.getElementById("img"); var url = 'http://img.muchengfeng.cn/FvC7i-GkXYoHE7kGFlNfj7xEzvIQ'; var wrap = document.getElementById("clip-img-w"); var width = wrap.offsetWidth; var height = wrap.offsetHeight; var clipcanvas = document.getElementById("clipcanvas"); var drawcanvas = document.getElementById("drawcanvas"); clipcanvas.width = width; clipcanvas.height = height; drawcanvas.width = width; drawcanvas.height = height; var clipCtx = drawcanvas.getContext("2d"); var clipImg = document.createElement("img"); clipImg.crossOrigin = "anonymous"; clipImg.src = url; var timg = clipImg.cloneNode(); wrap.appendChild(clipImg); clipImg.onload = function(){ var x = Math.floor((width - this.width)/2); var y = Math.floor((height - this.height)/2); clipCtx.drawImage(this,0,0,timg.width,timg.height,x,y,this.width,this.height); } var ctx = clipcanvas.getContext("2d"); ctx.fillStyle = 'rgba(0,0,0,0.6)'; ctx.strokeStyle="green"; var start = null; var clipArea = {};//裁剪范围 clipcanvas.onmousedown = function(e){ start = { x:e.offsetX, y:e.offsetY }; } clipcanvas.onmousemove = function(e){ if(start){ fill(start.x,start.y,e.offsetX-start.x,e.offsetY-start.y) } } document.addEventListener("mouseup",function(){ if(start){ start = null; var url = startClip(clipArea); img.src= url; } }) function fill(x,y,w,h){ ctx.clearRect(0,0,width,height); ctx.beginPath(); //遮罩层 ctx.globalCompositeOperation = "source-over"; ctx.fillRect(0,0,width,height); //画框 ctx.globalCompositeOperation = 'destination-out'; ctx.fillRect(x,y,w,h); //描边 ctx.globalCompositeOperation = "source-over"; ctx.moveTo(x,y); ctx.lineTo(x+w,y); ctx.lineTo(x+w,y+h); ctx.lineTo(x,y+h); ctx.lineTo(x,y); ctx.stroke(); ctx.closePath(); clipArea = { x, y, w, h }; } function startClip(area){ var canvas = document.createElement("canvas"); canvas.width = area.w; canvas.height = area.h; var data = clipCtx.getImageData(area.x,area.y,area.w,area.h); var context = canvas.getContext("2d"); context.putImageData(data,0,0); return canvas.toDataURL("image/png"); } </script> </html>