本文是一个简单的jquery图片预览+裁剪的例子，原理是在前端获取要裁剪的信息，如宽高比、裁剪坐标，上传图片之后在后端php进行切割
jquery代码（必须在最后面引入）
function showCutImg(showImg){ var showImg = $(showImg); var changeInput = showImg.parents('.showImgDiv').siblings('.CutImage'); var size = changeInput.siblings('.imgCoord').attr('ratio').split('*'); var needWidth = size[0]; var needHeight = size[1]; var ratio = parseInt(needWidth)/parseInt(needHeight); ratio = parseFloat(ratio.toFixed(2)); var thisFullDiv = showImg.parent(); var coordArr = changeInput.siblings('.imgCoord').val().split(','); thisCutImgWidth = showImg.width(); thisCutImgHeight = showImg.height() thisFullDiv.css('width',thisCutImgWidth); thisFullDiv.css('height',thisCutImgHeight); if((thisCutImgWidth/thisCutImgHeight)>=ratio){ var thisCutDivHeight = thisCutImgHeight; var thisCutDivWidth = thisCutDivHeight*ratio; }else{ var thisCutDivWidth = thisCutImgWidth; var thisCutDivHeight = thisCutDivWidth/ratio; } var hideWidth = (thisFullDiv.width()-thisCutDivWidth)/2; showImg.siblings('.hideImgLeft').width(hideWidth); showImg.siblings('.hideImgRight').width(hideWidth); var hideHeight = (thisFullDiv.height()-thisCutDivHeight)/2; showImg.siblings('.hideImgTop').width(thisCutDivWidth); showImg.siblings('.hideImgBottom').width(thisCutDivWidth); showImg.siblings('.hideImgTop').height(hideHeight); showImg.siblings('.hideImgBottom').height(hideHeight); if(hideWidth>0){ var cutRatioX = thisCutImgWidth/hideWidth; }else{ var cutRatioX = 0 } if(hideHeight>0){ var cutRatioY = thisCutImgHeight/hideHeight; }else{ var cutRatioY = 0; } var coord = needWidth+'#'+needHeight+'#'+(cutRatioX)+'#'+(cutRatioY); if(coordArr!=''){ coordArr.push(coord); }else{ coordArr = [coord]; } changeInput.siblings('.imgCoord').val(coordArr); $('.fullDiv').on('mousedown',function(e){ var me = $(this); var changeInput = me.parent().siblings('.CutImage'); var index = me.attr('index'); var oldx = e.pageX; var oldy = e.pageY; var imgleft = me.children('.cutImg').position().left; var imgtop = me.children('.cutImg').position().top; var maxw = me.children('.hideImgLeft').width(); var maxh = me.children('.hideImgTop').height(); var goordArr = changeInput.siblings('.imgCoord').val().split(','); var cutDivSize = goordArr[index].split('#'); $(document).mousemove(function(e){ var newx = e.pageX; var newy = e.pageY; var movex = newx - oldx; var movey = newy - oldy; var x = movex + imgleft; var y = movey + imgtop; if(Math.abs(x)>maxw){ if(x>0) x = maxw; if(x<0) x = -maxw; } if(Math.abs(y)>maxh){ if(y>0) y = maxh; if(y<0) y = -maxh; } me.children('.cutImg').css('left',x+'px'); me.children('.cutImg').css('top',y+'px'); if(parseInt(maxw - x)>0){ var cutRatioX = me.children('.cutImg').width()/parseInt(maxw - x); }else{ var cutRatioX = 0; } if(parseInt(maxh - y)>0){ var cutRatioY = me.children('.cutImg').height()/parseInt(maxh - y) }else{ var cutRatioY = 0; } var cutImgPo = (cutRatioX) +'#'+ (cutRatioY); var coordVal = cutDivSize[0]+'#'+cutDivSize[1]+'#'+cutImgPo; goordArr[index] = coordVal; changeInput.siblings('.imgCoord').val(goordArr); }); }); $(document).on('mouseup',function(e){ $(document).unbind('mousemove'); }); } $(".CutImage").change(function(){ $(this).siblings('.imgCoord').val(''); if($(this).prop('multiple')!=true){ //判断是否多文件上传 var objUrl = getObjectURL1(this.files[0]) ; var showImgWidth = $(this).siblings('.showImgDiv').attr('showImgWidth'); if(!showImgWidth) { showImgWidth = '150'; } if (objUrl) { html = ''; html += '<div index="0">'; html += '<div></div>'; html += '<div></div>'; html += '<div></div><div></div>'; html += '<div></div>'; html += '<img src="'https://www.jb51.net/+objUrl+'" alt="图片加载失败" />'; html += '</div>'; $(this).siblings('.showImgDiv').html(html); } }else{ var objUrl = getObjectURL2($(this).get(0).files); if (objUrl) { var showImgWidth = $(this).siblings('.showImgDiv').attr('showImgWidth'); if(!showImgWidth) { showImgWidth = '150'; } var html = ''; for(var i=0;i<objUrl.length;i++) { html += '<div index="'+i+'">'; html += '<div></div>'; html += '<div></div>'; html += '<div></div><div></div>'; html += '<div></div>'; html += '<img src="'https://www.jb51.net/+objUrl[i]+'" alt="图片加载失败" />'; html += '</div>'; //修改img标签的width样式可改变预览图大小 } $(this).siblings('.showImgDiv').html(html); } //$('.fullDiv').css('float','left'); } }) ; //建立一個可存取到該file的url function getObjectURL1(file) { var url = null ; if (window.createObjectURL!=undefined) { // basic url = window.createObjectURL(file) ; } else if (window.URL!=undefined) { // mozilla(firefox) url = window.URL.createObjectURL(file) ; } else if (window.webkitURL!=undefined) { // webkit or chrome url = window.webkitURL.createObjectURL(file) ; } return url ; } //建立一個可存取到該file的url function getObjectURL2(file) { var url = new Array(); if (window.createObjectURL!=undefined) { // basic for(var i=0;i<file.length;i++) { url[i] = window.createObjectURL(file[i]) ; } } else if (window.URL!=undefined) { // mozilla(firefox) for(var i=0;i<file.length;i++) { url[i] = window.URL.createObjectURL(file[i]) ; } } else if (window.webkitURL!=undefined) { // webkit or chrome for(var i=0;i<file.length;i++) { url[i] = window.webkitURL.createObjectURL(file[i]) ; } } return url ; }
html代码（这些代码要放在同一级）