除了jquery，本插件还引用了UI库，包括ui.draggable.js
ImageCropper 演示需要asp.net支持。测试通过
ImageCropper 下载 https://www.jb51.net/jiaoben/25688.html
插件用法：
复制代码 代码如下:
var imageCropper = $('#imgBackground').imageCropper();

要注意的是此插件只应用在有src属性的img标签上。
通过插件输出的参数，即可以通过服务器端代码截取图片，比如：
复制代码 代码如下:
$('#imgCroppedImage').attr('src', 'CropImage.ashx?p=' + imageCropper.settings.imagePath + '&z=' + imageCropper.settings.zoomLevel + '&t=' + imageCropper.settings.top + '&l=' + imageCropper.settings.left + '&w=' + imageCropper.settings.width + '&h=' + imageCropper.settings.height + '&' + Math.random());

asp.net hander CropImage.ashx:
复制代码 代码如下:
public class CropImage : IHttpHandler
{
public void ProcessRequest(HttpContext context)
{
string imgPath = Convert.ToString(context.Request["p"]);
float zoomLevel = Convert.ToSingle(context.Request["z"]);
int top = Convert.ToInt32(context.Request["t"]);
int left = Convert.ToInt32(context.Request["l"]);
int width = Convert.ToInt32(context.Request["w"]);
int height = Convert.ToInt32(context.Request["h"]);
context.Response.ContentType = "image/jpeg";
Crop(HttpContext.Current.Server.MapPath(imgPath), zoomLevel, top, left, width, height).WriteTo(context.Response.OutputStream);
}
public MemoryStream Crop(string imgPath, float zoomLevel, int top, int left, int width, int height)
{
Image img = Image.FromFile(imgPath);
Bitmap bitmap = new Bitmap(width, height);
Graphics g = Graphics.FromImage(bitmap);
g.DrawImage(img, new Rectangle(0, 0, width, height), new Rectangle((int)(left / zoomLevel), (int)(top / zoomLevel), (int)(width / zoomLevel), (int)(height / zoomLevel)), GraphicsUnit.Pixel);
MemoryStream ms = new MemoryStream();
bitmap.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
img.Dispose();
g.Dispose();
bitmap.Dispose();
return ms;
}
public bool IsReusable
{
get
{
return false;
}
}
}

重点是插件，因为源代码注释比较全，直接贴代码在这：
复制代码 代码如下:
/**
* Copyright (c) 2010 Viewercq (http://www.cnblogs.com/viewercq/archive/2010/04/04/1704093.html)
* Dual licensed under the MIT (http://www.opensource.org/licenses/mit-license.php)
* and GPL (http://www.opensource.org/licenses/gpl-license.php) licenses.
*
* Version: 1.0
*
* Demo: https://dl.dropbox.com/u/4390741/ImageCropper.htm
*/
; (function($) {
$.fn.extend({
imageCropper: function(options) {
if (!this.is('img') || typeof this.attr('src') == 'undefined' || this.attr('src') == '') {
throw 'Please notice that this jquery plguin only could be applied to img and the src of img could not be null!';
}
var defaults = {
//原图路径
imagePath: this.attr('src'),
//缩放级别
zoomLevel: 1,
//图片相对于截取框是否居中
center: false,
//截取框与图片的相对位置
left: 0, top: 0,
//截取框的大小
width: 200, height: 200,
//工作区大小
cropWorkAreaSize: { width: 600, height: 400 },
//截取框相对于工作区的位置
cropFrameRect: { center: true, top: 0, left: 0 },
//缩放范围
zoom: { min: 0, max: 2, step: 0.01 },
//回调函数
callbacks: {
//移动图片后
dragging: false,
//缩放后
zoomed: false
}
};
if (options) {
defaults = $.extend(defaults, options);
}
return new imageCropper(this, defaults);
}
});
function imageCropper(image, settings) {
this.init(image, settings);
};
imageCropper.prototype = {
settings: false,
wrapper: $('<div class="image-cropper-wrapper"/>'),
zoomWrapper: $('<div class="zoom-wrapper"><div class="zoom-out-button"/><div class="zoom-scrollbar"><div class="zoom-scroller"/></div><div class="zoom-in-button"/></div>'),
img: false,
init: function(image, settings) {
var context = this;
this.settings = settings;
image.addClass('background-img');
//生成html
image.wrap(this.wrapper).wrap('<div class="crop-work-area"/>').wrap('<div class="crop-background"/>');
this.wrapper = $('.image-cropper-wrapper');
$('.crop-work-area', this.wrapper).append('<div class="crop-frame"><img class="foreground-img" src="/UploadFiles/2021-04-02/">this.wrapper.append(this.zoomWrapper);
$('.image-cropper-wrapper', this.wrapper).disableSelection();
this.reset();
//图片的拖动
$('.crop-background', this.wrapper).draggable({
containment: $('.drag-containment', this.wrapper),
cursor: 'move',
drag: function(event, ui) {
var self = $(this).data('draggable');
//同时移动前景图
$('.foreground-img', this.wrapper).css({
left: (parseInt(self.position.left) - context.settings.cropFrameRect.left - 1) + 'px',
top: (parseInt(self.position.top) - context.settings.cropFrameRect.top - 1) + 'px'
});
//得到截图左上点坐标
context.settings.left = context.settings.cropFrameRect.left - parseInt($(this).css('left'));
context.settings.top = context.settings.cropFrameRect.top - parseInt($(this).css('top'));
//移动图片的callback
context.fireCallback(context.settings.callbacks.dragging);
}
});
$('.foreground-img', this.wrapper).draggable({
containment: $('.drag-containment', this.wrapper),
cursor: 'move',
drag: function(event, ui) {
var self = $(this).data('draggable');
//同时移动背景
$('.crop-background', this.wrapper).css({
left: (parseInt(self.position.left) + context.settings.cropFrameRect.left + 1) + 'px',
top: (parseInt(self.position.top) + context.settings.cropFrameRect.top + 1) + 'px'
});
//得到截图左上点坐标
context.settings.left = context.settings.cropFrameRect.left - parseInt($('.crop-background', this.wrapper).css('left'));
context.settings.top = context.settings.cropFrameRect.top - parseInt($('.crop-background', this.wrapper).css('top'));
//移动图片的callback
context.fireCallback(context.settings.callbacks.dragging);
}
});
//点击缩放
$('.zoom-out-button,.zoom-in-button', this.wrapper).click(function() {
var step = $(this).hasClass('zoom-in-button') ? context.settings.zoom.step : -context.settings.zoom.step;
var tempZoomLevel = context.formatNumber(context.settings.zoomLevel + step, 3);
//如果缩放级别超出范围 或者 缩放导致图片右下角没在截取框内 则取消缩放
if (context.settings.zoomLevel >= context.settings.zoom.min
&& context.settings.zoomLevel <= context.settings.zoom.max
&& parseInt($('.crop-background', this.wrapper).css('left')) + tempZoomLevel * context.img.width > context.settings.cropFrameRect.left + context.settings.width
&& parseInt($('.crop-background', this.wrapper).css('top')) + tempZoomLevel * context.img.height > context.settings.cropFrameRect.top + context.settings.height
) {
context.settings.zoomLevel = tempZoomLevel;
context.zoom(context.img.width * context.settings.zoomLevel, context.img.height * context.settings.zoomLevel);
$('.zoom-scroller', this.wrapper).css('left', context.settings.zoomLevel * 200 / (context.settings.zoom.max - context.settings.zoom.min) + 'px');
}
context.fireCallback(context.settings.callbacks.zoomed);
});
//滚动条缩放
var cancelZoomScroll = false;
$('.zoom-scroller', this.wrapper).draggable({
containment: $('.zoom-scrollbar', this.wrapper),
axis: 'x',
drag: function(event, ui) {
var tempZoomLevel = (context.settings.zoom.max - context.settings.zoom.min) * parseInt($(this).css('left')) / 200;
//如果缩放级别超出范围 或者 缩放导致图片右下角没在截取框内 则取消缩放
if (parseInt($('.crop-background', this.wrapper).css('left')) + tempZoomLevel * context.img.width > context.settings.cropFrameRect.left + context.settings.width
&& parseInt($('.crop-background', this.wrapper).css('top')) + tempZoomLevel * context.img.height > context.settings.cropFrameRect.top + context.settings.height
) {
context.settings.zoomLevel = tempZoomLevel;
context.zoom(context.img.width * context.settings.zoomLevel, context.img.height * context.settings.zoomLevel);
cancelZoomScroll = false;
context.fireCallback(context.settings.callbacks.zoomed);
}
else {
cancelZoomScroll = true;
}
},
stop: function(event, ui) {
//如果缩放级别无效 则重置滚动条的值
if (cancelZoomScroll) {
$('.zoom-scroller', this.wrapper).css('left', context.settings.zoomLevel * 200 / (context.settings.zoom.max - context.settings.zoom.min) + 'px');
}
}
});
},
reset: function() {
this.img = new Image();
this.img.src = this.settings.imagePath;
//截取框大于工作区，则放大工作区
var tempSize = {
width: Math.max(this.settings.cropWorkAreaSize.width, this.settings.width),
height: Math.max(this.settings.cropWorkAreaSize.height, this.settings.height)
};
//如果截取框在工作区中居中，则重新设置截取框的位置
if (this.settings.cropFrameRect.center) {
this.settings.cropFrameRect.left = (tempSize.width - this.settings.width) / 2;
this.settings.cropFrameRect.top = (tempSize.height - this.settings.height) / 2;
}
//如果截取框在图片中居中，则重新设置图片与截取框的相对位置
if (this.settings.center) {
this.settings.left = (this.img.width * this.settings.zoomLevel - this.settings.width) / 2;
this.settings.top = (this.img.height * this.settings.zoomLevel - this.settings.height) / 2;
}
this.wrapper.width(tempSize.width + 2).height(tempSize.height + 25);
$('.foreground-img,.background-img', this.wrapper).attr('src', this.settings.imagePath);
$('.crop-work-area', this.wrapper).width(tempSize.width).height(tempSize.height);
$('.crop-frame', this.wrapper).css({
left: this.settings.cropFrameRect.left + 'px',
top: this.settings.cropFrameRect.top + 'px',
width: this.settings.width + 'px',
height: this.settings.height + 'px'
});
$('.foreground-img', this.wrapper).css({
left: (-this.settings.cropFrameRect.left - 1) + 'px',
top: (-this.settings.cropFrameRect.top - 1) + 'px'
});
$('.zoom-scroller', this.wrapper).css('left', this.settings.zoomLevel * 200 / (this.settings.zoom.max - this.settings.zoom.min) + 'px');
$('.crop-background', this.wrapper).css({
opacity: 0.3,
left: this.settings.cropFrameRect.left - this.settings.left + 'px',
top: this.settings.cropFrameRect.top - this.settings.top + 'px'
});
$('.foreground-img', this.wrapper).css({
left: -this.settings.left + 'px',
top: -this.settings.top + 'px'
});
this.settings.left = this.settings.cropFrameRect.left - parseInt($('.crop-background', this.wrapper).css('left'));
this.settings.top = this.settings.cropFrameRect.top - parseInt($('.crop-background', this.wrapper).css('top'));
this.zoom(this.img.width * this.settings.zoomLevel, this.img.height * this.settings.zoomLevel);
},
zoom: function(width, height) {
$('.crop-background, .background-img, .foreground-img', this.wrapper).width(width).height(height);
//调整拖动限制框
$('.drag-containment', this.wrapper).css({
left: this.settings.cropFrameRect.left + this.settings.width - this.settings.zoomLevel * this.img.width + 1 + 'px',
top: this.settings.cropFrameRect.top + this.settings.height - this.settings.zoomLevel * this.img.height + 1 + 'px',
width: 2 * this.settings.zoomLevel * this.img.width - this.settings.width + 'px',
height: 2 * this.settings.zoomLevel * this.img.height - this.settings.height + 'px'
});
},
formatNumber: function(number, bit) {
return Math.round(number * Math.pow(10, bit)) / Math.pow(10, bit);
},
fireCallback: function(fn) {
if ($.isFunction(fn)) {
fn.call(this);
};
}
};
})(jQuery);