web功能实例 - Canvas裁剪工具

发布时间:2023年12月25日

嗯,手撸官方文档2天,发现没啥用,尤其是动画,那种计算出来的,根本想不到。因此学着学了抱着要做个东西的想法,去网上找相关案例,最终做出了这个裁剪工具。

PS :先说一下思路:

  1. 核心实现有3个canvas图层, 其中一个负责图片的预览。
  2. 另外2个叠加到一起,底层canvas负责图片的渲染; 上层的canvas负责蒙版的绘制,和选择框(挖空)区域的绘制。
  3. 我们将,移动选择框,记录的坐标和宽高,一个是同步到蒙版canvas里面,实现挖空。
  4. 第二个同步到图片渲染canvas,通过getImageData()方法,拿取选择框挖空的区域,的像素数据,渲染到图片预览canvas里面,然后通过canvas的toBlob()方法将预览canvas,导出成blobUrl,实现图片下载。

针对部分核心功能进行思路讲解。

1.上传图片

FileReader.readAsDataURL() - Web API 接口参考 | MDN (mozilla.org)

在 web 应用程序中使用文件 - Web API 接口参考 | MDN (mozilla.org)

下面,我们点击upBut,从而触发upInpchange事件,从而触发文件上传。我们对文件上传的类型进行是不是图片判断。然后,将图片File ,通过FileReader对象的readAsDataURL(File)方法,将图片File转换为dataUrl,并封装成Img对象。进而绘制到图片渲染canvas里面。

除此以外涉及到的函数,下文都会讲到。

	<input type="file" id="up-inp" name="文件上传" style="display: none" />
    <button type="button" id="up-but">上传</button>




    let upBut = document.getElementById('up-but')
    let upInp = document.getElementById('up-inp')
	upBut.addEventListener('click', (e) => { // 给按钮绑定事件,点击 input type='file',从而弹出文件上传框
			upInp.click()
		})

		// 上传图片
		const updateFile =  (e) =>{
			let file = e.target.files[0]
			if (!file.type.startsWith('image')) {
				alert('只允许上传图片')
				return
			}
			const reader = new FileReader()
			reader.onload = (e) => {  // 利用fileReader将file文件转换成dataUrl
				let img1 = new Image() // 转换成img对象,进而绘画到canvas里面
				img1.src = e.target.result
				img = img1

				img1.onload = (e) => { 
					// 读取完毕之后
					selectCropObj = computeImage({
						imgWidth: img.width,
						imgHeight: img.height,
						width: cropCardbg.width,
						height: cropCardbg.height,
					})
					initImgObj = JSON.parse(JSON.stringify(selectCropObj))

					drawImage(initImgObj)
					drawModal()
					drawClip()
					drawClipDiv()
					imgPreview()
					cropModal.style.display = 'none'
					clip.style.display = 'block'
				}
			}
			reader.readAsDataURL(file)
		}

		upInp.addEventListener('change', updateFile)

2. 蒙版绘制

蒙版说白了,就是占据canvas画布全部半透明矩形

	// 画模版
		const drawModal =  () =>{
			ctxCardbg.clearRect(0, 0, cropCardbg.width, cropCardbg.height)
			ctxCardbg.fillStyle = 'rgba(0,0,0,0.5)'
			ctxCardbg.fillRect(0, 0, cropCardbg.width, cropCardbg.height)
		}

3.挖空

挖空:蒙版随选择框的移动要扣除的透明区域。 我们先绘制蒙版,然后用clearRect()方法清除指定区域( 随着选择框移动,对应的在蒙版canvas里面的坐标和宽高围绕的区域,清除这个区域),达到挖空的效果

        // 挖空
		const drawClip = () => {
			ctxCardbg.clearRect(selectCropObj.x, selectCropObj.y, selectCropObj.w, selectCropObj.h)
		}

?4.选择框的绘制

我们先封装一个函数,用来注册拖拽选择框(中心,和8个点)的鼠标按下、移动、抬起事件

?

// 注册选择框拖拽事件
		const registerEvents = () => {
			// 注册那8个拖拽点事件
			const register = (_class) => {
				let node = document.querySelector(`.${_class}`)
				node.addEventListener('mousedown', (e) => {
					down = true
				})
				node.addEventListener('mousemove', carMouseMove)

				node.addEventListener('mouseup', function (e) {
					down = false
				})
			}

			register('top-center')
			register('bottom-center')
			register('left-center')
			register('right-center')
			register('bottom-right')
			register('bottom-left')
			register('top-right')
			register('top-left')

			// 注册拖拽中央移动的事件
			let clip = document.getElementById('crop-clip')
			clip.addEventListener('mousedown', (e) => {
				down = true
			})

			clip.addEventListener('mousemove', carMouseMove)

			clip.addEventListener('mouseup', (e) => {
				down = false
			})
		}

这是拖拽选择框的html 结构。我们的选择框采用html绘制,由于它和另外2个叠加的canvas,由于父元素相对定位,子绝对定位叠在一起,因此选择框的left和top值,就相当于canvas里面的x、y坐标,我们同样将选择框宽高映射到,canvas的挖空区域,从而在拖拽的时候实现实时挖空的效果。

?

	<div id="crop-clip" style="display: none">
				<div class="dot top-left"></div>
				<div class="dot top-right"></div>
				<div class="dot top-center"></div>
				<div class="dot bottom-left"></div>
				<div class="dot bottom-center"></div>
				<div class="dot bottom-right"></div>
				<div class="dot left-center"></div>
				<div class="dot right-center"></div>
			</div>

下面通过selectCropObj对象,记录选择框在移动期间的x,y坐标,以及选择框变化的宽高

	// 在canvas的裁剪框尺寸和坐标
		let selectCropObj = {
			x: 0,
			y: 0,
			w: 0,
			h: 0,
		}

?这是我们处理选择框移动的函数。根据拖拽的元素(选择框中央、其余8个点)的携带的class不同,从而调用不同的移动处理方法。

	// 通过拖拽事件,调用的方法(将选择框中央拖拽 ,和点拖拽通过一个函数处理)
		const carMouseMove = (e) => {
			// 两个都是false,证明我们一个没按下
			if (img === null) {
				return
			}

			if (!down) {
				return
			}

			let ele = e.target
			let { movementX, movementY } = e

			const isExistsCls = (_cls) => {
				for (let i = 0; i < ele.classList.length; i++) {
					const val = ele.classList[i]
					if (val === _cls) {
						return true
					}
				}
				return false
			}

			// 中央拖拽
			if (ele.id == 'crop-clip') {
				selectCropObj.x += movementX
				selectCropObj.y += movementY
				// 点拖拽
			} else if (isExistsCls('top-left')) {
				// 坐标和宽高的都要变
				selectCropObj.x += movementX
				selectCropObj.y += movementY
				selectCropObj.w += -movementX
				selectCropObj.h += -movementY
			} else if (isExistsCls('top-right')) {
				selectCropObj.y += movementY
				selectCropObj.w += movementX
				selectCropObj.h += -movementY
			} else if (isExistsCls('top-center')) {
				selectCropObj.y += movementY
				selectCropObj.h += -movementY
			} else if (isExistsCls('bottom-left')) {
				selectCropObj.x += movementX
				selectCropObj.y += movementY
				selectCropObj.w += -movementX
				selectCropObj.h += movementY
			} else if (isExistsCls('bottom-right')) {
				selectCropObj.w += movementX
				selectCropObj.h += movementY
			} else if (isExistsCls('bottom-center')) {
				selectCropObj.h += movementY
			} else if (isExistsCls('left-center')) {
				selectCropObj.x += movementX
				selectCropObj.w += -movementX
			} else if (isExistsCls('right-center')) {
				selectCropObj.w += movementX
			}

			drawClipDiv()
			drawModal()
			drawClip()
			imgPreview()
		}

?对应选择框的具体绘制方法。

		const drawClipDiv = () => {
			let cropClip = document.getElementById('crop-clip')
			cropClip.style.width = `${selectCropObj.w}px`
			cropClip.style.height = `${selectCropObj.h}px`
			cropClip.style.left = `${selectCropObj.x}px`
			cropClip.style.top = `${selectCropObj.y}px`
		}

5.画图像

就是清除之前渲染到图片canvas里面的图像,并将新的图片绘制到上面。

	// 画图像
		const drawImage = ({ x, y, w, h }) => {
			ctxImg.clearRect(0, 0, cropImg.width, cropImg.height)
			ctxImg.drawImage(img, x, y, w, h)
		}

6.图片旋转

CanvasRenderingContext2D.rotate() - Web API 接口参考 | MDN (mozilla.org)

关于图片旋转这里,就是现将原点移动canvas画布中央(图像中央),然后定义旋转角度,然后又将原点移动回去,然后画的图像就是围绕中心旋转的。

主要是围绕图像的中心原点旋转。

大家可以自行去网上找关于rotate让图像围绕中心原点旋转的问题。因为作者也没能明白。

// 主要是这段代码:

????????????ctxImg.translate(cropImg.width / 2, cropImg.height / 2)
?? ??? ??? ?ctxImg.rotate(angle)
?? ??? ??? ?ctxImg.translate(-cropImg.width / 2, -cropImg.height / 2)

	// 向右、左转(每次向左30度、向右30度)图片
		const imgRotate = (e, t = 1) => {
			if (img == null) {
				alert('请先上传图片')
				return
			}
			if (t == 1) {
				// 向右转,逆时针
				angle += -30 * (Math.PI / 180)
			} else {
				// 向左转,顺时针
				angle += 30 * (Math.PI / 180)
			}
			ctxImg.clearRect(0, 0, cropImg.width, cropImg.height)
			ctxImg.translate(cropImg.width / 2, cropImg.height / 2)
			ctxImg.rotate(angle)
			ctxImg.translate(-cropImg.width / 2, -cropImg.height / 2)
			drawImage(initImgObj)
			imgPreview()
		}

7.图片扩大和缩小

通过initImgObj对象,记录图像渲染到图片渲染canvas尺寸和坐标

// 图像渲染到到canvas的坐标尺寸和坐标
		let initImgObj = {
			// 主要是为了缩放/扩大图片用
			x: 0,
			y: 0,
			w: 0,
			h: 0,
		}

?通过computeImage()函数,计算出图像要在canvas画布中央实际渲染的坐标和尺寸


		// 计算图像在canvas实际渲染的图片坐标和宽高。(居于canvas中央,尺寸小于画布尺寸)
		const computeImage = function ({ imgWidth, imgHeight, width, height, base = 1 }) {
			if (imgWidth / base < width && imgHeight / base < height) {
				return {
					x: (width - imgWidth) / 2,
					y: (height - imgHeight) / 2,
					w: imgWidth / base,
					h: imgHeight / base,
				}
			}
			return computeImage({
				imgWidth,
				imgHeight,
				width,
				height,
				base: base + 0.1,
			})
		}

?通过计算?initImgObj对象的放大、缩小后的宽高,然后通过computeImage()方法计算出canvas实际渲染的图像坐标和尺寸,并渲染。


		// 缩小/扩大图片
		const imgScale = (e, t) => {
			if (img == null) {
				alert('请先上传图片')
				return
			}
			let { w, h } = initImgObj

			if (t == 1) {
				// 缩小
				w = w / 2
				h = h / 2
			} else {
				// 扩大
				w = w * 2
				h = h * 2
			}

			// 重新求出,缩小、放大之后的图片宽高和坐标。
			initImgObj = computeImage({
				imgWidth: w,
				imgHeight: h,
				width: cropImg.width,
				height: cropImg.height,
			})

			drawImage(initImgObj)
			imgPreview()
		}

8.图片预览

ImageData - Web API 接口参考 | MDN (mozilla.org)

通过选择框拖拽,记录的?selectCropObj对象的坐标和宽高信息

通过getImageData()方法获取图片渲染canvas里面的ImageData对象,并通过putImageData()方法将这个对象渲染到图片预览canvas里面。

// 图片预览
		const imgPreview = () => {
			ctxPreview.clearRect(0, 0, cropPreview.width, cropPreview.height)
			let { x, y, w, h } = selectCropObj
			let imgData = ctxImg.getImageData(x, y, w, h)
			ctxPreview.putImageData(imgData, x, y)
		}

9.保存预览图片

HTMLCanvasElement.toBlob() - Web API 接口参考 | MDN (mozilla.org)

HTMLCanvasElement.toDataURL() - Web API 接口参考 | MDN (mozilla.org)

我们通过,canvas的toBlob()方法将canvas画布转换为blobUrl,然后就是创建一个a?元素,并将这个url封装成a的href属性,用日期作为下载的图片名字,用js模拟点击实现下载。

// 保存裁剪图片
		const saveImg = (e) => {
			if (img == null) {
				alert('请先上传图片')
				return
			}
			cropPreview.toBlob((blob) => {
                // 下载图片
				let a = document.createElement('a')
				a.href = window.URL.createObjectURL(blob)
				a.download = `${getDateStr(new Date())}.png` 
				a.dispatchEvent(new MouseEvent('click'))
			})
		}

完整代码

<!DOCTYPE html>
<html lang="en">
	<head>
		<meta charset="UTF-8" />
		<meta name="viewport" content="width=device-width, initial-scale=1.0" />
		<title>图片裁剪工具</title>
		<style>
			* {
				padding: 0;
				margin: 0;
			}

			#crop-tool {
				position: relative;
				overflow: hidden;
				width: 500px;
				height: 300px;
				margin: 100px auto;
				border: 1px solid black;
				border-radius: 15px;
			}
			#crop-img {
				z-index: -1;
				top: 0;
				left: 0;
				background: url('./img/mosaic.jpg');
			}

			#crop-cardbg {
				position: absolute;
				top: 0;
				left: 0;
			}
			#crop-modal {
				position: absolute;
				top: 0;
				left: 0;
			}
			#crop-clip {
				position: absolute;
				left: 25px;
				top: 37.1364px;
				cursor: all-scroll;
				width: 308.091px;
				height: 197.864px;
				border: 1px solid rgb(30, 158, 251);
			}

			#crop-modal {
				position: absolute;
				left: 0;
				top: 0;
				width: 500px;
				height: 300px;
				line-height: 300px;
				font-size: 30px;
				font-weight: 700;
				text-align: center;
				color: white;
				background-color: rgba(0, 0, 0, 0.5);
			}
			#crop-preview {
				border: 1px solid black;
				border-radius: 15px;
				width: 500px;
				height: 300px;
				margin: 0 700px;
			}

			#crop-but {
				width: 400px;
				margin: 0 auto;
			}
			button {
				width: 50px;
			}

			#crop-clip .dot {
				position: absolute;
				width: 20px;
				height: 20px;
				border-radius: 50%;
				background: #1e9efb;
			}

			#crop-clip .top-left {
				top: -10px;
				left: -10px;
				cursor: nwse-resize;
			}

			#crop-clip .top-right {
				top: -10px;
				right: -10px;
				cursor: nesw-resize;
			}

			#crop-clip .top-center {
				top: -10px;
				left: 50%;
				transform: translate(-50%);
				cursor: ns-resize;
			}

			#crop-clip .bottom-left {
				bottom: -10px;
				left: -10px;
				cursor: nesw-resize;
			}

			#crop-clip .bottom-center {
				bottom: -10px;
				left: 50%;
				transform: translate(-50%);
				cursor: ns-resize;
			}

			#crop-clip .bottom-right {
				bottom: -10px;
				right: -10px;
				cursor: nwse-resize;
			}

			#crop-clip .left-center {
				top: 50%;
				transform: translateY(-50%);
				left: -10px;
				cursor: ew-resize;
			}

			#crop-clip .right-center {
				top: 50%;
				transform: translateY(-50%);
				right: -10px;
				cursor: ew-resize;
			}
		</style>
		<!-- <link rel="stylesheet" href="./css/iconfont.css" /> -->
	</head>
	<body>
		<div id="crop-tool">
			<canvas id="crop-img" width="500" height="300"></canvas>
			<canvas id="crop-cardbg" width="500" height="300"></canvas>
			<div id="crop-clip" style="display: none">
				<div class="dot top-left"></div>
				<div class="dot top-right"></div>
				<div class="dot top-center"></div>
				<div class="dot bottom-left"></div>
				<div class="dot bottom-center"></div>
				<div class="dot bottom-right"></div>
				<div class="dot left-center"></div>
				<div class="dot right-center"></div>
			</div>
			<div id="crop-modal">请先上传图片</div>
		</div>
		<canvas id="crop-preview" width="500" height="300"> </canvas>
		<div id="crop-but">
			<input type="file" id="up-inp" name="文件上传" style="display: none" />
			<button type="button" id="up-but">上传</button>
			<button type="button" id="add-but">+</button>
			<button type="button" id="del-but">-</button>
			<button type="button" id="xzz-but">
				left
				<!-- <span class="iconfont icon-xiangzuoxuanzhuan"></span> -->
			</button>
			<button type="button" id="xyz-but">
				right
				<!-- <span class="iconfont icon-xiangyouxuanzhuan"></span> -->
			</button>

			<button type="button" id="save-but">截图</button>
		</div>
	</body>
	<script src="./js/Index.js"></script>
	<script>
		///
		 variable
		///

		// 按钮组
		let upBut = document.getElementById('up-but')
		let saveBut = document.getElementById('save-but')
		let addBut = document.getElementById('add-but')
		let delBut = document.getElementById('del-but')
		let xzzBut = document.getElementById('xzz-but')
		let xyzBut = document.getElementById('xyz-but')

		let upInp = document.getElementById('up-inp')

		let cropImg = document.querySelector('#crop-img') // 背景层
		let cropCardbg = document.querySelector('#crop-cardbg') // 裁剪层
		let cropPreview = document.querySelector('#crop-preview') // 裁剪层
		let cropModal = document.querySelector('#crop-modal') // 遮罩层
		let clip = document.getElementById('crop-clip') // 选择框

		let ctxCardbg = cropCardbg.getContext('2d')
		let ctxImg = cropImg.getContext('2d')
		let ctxPreview = cropPreview.getContext('2d')

		// 在canvas的裁剪框尺寸和坐标
		let selectCropObj = {
			x: 0,
			y: 0,
			w: 0,
			h: 0,
		}

		// 一开始存储到canvas的坐标尺寸和坐标
		let initImgObj = {
			// 主要是为了缩放/扩大图片用
			x: 0,
			y: 0,
			w: 0,
			h: 0,
		}
		let img = null
		let down = false // 中心拖拽或者按钮拖拽
		let angle = 0 // 旋转角度

		///
		 method
		///
		upBut.addEventListener('click', (e) => {
			upInp.click()
		})

		// 上传图片
		const updateFile = function (e) {
			let file = e.target.files[0]
			if (!file.type.startsWith('image')) {
				alert('只允许上传图片')
				return
			}
			const reader = new FileReader()
			reader.onload = (e) => {
				let img1 = new Image()
				img1.src = e.target.result
				img = img1

				img1.onload = (e) => {
					// 读取完毕之后
					selectCropObj = computeImage({
						imgWidth: img.width,
						imgHeight: img.height,
						width: cropCardbg.width,
						height: cropCardbg.height,
					})
					initImgObj = JSON.parse(JSON.stringify(selectCropObj))

					drawImage(initImgObj)
					drawModal()
					drawClip()
					drawClipDiv()
					imgPreview()
					cropModal.style.display = 'none'
					clip.style.display = 'block'
				}
			}
			reader.readAsDataURL(file)
		}

		upInp.addEventListener('change', updateFile)

		// 保存裁剪图片
		const saveImg = (e) => {
			if (img == null) {
				alert('请先上传图片')
				return
			}
			cropPreview.toBlob((blob) => {
				let a = document.createElement('a')
				a.href = window.URL.createObjectURL(blob)
				a.download = `${getDateStr(new Date())}.png`
				a.dispatchEvent(new MouseEvent('click'))
			})
		}

		saveBut.addEventListener('click', saveImg)

		// 图片预览
		const imgPreview = () => {
			ctxPreview.clearRect(0, 0, cropPreview.width, cropPreview.height)
			let { x, y, w, h } = selectCropObj
			let imgData = ctxImg.getImageData(x, y, w, h)
			ctxPreview.putImageData(imgData, x, y)
		}

		// 缩小/扩大图片

		const imgScale = (e, t) => {
			if (img == null) {
				alert('请先上传图片')
				return
			}
			let { w, h } = initImgObj

			if (t == 1) {
				// 缩小
				w = w / 2
				h = h / 2
			} else {
				// 扩大
				w = w * 2
				h = h * 2
			}

			// 重新求出,缩小,方法的图片坐标
			initImgObj = computeImage({
				imgWidth: w,
				imgHeight: h,
				width: cropImg.width,
				height: cropImg.height,
			})

			drawImage(initImgObj)
			imgPreview()
		}

		// 向右、左转(每次向左90度、向右90度)图片
		const imgRotate = (e, t = 1) => {
			if (img == null) {
				alert('请先上传图片')
				return
			}
			if (t == 1) {
				// 向右转,逆时针
				angle += -30 * (Math.PI / 180)
			} else {
				// 向左转,顺时针
				angle += 30 * (Math.PI / 180)
			}
			ctxImg.clearRect(0, 0, cropImg.width, cropImg.height)
			ctxImg.translate(cropImg.width / 2, cropImg.height / 2)
			ctxImg.rotate(angle)
			ctxImg.translate(-cropImg.width / 2, -cropImg.height / 2)
			drawImage(initImgObj)
			imgPreview()
		}

		delBut.addEventListener('click', (e) => {
			imgScale(e, 1)
		})

		addBut.addEventListener('click', (e) => {
			imgScale(e, 2)
		})

		xzzBut.addEventListener('click', (e) => {
			imgRotate(e, 1)
		})

		xyzBut.addEventListener('click', (e) => {
			imgRotate(e, 2)
		})

		// 画模版
		const drawModal = function () {
			ctxCardbg.clearRect(0, 0, cropCardbg.width, cropCardbg.height)
			ctxCardbg.fillStyle = 'rgba(0,0,0,0.5)'
			ctxCardbg.fillRect(0, 0, cropCardbg.width, cropCardbg.height)
		}

		// 计算图片在canvas实际坐标和尺寸
		const computeImage = function ({ imgWidth, imgHeight, width, height, base = 1 }) {
			if (imgWidth / base < width && imgHeight / base < height) {
				return {
					x: (width - imgWidth) / 2,
					y: (height - imgHeight) / 2,
					w: imgWidth / base,
					h: imgHeight / base,
				}
			}
			return computeImage({
				imgWidth,
				imgHeight,
				width,
				height,
				base: base + 0.1,
			})
		}

		// 画图像
		const drawImage = function ({ x, y, w, h }) {
			ctxImg.clearRect(0, 0, cropImg.width, cropImg.height)
			ctxImg.drawImage(img, x, y, w, h)
		}

		// 挖空
		const drawClip = function () {
			ctxCardbg.save()
			ctxCardbg.clearRect(selectCropObj.x, selectCropObj.y, selectCropObj.w, selectCropObj.h)
			ctxCardbg.restore()
		}

		// 挖空时,选择框的变化
		const drawClipDiv = () => {
			let cropClip = document.getElementById('crop-clip')
			cropClip.style.width = `${selectCropObj.w}px`
			cropClip.style.height = `${selectCropObj.h}px`
			cropClip.style.left = `${selectCropObj.x}px`
			cropClip.style.top = `${selectCropObj.y}px`
		}

		// 卡片拖拽事件,调用的方法(将选择框中央拖拽 ,和点拖拽一个方法处理)
		const carMouseMove = (e) => {
			// 两个都是false,证明我们一个没按下
			if (img === null) {
				return
			}

			if (!down) {
				return
			}

			let ele = e.target
			let { movementX, movementY } = e

			const isExistsCls = (_cls) => {
				for (let i = 0; i < ele.classList.length; i++) {
					const val = ele.classList[i]
					if (val === _cls) {
						return true
					}
				}
				return false
			}

			// 中央拖拽
			if (ele.id == 'crop-clip') {
				selectCropObj.x += movementX
				selectCropObj.y += movementY
				// 点拖拽
			} else if (isExistsCls('top-left')) {
				// 坐标和宽高的都要变
				selectCropObj.x += movementX
				selectCropObj.y += movementY
				selectCropObj.w += -movementX
				selectCropObj.h += -movementY
			} else if (isExistsCls('top-right')) {
				selectCropObj.y += movementY
				selectCropObj.w += movementX
				selectCropObj.h += -movementY
			} else if (isExistsCls('top-center')) {
				selectCropObj.y += movementY
				selectCropObj.h += -movementY
			} else if (isExistsCls('bottom-left')) {
				selectCropObj.x += movementX
				selectCropObj.y += movementY
				selectCropObj.w += -movementX
				selectCropObj.h += movementY
			} else if (isExistsCls('bottom-right')) {
				selectCropObj.w += movementX
				selectCropObj.h += movementY
			} else if (isExistsCls('bottom-center')) {
				selectCropObj.h += movementY
			} else if (isExistsCls('left-center')) {
				selectCropObj.x += movementX
				selectCropObj.w += -movementX
			} else if (isExistsCls('right-center')) {
				selectCropObj.w += movementX
			}

			drawClipDiv()
			drawModal()
			drawClip()
			imgPreview()
		}

		// 注册选择框拖拽事件
		const registerEvents = () => {
			// 注册那8个拖拽点事件
			const register = (_class) => {
				let node = document.querySelector(`.${_class}`)
				node.addEventListener('mousedown', (e) => {
					down = true
				})
				node.addEventListener('mousemove', carMouseMove)

				node.addEventListener('mouseup', function (e) {
					down = false
				})
			}

			register('top-center')
			register('bottom-center')
			register('left-center')
			register('right-center')
			register('bottom-right')
			register('bottom-left')
			register('top-right')
			register('top-left')

			// 注册拖拽中央移动的事件
			let clip = document.getElementById('crop-clip')
			clip.addEventListener('mousedown', (e) => {
				down = true
			})

			clip.addEventListener('mousemove', carMouseMove)

			clip.addEventListener('mouseup', (e) => {
				down = false
			})
		}

		registerEvents()
	</script>
</html>
const getDateStr = (time, tag1 = '-', tag2 = ':') => {
    const date = new Date(time)

    let y = date.getFullYear()
    let M = date.getMonth() + 1
    let d = date.getDate()
    let h = date.getHours()
    let m = date.getMinutes()
    let s = date.getSeconds()

    return `${y}${tag1}${M}${tag1}${d} ${h}${tag2}${m}${tag2}${s}`
}

文章来源:https://blog.csdn.net/Qhx20040819/article/details/135206345
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