话不多说，直接上代码

1、页面布局

<view class="buttons" style="height: 50px;"><view class="upload btn" style="background-color: #d18118;"bindtap="uploadImage"> 上传图片 </view><viewclass="getCropperImage btn"style="background-color: #04b00f;"bindtap="getCropperImage">生成图片</view>
</view>
<view class="canvas"><canvas style="width: {{canvasWidth}}px;height: {{canvasHeight}}px;"type="2d" id="canvas-1" canvas-id="canvas-1"disable-scroll="true"></canvas><canvas style="width: {{canvasWidth}}px;height: {{canvasHeight}}px;position: absolute;top: 0;z-index: 999;"type="2d" id="canvas-2" disable-scroll="true"bindtouchstart="touchStart"bindtouchmove="touchMove"bindtouchend="touchEnd"></canvas>
</view>

2、页面样式

page{padding: 0;-webkit-user-select: none;user-select: none;width: 100%;height: 100%;background-color: #c0c0c0;font-family: Arial, Helvetica, sans-serif;overflow-x: hidden;
}
.buttons{display: flex;flex-direction: row;justify-content: space-between;align-items: center;padding: 0 25rpx;border-bottom: 1rpx solid white;
}
.canvas{position: relative;
}

3、页面逻辑

let ctx = null;
let canvas = null;
Page({data: {canvasWidth:300,canvasHeight:500,pixelRatio:2,pointRadius:12,// 裁剪框边角原点半径point:[[48,48],[312, 48],[312, 224],[48, 224]],// 裁剪框边角原点位置moveIndex:-1//点击的剪切框原点小标},onLoad (options) {const that = this;wx.getSystemInfo({success (res) {that.setData({canvasWidth:res.windowWidth,canvasHeight:res.windowHeight -50,pixelRatio: res.pixelRatio,})}})},uploadImage(){const that = this;wx.chooseMedia({count: 1,mediaType: ['image','video'],sourceType: ['album', 'camera'],maxDuration: 30,camera: 'back',success(res) {that.drawImage(res.tempFiles[0].tempFilePath);}})},drawImage(src){const self = this;wx.getImageInfo({src: src,success (res) {const width = self.data.canvasWidth;const height = self.data.canvasHeight;var innerAspectRadio = res.width / res.height;//图片宽高比var customAspectRadio = width / height;//画布宽高比let x = 0;let y = 0;let baseWidth = 0;//图片在画布宽度let baseHeight = 0;//图片在画布高度if (innerAspectRadio > customAspectRadio) {baseWidth = width*0.8;baseHeight = (width / innerAspectRadio)*0.8;} else {baseWidth = height * innerAspectRadio;baseHeight = height;}x = (width-baseWidth)/2;y = (height-baseHeight)/2;// 绘制图片wx.createSelectorQuery().select('#canvas-1').fields({ node: true, size: true }).exec((res) => {// Canvas 对象const canvas = res[0].node// 渲染上下文const ctx = canvas.getContext('2d');// 初始化画布大小const dpr = self.data.pixelRatiocanvas.width = width * dprcanvas.height = height * dprctx.scale(dpr, dpr)// 开始绘制let image = canvas.createImage();//创建iamge实例image.src = src;  //引入图片image.onload = function () {ctx.drawImage(image, x, y, baseWidth, baseHeight);self.setData({point:[[x-10,y-10],[x+baseWidth+10,y-10],[x+baseWidth+10,y+baseHeight+10],[x-10,y+baseHeight+10]]},()=>{self.pointInit()})}})}})},pointInit(){const that = this;const query = wx.createSelectorQuery()query.select('#canvas-2').fields({ node: true, size: true }).exec((res) => {// Canvas 对象const canvas = res[0].nodethat.canvas = canvas;// 渲染上下文const ctx = canvas.getContext('2d');that.ctx = ctx;// 初始化画布大小const dpr = that.data.pixelRatiocanvas.width = that.data.canvasWidth * dprcanvas.height = that.data.canvasHeight * dprctx.scale(dpr, dpr)// 开始绘制that.drawPoint(that.data.point)})},drawPoint(point){const ctx = this.ctx;const pointRadius = this.data.pointRadius;ctx.clearRect(0, 0, this.data.canvasWidth, this.data.canvasHeight)ctx.beginPath()ctx.fillStyle = 'rgb(0, 0, 200)';ctx.arc(point[0][0], point[0][1], pointRadius, 0, 2*Math.PI , true)ctx.arc(point[1][0], point[1][1], pointRadius, 0, 2*Math.PI , true)ctx.fill()ctx.beginPath()ctx.arc(point[2][0], point[2][1], pointRadius, 0, 2*Math.PI , true)ctx.arc(point[3][0], point[3][1], pointRadius, 0, 2*Math.PI , true)ctx.fill()ctx.beginPath()ctx.lineWidth = 4ctx.strokeStyle = 'rgba(255,255,255,0.6)';ctx.lineJoin = 'round'ctx.lineCap = 'round'ctx.lineTo(point[0][0], point[0][1])ctx.lineTo(point[1][0], point[1][1])ctx.lineTo(point[2][0], point[2][1])ctx.lineTo(point[3][0], point[3][1])ctx.lineTo(point[0][0], point[0][1])ctx.stroke()ctx.fillStyle = 'rgb(0, 0, 0, 0.5)';ctx.fill()},//  手势初始监测touchStart: function touchStart (e) {var that = this;var ref = e.touches[0];const point = this.data.point;const pointRadius = this.data.pointRadius;let moveIndex = -1;for(var i=0;i<4;i++){if(ref.x > (point[i][0]-pointRadius) && ref.x < (point[i][0]+pointRadius)){if(ref.y > (point[i][1]-pointRadius) && ref.y < (point[i][1]+pointRadius)){moveIndex = i;break;}}}if(moveIndex!=-1){that.setData({moveIndex:moveIndex})}},//  手势滑动touchMove: function touchMove (e) {var ref = e.touches[0];var x = ref.x;var y = ref.y;if(this.data.moveIndex!=-1){const point = this.data.point;const index = this.data.moveIndex;point[index][0] = x;point[index][1] = y;this.setData({point:point},()=>{this.drawPoint(point);})}},// 手势滑动结束touchEnd: function touchEnd (e) {var ref = e.changedTouches[0];var x = ref.x;var y = ref.y;if(this.data.moveIndex!=-1){const point = this.data.point;const index = this.data.moveIndex;point[index][0] = x;point[index][1] = y;this.setData({point:point,moveIndex:-1})}},getCropperImage(){const self = this;const point = this.data.point;wx.createSelectorQuery().select('#canvas-1').fields({ node: true, size: true }).exec((res) => {// Canvas 对象const canvas = res[0].node// 渲染上下文const ctx = canvas.getContext('2d');// 初始化画布大小// const dpr = self.data.pixelRatio// canvas.width = self.data.windowWidth * dpr// canvas.height = self.data.windowHeight * dpr// ctx.scale(dpr, dpr)// // 开始绘制// ctx.beginPath()// ctx.moveTo(point[0][0], point[0][1]);// ctx.lineTo(point[1][0], point[1][1]);// ctx.lineTo(point[2][0], point[2][1]);// ctx.lineTo(point[3][0], point[3][1]);// ctx.lineTo(point[0][0], point[0][1]);// //先关闭绘制路径。注意，此时将会使用直线连接当前端点和起始端点。// ctx.closePath();// ctx.fill()// ctx.clip()debuggerwx.canvasToTempFilePath({x: 0,y: 0,width: 200,height: 200,destWidth: 200,destHeight: 200,canvasId: 'canvas-1',success: function (res) {debuggerconsole.log(res.tempFilePath)},fail: function (res) {debuggerconsole.log(res)},},this)})}
})