小程序图片选择区域/等屏裁剪实现方法

<view class="index_all_box">
	<view class="imgCut_header">
		<view class="imgCut_header_l" bindtap=‘okCutImg‘>开始裁剪</view>
		<view class="imgCut_header_m" bindtap=‘clickUpImg‘>点击上传图片</view>
		<view class="imgCut_header_r" bindtap=‘okBtn‘>点击确认</view>
	</view>
	<!-- 选择裁剪模式 -->
	<view class="selectCutMode" wx:if=‘{{alreay}}‘>
		<view class="selectCutMode_in {{cutType?‘selectCutMode_in_act‘:‘‘}}" bindtap=‘etcType‘>
			等屏裁剪
		</view>
		<view class="selectCutMode_in {{!cutType?‘selectCutMode_in_act‘:‘‘}}" bindtap=‘areaType‘>
			区域裁剪
		</view>
	</view>
	<view class="areaSelct_box" wx:if=‘{{!cutType && alreay}}‘>
		<slider bindchange="areaChange" min="50" max="100" show-value value=‘{{propor}}‘/>
	</view>
	<view class="cutImg_box" wx:if=‘{{!prienFlag}}‘>
		<view class="cutImg_box_t">
			<image src="{{cutImgUrl}}" mode=‘widthFix‘></image>
		</view>
		<view class="clickCutImg_txt" bindtap=‘againBtn‘>重新裁剪</view>
	</view>
	<view class="allCavans" wx:if=‘{{prienFlag}}‘ style=‘width: {{canvasW}}px;height: {{canvasH}}px‘ >
		<canvas class=‘canvasSty‘ style=‘width: {{canvasW}}px;height: {{canvasH}}px‘ canvas-id=‘cutImg‘ disable-scroll=‘true‘ bindtouchmove=‘canvasMove‘></canvas>
		<view class="allCavans_inbg"  style=‘width: {{canvasW}}px;height:{{canvasH}}px; background: url({{img}});background-size: 100% 100%‘></view>
	</view>
	
	
</view>

.imgCut_header{
	padding: 30rpx;
	display: flex;
	justify-content: space-between;
	align-items: center;
	background: #000;
	color: #fff;
	font-size: 24rpx;
}
.allCavans{
	margin: 20rpx auto;
	position: relative;
}
.canvasSty{
	position: absolute;
}
.cutImg_box{
	width: 100%;
	
	border-bottom: 2rpx #f98700 solid;
	padding-bottom: 20rpx;
}
.cutImg_box .cutImg_box_t{
	width: 90%;
	margin: 20rpx auto;
}
.cutImg_box image{
	width: 100%;
}
.cutImg_box .cutImg_box_b{
	margin-top: 20rpx;
	width: 80%;
	height: 80rpx;
	line-height: 80rpx;
	background: #f98700;
	color: #fff;
	border-radius: 10rpx;
	text-align: center;
	margin:0rpx auto;
}
.selectCutMode{
	background: #fff;
	display: flex;
	justify-content: space-between;
	align-items: center;
}
.selectCutMode .selectCutMode_in{
	width: 100%;
	text-align: center;
	background: #fff;
	color: #f98700;
	font-size: 24rpx;
	padding: 20rpx;
}
.selectCutMode .selectCutMode_in_act{
	background: #f98700;
	color: #fff;
	padding: 20rpx;
}
.areaSelct_box{
	width: 100%;
	display: flex;
	align-items: center;
	height: 50rpx;
	justify-content: center;
	margin-top: 20rpx;
}
.areaSelct_box slider{
	width: 80%;
}
.cutImg_box .clickCutImg_txt{
	width: 100%;
	text-align: center;
	height: 50rpx;
	font-size: 24rpx;
	line-height: 50rpx;
	color: #999;
}

onLoad: function (options) {
    var that = this;
    const ctx = wx.createCanvasContext(‘cutImg‘);
    ctx.setGlobalAlpha(0.4)
    var aa = ‘https://pintuanqu.oss-cn-hangzhou.aliyuncs.com/Uploads/Picture/goodsShow/20171201/5a2125fc86566.png‘
　　//获取当前屏幕宽度
    var phoneW = Number(util.nowPhoneWH()[0]*90)/100;
    var cutH = 150;
    wx.getImageInfo({
      src: aa,
      success: function (res) {
        var w = phoneW;
        var h = (phoneW/Number(res.width))*Number(res.height)
        ctx.save() 
        ctx.drawImage(aa, 0, 0, w, h)
        ctx.restore()
        ctx.setFillStyle(‘red‘)
        ctx.fillRect(0, 0, phoneW, cutH)
        ctx.draw()
        that.setData({
          canvasW:w,
          canvasH:h,
          img:aa,
          cutH:cutH
        })
      }
    })
  },

// 点击确认裁剪图片
  okCutImg:function(){
    var that = this;
    var canvasW = that.data.canvasW;
    var canvasH = that.data.canvasH;
    var nowCutW = that.data.cutType?canvasW:that.data.nowCutW;
    var nowCutH = that.data.cutType?that.data.cutH:that.data.nowCutH;
    var cutX = that.data.cutX;
    var cutY = that.data.cutY;
    const ctx = wx.createCanvasContext(‘cutImg‘);
    ctx.setGlobalAlpha(1)
    ctx.drawImage(that.data.img, 0, 0, canvasW, canvasH)
    ctx.draw()
    wx.canvasToTempFilePath({
      x: cutX,
      y: cutY,
      width: nowCutW,
      height: nowCutH,
      destWidth: nowCutW,
      destHeight: nowCutH,
      canvasId: ‘cutImg‘,
      success: function(res) {
        var aa = res.tempFilePath
        that.setData({
          cutImgUrl:aa,
          prienFlag:false,
          alreay:false
        })
      } 
    })
  },

// 点击红框开始移动
  canvasMove:function(e){
    var that = this;
    var canvasW = that.data.canvasW;
    var canvasH = that.data.canvasH;
    var nowCutW = that.data.cutType?canvasW:that.data.nowCutW;
    var nowCutH = that.data.cutType?that.data.cutH:that.data.nowCutH
    var touches = e.touches[0];   
    var x = touches.x;
    var y = touches.y-(Number(nowCutH)/2);
    that.data.cutType?x=0:x=x-(Number(nowCutW)/2);
    that.setData({
      cutX:x,
      cutY:y
    })
    const ctx = wx.createCanvasContext(‘cutImg‘);
    ctx.setGlobalAlpha(0.4)
    ctx.drawImage(that.data.img, 0, 0, canvasW, canvasH)
    ctx.setFillStyle(‘red‘)
    ctx.fillRect(x, y, nowCutW, nowCutH)
    ctx.draw()
  },

//等屏裁剪
  etcType:function(){
    var that = this;
    var propor = 100;
    var canvasW = that.data.canvasW;
    var canvasH = that.data.canvasH;
    var cutH = that.data.cutH;
    var nowCutW = (Number(canvasW)*propor)/100
    var nowCutH = (Number(cutH)*propor)/100
    const ctx = wx.createCanvasContext(‘cutImg‘);
    ctx.setGlobalAlpha(0.4)
    ctx.drawImage(that.data.img, 0, 0, canvasW, canvasH)
    ctx.setFillStyle(‘red‘)
    ctx.fillRect(0, 0, nowCutW, nowCutH)
    ctx.draw()
    that.setData({
      nowCutW:nowCutW,
      nowCutH:nowCutH,
      cutType:true
    })
  },

areaType:function(){
    var that = this;
    var propor = that.data.propor;
    var canvasW = that.data.canvasW;
    var canvasH = that.data.canvasH;
    var cutH = that.data.cutH;
    var nowCutW = (Number(canvasW)*propor)/100
    var nowCutH = (Number(cutH)*propor)/100
    const ctx = wx.createCanvasContext(‘cutImg‘);
    ctx.setGlobalAlpha(0.4)
    ctx.drawImage(that.data.img, 0, 0, canvasW, canvasH)
    ctx.setFillStyle(‘red‘)
    ctx.fillRect(0,0, nowCutW, nowCutH)
    ctx.draw()
    that.setData({
      nowCutW:nowCutW,
      nowCutH:nowCutH,
      cutType:false
    })
  },

areaChange:function(e){
    var that = this;
    var propor = e.detail.value;
    var canvasW = that.data.canvasW;
    var canvasH = that.data.canvasH;
    var cutH = that.data.cutH;
    var nowCutW = (Number(canvasW)*propor)/100
    var nowCutH = (Number(cutH)*propor)/100
    const ctx = wx.createCanvasContext(‘cutImg‘);
    ctx.setGlobalAlpha(0.4)
    ctx.drawImage(that.data.img, 0, 0, canvasW, canvasH)
    ctx.setFillStyle(‘red‘)
    ctx.fillRect(that.data.cutX||0, that.data.cutY||0,nowCutW, nowCutH)
    ctx.draw()
    that.setData({
      nowCutW:nowCutW,
      nowCutH:nowCutH,
      propor:propor
    })
  },

// 重新裁剪
  againBtn:function(){
    var that = this;
    var data = that.data
    this.setData({
      prienFlag:true,
      alreay:true
    })
    const ctx = wx.createCanvasContext(‘cutImg‘);
    ctx.setGlobalAlpha(0.4)
    ctx.drawImage(data.img, 0, 0, data.canvasW, data.canvasH)
    ctx.setFillStyle(‘red‘)
    ctx.fillRect(that.data.cutX||0, that.data.cutY||0, data.nowCutW||data.canvasW, data.nowCutH||data.cutH)
    ctx.draw()
  },