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小程序?qū)崿F(xiàn)圖片預(yù)覽裁剪插件

更新時(shí)間：2019年11月22日 09:13:00 作者：aoaotheone

這篇文章主要為大家詳細(xì)介紹了小程序?qū)崿F(xiàn)圖片預(yù)覽裁剪插件，文中示例代碼介紹的非常詳細(xì)，具有一定的參考價(jià)值，感興趣的小伙伴們可以參考一下

最近在幫工作室做一個(gè)小程序，在換背景圖的時(shí)候需要預(yù)覽圖片，并且需要裁剪成固定的尺寸。因?yàn)樾〕绦虿⒉恢С衷膁om操作，導(dǎo)致很多現(xiàn)有的插件都無法使用，所以花了半天專門做了一個(gè)小程序的預(yù)覽裁剪插件。下面貼上代碼和效果圖。

wxml：

<canvas hidden='{{hide_canvas}}' id='cover-preview' bindtouchstart='canvas_start' bindtouchmove='canvas_move' bindtouchend='canvas_end' disable-scroll='true' canvas-id='cover-preview'>
  <cover-view catchtap='upload_bg' id='croper-sure'>確定</cover-view>
  <cover-view catchtap='cancel_croper' id='croper-cancel'>取消</cover-view>
  <cover-view id='croper'></cover-view>
 </canvas>

注意：canvas里面一定要用cover-view，否則無法覆蓋canvas

js：

const ctx = wx.createCanvasContext('cover-preview');
var start_position = {};//移動(dòng)圖片時(shí)手指起始坐標(biāo)
var tempFilePath;//圖片路徑
var tempWidth;//圖片初始寬度
var tempHeight;//圖片初始高度
var old_x = 0;//圖片初始x坐標(biāo)
var old_y = 0;//圖片初始y坐標(biāo)
var _touches = 1;//觸屏的手指數(shù)
var old_scale = 1;//原始放大倍數(shù)
var new_scale = 1;//新的放大倍數(shù)
var is_move = false;//是否移動(dòng)
var bg_url;
Page({
data: {
 hide_canvas:true,//繪圖層顯示控制變量
}，
//選擇并將圖片輸出到canvas
change_cover:function(){
  var that = this;
  wx.showModal({
   title: '提示',
   content: '更改我的封面',
   confirmColor: '#39bae8',
   success: function (res) {
    if (res.confirm) {
     
     
     wx.chooseImage({
      count: 1, // 默認(rèn)9
      sizeType: ['original', 'compressed'], // 可以指定是原圖還是壓縮圖，默認(rèn)二者都有
      sourceType: ['album', 'camera'], // 可以指定來源是相冊(cè)還是相機(jī)，默認(rèn)二者都有
      success: function (res0) {
       
       tempFilePath = res0.tempFilePaths[0];
       that.setData({
        hide_canvas: false,
        // edit_url: tempFilePath
       })
       wx.getImageInfo({
        src: tempFilePath,
        success: function (res) {
         // console.log(res.width)
         // console.log(res.height)
         tempWidth = res.width;
         tempHeight = res.height;
         ctx.drawImage(tempFilePath,0, 0, 375,res.height/res.width*375);
         ctx.draw();
        }
       })
       
      }
     })
    } else if (res.cancel) {
     console.log('用戶點(diǎn)擊取消')
    }
   }
  })
 },
 //監(jiān)聽手指觸摸事件，并判斷是移動(dòng)還是縮放，并記錄初始狀態(tài)
 canvas_start:function(e){
  // console.log(e);
  var touches = e.touches.length;
  if(touches == 1){
   _touches = 1;
   start_position = { x: e.touches[0].x, y: e.touches[0].y, timeStamp:e.timeStamp}
  }else if(touches == 2){
   _touches = 2;
   start_position = { x: e.touches[0].x, y: e.touches[0].y,x1: e.touches[1].x, y1: e.touches[1].y, timeStamp: e.timeStamp }
  }else{
   _touches = 1;
  }
 },
 //監(jiān)聽手指移動(dòng)事件，并做出相應(yīng)調(diào)整
 canvas_move: function (e) {
  // console.log(e);
  var touches = e.touches.length;
  if (_touches == 1 && e.timeStamp - start_position.timeStamp > 150) {
   ctx.drawImage(tempFilePath, old_x + e.touches[0].x - start_position.x, old_y + e.touches[0].y - start_position.y, 375 * new_scale, tempHeight / tempWidth * 375 * new_scale);
   ctx.draw();
   is_move = true;
  } else if (_touches == 2 && e.timeStamp - start_position.timeStamp > 150) {
   var change_x = Math.abs(Math.abs(e.touches[0].x - e.touches[1].x) - Math.abs(start_position.x - start_position.x1));
   var change_y = Math.abs(Math.abs(e.touches[0].y - e.touches[1].y) - Math.abs(start_position.y - start_position.y1));
   if(change_x - change_y > 10){
    old_scale = Math.abs(e.touches[0].x - e.touches[1].x) / Math.abs(start_position.x - start_position.x1);
   }else{
    old_scale = Math.abs(e.touches[0].y - e.touches[1].y) / Math.abs(start_position.y - start_position.y1);
   }
   ctx.drawImage(tempFilePath, old_x, old_y, 375 * old_scale * new_scale, tempHeight / tempWidth * 375 * old_scale * new_scale);
   ctx.draw();
   is_move = true;
  }else{
   is_move = false;
  }
 },
 //監(jiān)聽手指離開動(dòng)作，并保存當(dāng)前狀態(tài)數(shù)據(jù)
 canvas_end: function (e) {
  // console.log(e);
  if (_touches == 1 && is_move) {
   old_x = old_x + e.changedTouches[0].x - start_position.x;
   old_y = old_y + e.changedTouches[0].y - start_position.y;
  } else if (_touches == 2 && is_move) {
   new_scale = old_scale * new_scale;
  }
  
 },
 //確定并上傳背景圖
 upload_bg:function(){
  var that = this;
  var screenWidth = wx.getSystemInfoSync().screenWidth;
  // console.log(screenWidth);
  wx.canvasToTempFilePath({
   x: 0,
   y: screenWidth / 750 * 400,
   width: screenWidth,
   height: screenWidth / 750 * 526,
   destWidth: screenWidth,
   screenHeight: screenWidth / 750 * 526,
   quality:1,
   canvasId: 'cover-preview',
   success: function (res) {
    that.setData({
     hide_canvas: true,
    })
    //res.tempFilePath即為生成的圖片路徑
    console.log(res.tempFilePath)
    
   }
  })
 },
 //取消圖片預(yù)覽編輯
 cancel_croper:function(){
  ctx.clearActions();
  this.setData({
   hide_canvas: true,
   // edit_url: tempFilePath
  })
 },
})

wxss:

#cover-preview{
 width: 100%;
 height: 100%;
 background-color: black;
}
#croper{
 width: 750rpx;
 height: 526rpx;
 position: absolute;
 top: 400rpx;
 left: 0;
 background-color: rgba(135,206,250,0.5);
}
 
#croper-sure{
 width: 120rpx;
 height: 50rpx;
 border-radius: 10rpx;
 color: black;
 background-color: rgba(135,206,250,0.8);
 font-size: 40rpx;
 position: absolute;
 top: 946rpx;
 right: 10rpx;
 text-align: center
}
#croper-cancel{
 width: 120rpx;
 height: 50rpx;
 border-radius: 10rpx;
 color: black;
 background-color: rgba(135,206,250,0.8);
 font-size: 40rpx;
 position: absolute;
 top: 946rpx;
 right: 150rpx;
 text-align: center
}

效果圖