微信小程序 压缩图片并上传

转自https://segmentfault.com/q/1010000012507519

 

wxml写入

<view bindtap='uploadImg'>上传</view>
 <image bindtap='uploadImg' data-number="0" src="{{ uploadPic[0] }}" alt="" mode="widthFix"></image>
<canvas style="width: {{cw}}px; height: {{ch}}px;" canvas-id="firstCanvas"></canvas>

　　

JS参考

 

 uploadImg(e) {
    let that = this;
    console.log(e);
    let index = e.currentTarget.dataset.number;
    let uploadFile = ''; //最后处理完，图片上传的图片地址
    wx.chooseImage({
      success(res) {
        console.log(res)
        const tempFilePaths = res.tempFilePaths;

        //获得原始图片大小
        wx.getImageInfo({
          src: res.tempFilePaths[0],
          success(res) {
            // console.log('获得原始图片大小',res.width)
            //console.log(res.height)
            var originWidth, originHeight;
            originHeight = res.height;
            originWidth = res.width;
            console.log(originWidth);
            //压缩比例
            // 最大尺寸限制
            var maxWidth = 1200,
              maxHeight = 600;
            // 目标尺寸
            var targetWidth = originWidth,
              targetHeight = originHeight;
            //等比例压缩，如果宽度大于高度，则宽度优先，否则高度优先
            if (originWidth > maxWidth || originHeight > maxHeight) {
              if (originWidth / originHeight > maxWidth / maxHeight) {
                // 要求宽度*(原生图片比例)=新图片尺寸
                targetWidth = maxWidth;
                targetHeight = Math.round(maxWidth * (originHeight / originWidth));
              } else {
                targetHeight = maxHeight;
                targetWidth = Math.round(maxHeight * (originWidth / originHeight));
              }
            }
            //尝试压缩文件，创建 canvas
            var ctx = wx.createCanvasContext('firstCanvas');//当在组件里使用时，要使用var ctx = wx.createCanvasContext('firstCanvas',that); that是this的变量
            ctx.clearRect(0, 0, targetWidth, targetHeight);
            ctx.drawImage(tempFilePaths[0], 0, 0, targetWidth, targetHeight);
            ctx.draw();
            //更新canvas大小
            that.setData({
              cw: targetWidth,
              ch: targetHeight
            });
            //保存图片
            setTimeout(function() {
              wx.canvasToTempFilePath({
                canvasId: 'firstCanvas',
                success: (res) => {
                  //写入图片数组
                  var uploadpic = "uploadPic[" + index + "]";
                  //
                  that.setData({
                    [uploadpic]: res.tempFilePath
                  });
                  uploadFile = res.tempFilePath;
                  //保存到相册
                  // wx.saveImageToPhotosAlbum({
                  //   filePath: res.tempFilePath,
                  //   success: (res) => {
                  //     console.log(res)
                  //   },
                  //   fail: (err) => {
                  //     console.error(err)
                  //   }
                  // })
                  wx.uploadFile({
                    url: 'https://example.weixin.qq.com/upload', //仅为示例，非真实的接口地址
                    filePath: uploadFile,
                    name: 'file',
                    formData: {
                      'user': 'test'
                    },
                    success(res) {
                      const data = res.data
                      //do something
                    }
                  })
                },
                fail: (err) => {
                  console.error(err)
                }
              }, this)//注意这里this是否指向正确，that?
            }, 500);




          }
        })




      }
    })
  }

　　

后面还有一个写法 20210703

 

 // 上传图片

  async chooseImg() {

    var _that = this;

    const imgs = this.data.imgs;

    const max_imgs_length = 1;

    var oldCount = imgs.length;

    const tempFilePaths = await this.$chooseImage(max_imgs_length, ['original']);

    for (var i = 0; i < tempFilePaths.length; i++) {

      // imgs.push(tempFilePaths[i]); 

      var tfp = tempFilePaths[i];

       

      //获得原始图片大小

      wx.getImageInfo({

        src: tfp,

        success(res) {

          var originWidth, originHeight;

          originHeight = res.height;

          originWidth = res.width;

          console.log(originWidth);

          //压缩比例

          // 最大尺寸限制

          var maxWidth = 1200,

            maxHeight = 1000;

          // 目标尺寸

          var targetWidth = originWidth,

            targetHeight = originHeight;

          //等比例压缩，如果宽度大于高度，则宽度优先，否则高度优先

          if (originWidth > maxWidth || originHeight > maxHeight) {

            if (originWidth / originHeight > maxWidth / maxHeight) {

              // 要求宽度*(原生图片比例)=新图片尺寸

              targetWidth = maxWidth;

              targetHeight = Math.round(maxWidth * (originHeight / originWidth));

            } else {

              targetHeight = maxHeight;

              targetWidth = Math.round(maxHeight * (originWidth / originHeight));

            }

          }

          _that.setData({

            cw: targetWidth,

            ch: targetHeight

          });

          //尝试压缩文件，创建 canvas

          var ctx = wx.createCanvasContext('ssd');

          ctx.clearRect(0, 0, targetWidth, targetHeight);

          ctx.drawImage(tfp, 0, 0, targetWidth, targetHeight);

          ctx.draw(false, setTimeout(function () { 

            wx.canvasToTempFilePath({

              canvasId: 'ssd',

              fileType:'jpg',

              destWidth:targetWidth,

              destHeight:targetHeight,

              quality:1.0,

              success: (r) => { 

                imgs.push(r.tempFilePath);

                _that.setData({

                  imgs: imgs

                });

               _that.loadPhoto(oldCount);

              },

              fail: (err) => {

                console.error(err)

              }

            }, this)

          }, 500));

          //保存图片 

        }

      })

    } 

  }

 

 

wx.createCanvasContext()停止维护，可用下面方法代替

let canvasBox = null;

// 写法一
canvasBox = wx.createCanvasContext("ssd");
// 写法二
wx.createSelectorQuery()
      .select("#ssd")
      .context(function (res) {
        console.log("节点实例：", res); // 节点对应的 Canvas 实例。
        canvasBox = res.context;
      })

　　

 

前端隱藏canvas

  <view  style="position:fixed;top:999999999999999999999rpx;">

    <canvas id="ssd" canvas-id="ssd" style="width:{{cw}}px;height:{{ch}}px;"></canvas>

    </view>