wx.getImageInfo({ src: tempFilePaths, success: function (res) { const SIZE = 300 const ratio = Math.max((res.width/SIZE)*1, (res.height/SIZE)*1, 1) const smallWidth = Math.trunc(res.width / ratio) const smallHeight = Math.trunc(res.height / ratio) console.log('宽度：',smallWidth) console.log('高度：',smallHeight) console.log('缩放比例:',ratio) const ctx = wx.createCanvasContext('photo_canvas'); ctx.drawImage(tempFilePaths, 0, 0, smallWidth, smallHeight); ctx.draw(false, function () { wx.canvasToTempFilePath({ width: smallWidth, height: smallHeight, destWidth: smallWidth, destHeight: smallHeight, canvasId: 'photo_canvas', success: function (res) { var filePaths = res.tempFilePath wx.getFileSystemManager().unlink({ filePath: res.tempFilePath, success: function(res) { console.log('删除临时图片成功') // 清空画布 const ctx = wx.createCanvasContext('photo_canvas'); ctx.clearRect(0, 0, canvasWidth, canvasHeight) }, fail: function(res) { console.log('删除临时图片失败', res) } })这段代码中删除临时图片是失败的为什么？

根据你提供的代码，可能是因为在删除临时图片之前，清空画布的代码有误。在清空画布时，你使用了未定义的 `canvasWidth` 和 `canvasHeight` 变量。你需要先定义这两个变量，或者直接使用 `smallWidth` 和 `smallHeight` 变量来清空画布。

修改后的代码如下：

wx.getImageInfo({
  src: tempFilePaths,
  success: function (res) {
    const SIZE = 300
    const ratio = Math.max((res.width/SIZE)*1, (res.height/SIZE)*1, 1)
    const smallWidth = Math.trunc(res.width / ratio)
    const smallHeight = Math.trunc(res.height / ratio)
    console.log('宽度：',smallWidth)
    console.log('高度：',smallHeight)
    console.log('缩放比例:',ratio)
    const ctx = wx.createCanvasContext('photo_canvas');
    ctx.drawImage(tempFilePaths, 0, 0, smallWidth, smallHeight);
    ctx.draw(false, function () {
      wx.canvasToTempFilePath({
        width: smallWidth,
        height: smallHeight,
        destWidth: smallWidth,
        destHeight: smallHeight,
        canvasId: 'photo_canvas',
        success: function (res) {
          var filePaths = res.tempFilePath
          wx.getFileSystemManager().unlink({
            filePath: res.tempFilePath,
            success: function(res) {
              console.log('删除临时图片成功')
              // 清空画布
              const ctx = wx.createCanvasContext('photo_canvas');
              ctx.clearRect(0, 0, smallWidth, smallHeight)
            },
            fail: function(res) {
              console.log('删除临时图片失败', res)
            }
          })
        }
      })
    })
  }
})

请注意，如果删除临时图片的问题还未解决，你可以在控制台输出 `res` 对象来查看具体的错误信息，以便更好地定位问题。