/* 选择颜色
 ob: 对象
 value：颜色值 */
 changeColor: function(e) {
  var value = e.target.dataset.value;
  if (this.data.ob && value) {
   wx.setStorageSync(this.data.ob, value);
   wx.navigateTo({
    url: '/pages/wallpaper/wallpaper',
   });
  }
 },

<template is="msgItem" data="{{...item}}"/> // 展开
<template is="msgItem" data="{{item}}"/>

// 生成图片
 drawPicture: function(val) {
  const that = this;
  const btnName = val.currentTarget.dataset.btnName;
  wx.canvasToTempFilePath({
   canvasId: 'myCanvas',
   success: function (res) {
    if (btnName === 'preview') {
     that.preview(res.tempFilePath);
    } else if (btnName === 'save') {
     that.save(res.tempFilePath);
    }
   },
   fail: function (err) {
    console.log(err);
   }
  })
 },

// 预览
 preview: function(val) {
  if(val) {
   wx.previewImage({
    urls: [val] // 需要预览的图片http链接列表
   })
  }
 },
// 保存
 save: function(val) {
  if(val) {
   wx.saveImageToPhotosAlbum({
    filePath: val,
    success: function (res) {
     console.log('成功');
    },
    fail: function (err) {
     console.log('失败', err);
     if (err.errMsg === "saveImageToPhotosAlbum:fail auth deny") {
      wx.openSetting({
       success(settingdata) {
        console.log(settingdata)
        if (settingdata.authSetting['scope.writePhotosAlbum']) {
         console.log('获取权限成功，给出再次点击图片保存到相册的提示。')
        } else {
         console.log('获取权限失败，给出不给权限就无法正常使用的提示')
        }
       }
      })
     }
    }
   });
  }
 },

// 裁减-换行(measureText)
  var lastSubStrIndex = 0;
  var dTextWidth = 0;
  var lineHeight = 20; // 行高
  var initX = 10; // 起始X坐标
  var initY = canvasHeight / 2; // 起始Y坐标
  for(var i = 0; i < dText.length; i++) {
   dTextWidth += ctx.measureText(dText[i]).width;
   if (dTextWidth > canvasWidth - initX) {
    ctx.fillText(dText.substring(lastSubStrIndex, i), initX, initY);
    initY += lineHeight;
    dTextWidth = 0;
    lastSubStrIndex = i;
   }
   if (i == dText.length-1) {
    ctx.fillText(dText.substring(lastSubStrIndex, i + 1), initX, initY);
   }
  }