实现微信小程序中的图片滤镜效果

<canvas canvas-id="myCanvas" style="width: 100%; height: 100%;"></canvas>

Page({
  onLoad: function() {
    var ctx = wx.createCanvasContext('myCanvas')

    wx.chooseImage({
      success: function(res) {
        var tempFilePaths = res.tempFilePaths

        ctx.drawImage(tempFilePaths[0], 0, 0, 300, 300)
        ctx.draw()
      }
    })
  }
})

Page({
  onLoad: function() {
    var ctx = wx.createCanvasContext('myCanvas')

    wx.chooseImage({
      success: function(res) {
        var tempFilePaths = res.tempFilePaths

        ctx.drawImage(tempFilePaths[0], 0, 0, 300, 300)

        // 应用滤镜效果
        ctx.filter = 'grayscale(100%)' // 灰度滤镜
        ctx.filter = 'sepia(100%)' // 褐色滤镜
        ctx.filter = 'blur(5px)' // 模糊滤镜

        // 绘制滤镜后的图像
        ctx.drawImage(tempFilePaths[0], 0, 0, 300, 300)

        ctx.draw()
      }
    })
  }
})

<view>
  <canvas canvas-id="myCanvas" style="width: 100%; height: 100%;"></canvas>
  <picker bindchange="changeFilter" value="{{currentFilterIndex}}" range="{{filterList}}" mode="selector">选择滤镜</picker>
</view>

Page({
  data: {
    filterList: ['无', '灰度', '褐色', '模糊'],
    currentFilterIndex: 0
  },

  onLoad: function() {
    // ...
  },

  changeFilter: function(e) {
    var index = e.detail.value

    var filter = ''

    switch (index) {
      case '1':
        filter = 'grayscale(100%)'
        break
      case '2':
        filter = 'sepia(100%)'
        break
      case '3':
        filter = 'blur(5px)'
        break
      default:
        filter = ''
    }

    var ctx = wx.createCanvasContext('myCanvas')
    // ...

    ctx.filter = filter
    // ...
  }
})