demo.js

Page({
  onReady: function () {
    const cameraCtx = wx.createCameraContext()
    const cameraCfl = cameraCtx.onCameraFrame(res => {
      const data = new Uint8ClampedArray(res.data);
      wx.canvasPutImageData({
        x: 0,
        y: 0,
        width: 300,
        height: 150,
        data,
        success: res => {
          console.log('绘制成功：', res)
        },
        fail: res => {
          console.log('绘制失败：', res)
        },
        complete: res => {
          console.log(res)
        }
      })
    })
    cameraCfl.start()
  }
})

demo.wxml

demo.wxss

page{
  height: 100%;
}
.container {
  height: 100%;
}