微信小程序使用二次贝塞尔曲线画波浪

<view class="page-body">
 <view class="page-body-wrapper">
  <canvas canvas-id="myCanvas3" class="canvas3"></canvas>
 </view>
</view>

Page({
 onReady: function() {
  this.position = {
    x: 150,
    y: 150,
    vx: 2,
    vy: 2
   },
   this.obj = {
    offset: 0,
    baseLine: 40,
    direction: 1,
    waveDirection: 1
   },
   // var offset = 5
   this.drawQuadraticCurve3()
  this.interval = setInterval(this.drawQuadraticCurve3, 1)
  console.log(">>>>>>>>>" + this.obj.offset)
 },
 /
   画大波浪
  /
 drawQuadraticCurve3: function() {
  var obj = this.obj
  var startX = 20,
   itemWidth = 100,
   offset = obj.offset,
   baseLine = obj.baseLine,
   waveHeight = 10,
   direction = obj.direction,
   waveDirection = obj.waveDirection
 
  const ctx = wx.createCanvasContext('myCanvas3')
 
 
  function getWaveHeigh(i) {
   if (i % 2 == 0) {
    // return baseLine + waveHeight
   }
   return baseLine - waveHeight
  }
  ctx.beginPath()
  ctx.moveTo(-itemWidth  6, baseLine)
  ctx.setFillStyle('#4BF6EE')
  for (var i = -6; i < 5; i++) {
   startX = i  itemWidth;
   var currentX = startX + (itemWidth / 2) + offset
   var currentY = getWaveHeigh(i)
   var currentEndX = startX + itemWidth + offset
   ctx.quadraticCurveTo(currentEndX - 10,
    currentY, currentEndX, baseLine)
   ctx.stroke()
  }
  //填充海水
  ctx.lineTo(0, 2000)
  ctx.setFillStyle('#4BF6EE')
  ctx.fill()
 
  ctx.draw()
 
 
  if (obj.waveDirection == 1) {
   obj.offset = obj.offset + 1
  } else if (obj.waveDirection == -1) {
   obj.offset = obj.offset - 1
  }
  if (obj.offset == 400) {
   obj.offset = 0
  }
  if (obj.offset == 50 || obj.offset == 1) {
   // obj.waveDirection = obj.waveDirection  -1
  }
 
 
  // if (direction == 1) {
  //  obj.baseLine = obj.baseLine + 1
  // } else if (direction == -1) {
  //  obj.baseLine = obj.baseLine - 1
  // }
  if (obj.baseLine >= 50 || obj.baseLine <= 40) {
   console.log("<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<")
   //obj.direction = (obj.direction  -1)
  }
 },
 onUnload: function() {
  clearInterval(this.interval)
 }
})