微信小程序---通过二次贝塞尔曲线画波浪

淡淡的烟草味﹌ 2022-05-16 06:21 215阅读 0赞

*这两周做一个新的项目，人员比较紧张，除了需求和UI，前端后端一个人来干。*

*在项目需求确定后，UI隔了几天设计出了UI界面，拿到UI效果图后见有一个界面有波浪效果的我当时就蒙圈了，这都啥玩意啊？转念想到了最近在IT圈挺火的那个事件：产品要求安卓程序员实现根据用户手机壳颜色自动更换APP主题的需求后，顿时觉得画个波浪这个压根就不是事啊。*

## 二次贝塞尔曲线 ##

在微信官方的二次贝塞尔曲线画法连接如下：

[https://developers.weixin.qq.com/miniprogram/dev/api/canvas/quadratic-curve-to.html][https_developers.weixin.qq.com_miniprogram_dev_api_canvas_quadratic-curve-to.html]

## 画波浪 ##

思路：

在屏幕左边画一个波，然后让它一直向屏幕右边平移过去。其X的值由负数变为正数依次增大；然后一直重复此操作。

我画出来的波浪如下(感觉还是有那么一点波浪的感觉)：

![70][]

界面代码为(index.wxml)：

JS代码为(index.js)：

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)
      }
    })

[https_developers.weixin.qq.com_miniprogram_dev_api_canvas_quadratic-curve-to.html]: https://developers.weixin.qq.com/miniprogram/dev/api/canvas/quadratic-curve-to.html
[70]: /images/20220516/29df3bb5b2b64e48a8a74a597bafb6e1.png