【微信小程序canvas】实现小程序手写板用户签名(附代码)

工作中公司业务需要的微信小程序用户签字功能

先看效果图：

demo

wxml

<view class="wrapper">
  <view class="handBtn">
    <button catchtap="retDraw" class="delBtn">重写</button>
    <button catchtap="subCanvas" class="subBtn">完成</button> 
  </view>
  <view class="handCenter">
    <canvas class="handWriting" disable-scroll="true" bindtouchstart="uploadScaleStart" bindtouchmove="uploadScaleMove"
      bindtouchend="uploadScaleEnd" bindtap="mouseDown" canvas-id="handWriting">
    </canvas>
  </view>
  <view class="handRight">
    <view class="handTitle">手写板</view>
  </view>
</view>

js

data

page({
    data: {
        canvasName: 'handWriting',
        ctx: '',
        canvasWidth: 0,
        canvasHeight: 0,
        transparent: 1, // 透明度
        selectColor: 'black',
        lineColor: '#1A1A1A', // 颜色
        lineSize: 1.5,  // 笔记倍数
        lineMin: 0.5,   // 最小笔画半径
        lineMax: 4,     // 最大笔画半径
        pressure: 1,     // 默认压力
        smoothness: 60,  //顺滑度，用60的距离来计算速度
        currentPoint: {},
        currentLine: [],  // 当前线条
        firstTouch: true, // 第一次触发
        radius: 1, //画圆的半径
        cutArea: { top: 0, right: 0, bottom: 0, left: 0 }, //裁剪区域
        bethelPoint: [],  //保存所有线条 生成的贝塞尔点；
        lastPoint: 0,
        chirography: [], //笔迹
        currentChirography: {}, //当前笔迹
        linePrack: [], //划线轨迹 , 生成线条的实际点
    }
})

初始化

page({
  onLoad () {
    let canvasName = this.data.canvasName
    let ctx = wx.createCanvasContext(canvasName)
    this.setData({
      ctx: ctx
    })
    var query = wx.createSelectorQuery();
        query.select('.handCenter').boundingClientRect(rect => {query.select('.handCenter').boundingClientRect(rect => {
          this.setData({this.setData({
            canvasWidth: rect.width,canvasWidth: rect.width,
            canvasHeight: rect.heightcanvasHeight: rect.height
          })})
        }).exec(); }).exec();
      }, },
})

事件函数

笔迹开始

// 笔迹开始
  uploadScaleStart (e) {
    if (e.type != 'touchstart') return false;
    let ctx = this.data.ctx;
    ctx.setFillStyle(this.data.lineColor);  // 初始线条设置颜色
    ctx.setGlobalAlpha(this.data.transparent);  // 设置半透明
    let currentPoint = {
      x: e.touches[0].x,
      y: e.touches[0].y
    }
    let currentLine = this.data.currentLine;
    currentLine.unshift({
      time: new Date().getTime(),
      dis: 0,
      x: currentPoint.x,
      y: currentPoint.y
    })
    this.setData({
      currentPoint,
      // currentLine
    })
    if (this.data.firstTouch) {
      this.setData({
        cutArea: { top: currentPoint.y, right: currentPoint.x, bottom: currentPoint.y, left: currentPoint.x },
        firstTouch: false
      })
    }
    this.pointToLine(currentLine);
  },

笔迹移动

// 笔迹移动
  uploadScaleMove (e) {
    if (e.type != 'touchmove') return false;
    if (e.cancelable) {
      // 判断默认行为是否已经被禁用
      if (!e.defaultPrevented) {
        e.preventDefault();
      }
    }
    let point = {
      x: e.touches[0].x,
      y: e.touches[0].y
    }

    //测试裁剪
    if (point.y < this.data.cutArea.top) {
      this.data.cutArea.top = point.y;
    }
    if (point.y < 0) this.data.cutArea.top = 0;

    if (point.x > this.data.cutArea.right) {
      this.data.cutArea.right = point.x;
    }
    if (this.data.canvasWidth - point.x <= 0) {
      this.data.cutArea.right = this.data.canvasWidth;
    }
    if (point.y > this.data.cutArea.bottom) {
      this.data.cutArea.bottom = point.y;
    }
    if (this.data.canvasHeight - point.y <= 0) {
      this.data.cutArea.bottom = this.data.canvasHeight;
    }
    if (point.x < this.data.cutArea.left) {
      this.data.cutArea.left = point.x;
    }
    if (point.x < 0) this.data.cutArea.left = 0;

    this.setData({
      lastPoint: this.data.currentPoint,
      currentPoint: point
    })
    let currentLine = this.data.currentLine
    currentLine.unshift({
      time: new Date().getTime(),
      dis: this.distance(this.data.currentPoint, this.data.lastPoint),
      x: point.x,
      y: point.y
    })
    // this.setData({
    //   currentLine
    // })
    this.pointToLine(currentLine);
  },

笔迹结束

// 笔迹结束
  uploadScaleEnd (e) {
    if (e.type != 'touchend') return 0;
    let point = {
      x: e.changedTouches[0].x,
      y: e.changedTouches[0].y
    }
    this.setData({
      lastPoint: this.data.currentPoint,
      currentPoint: point
    })
    let currentLine = this.data.currentLine
    currentLine.unshift({
      time: new Date().getTime(),
      dis: this.distance(this.data.currentPoint, this.data.lastPoint),
      x: point.x,
      y: point.y
    })
    // this.setData({
    //   currentLine
    // })
    if (currentLine.length > 2) {
      var info = (currentLine[0].time - currentLine[currentLine.length - 1].time) / currentLine.length;
      //$("#info").text(info.toFixed(2));
    }
    //一笔结束，保存笔迹的坐标点，清空，当前笔迹
    //增加判断是否在手写区域；
    this.pointToLine(currentLine);
    var currentChirography = {
      lineSize: this.data.lineSize,
      lineColor: this.data.lineColor
    };
    var chirography = this.data.chirography
    chirography.unshift(currentChirography);
    this.setData({
      chirography
    })
    var linePrack = this.data.linePrack
    linePrack.unshift(this.data.currentLine);
    this.setData({
      linePrack,
      currentLine: []
    })
  },

wxss

page {
  background: #fbfbfb;
  height: auto;
  overflow: hidden;
}

.wrapper {
  width: 100%;
  height: 95vh;
  margin: 30rpx 0;
  overflow: hidden;
  display: flex;
  align-content: center;
  flex-direction: row;
  justify-content: center;
  font-size: 28rpx;
}

.handWriting {
  background: #fff;
  width: 100%;
  height: 95vh;
}

.handRight {
  display: inline-flex;
  align-items: center;
}

.handCenter {
  border: 4rpx dashed #e9e9e9;
  flex: 5;
  overflow: hidden;
  box-sizing: border-box;
}

.handTitle {
  transform: rotate(90deg);
  flex: 1;
  color: #666;
}

.handBtn button {
  font-size: 28rpx;
}

.handBtn {
  height: 95vh;
  display: inline-flex;
  flex-direction: column;
  justify-content: space-between;
  align-content: space-between;
  flex: 1;
}

.delBtn {
  position: absolute;
  top: 550rpx;
  left: 0rpx;
  transform: rotate(90deg);
  color: #666;
}

.delBtn image {
  position: absolute;
  top: 13rpx;
  left: 25rpx;
}

结语

详细项目代码handwriting-weapp（微信小程序原生canvas用户签字手写板，后续更新计划组件化、优化渲染逻辑、增加功能，欢迎start 和 PR)