工作中公司業務需要的微信小程序用戶簽字功能

先看效果圖：

wxml：

<view class="wrapper">
  <view class="handBtn">
    <image catchtap="selectColorEvent" src="{{ selectColor === ‘black‘ ? ‘../../images/color_black_selected.png‘ : ‘../../images/color_black.png‘ }}" class="{{ selectColor === ‘black‘ ? ‘color_select‘ : ‘‘ }} black-select"
 
 data-color="black"
      data-color-value="#1A1A1A"></image>
    <image catchtap="selectColorEvent" src="{{ selectColor === ‘red‘ ? ‘../../images/color_red_selected.png‘ : ‘../../images/color_red.png‘ }}" class="{{ selectColor === ‘red‘ ? ‘color_select‘ : ‘‘ }} red-select" data-color="red"
      data-color-value
 
="#ca262a"></image>
    <button catchtap="retDraw" class="delBtn">重寫</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">手寫板</view>
  </view>
</view>

上面代碼中所用的圖片資源：

color_black.png

color_black_selected.png

color_red.png

color_red_selected.png

js

data:

  data: {
    canvasName: ‘handWriting‘,
    ctx: ‘‘,
    canvasWidth: 0,
    canvasHeight: 0,
    transparent: 1, // 透明度
    selectColor: ‘black‘,
    lineColor: ‘#1A1A1A‘, // 顏色
    lineSize: 1.5,  // 筆記倍數
    lineMin: 0.5,   // 最小筆畫半徑
    lineMax: 4,     // 最大筆畫半徑
    pressure: 1,     // 默認壓力
    smoothness: 60,  //順滑度，用60的距離來計算速度
    currentPoint: {},
    currentLine: [],  // 當前線條
    firstTouch: true, // 第一次觸發
    radius: 1, //畫圓的半徑
    cutArea: { top: 0, right: 0, bottom: 0, left: 0 }, //裁剪區域
    bethelPoint: [],  //保存所有線條 生成的貝塞爾點；
    lastPoint: 0,
    chirography: [], //筆跡
    currentChirography: {}, //當前筆跡
    linePrack: [] //劃線軌跡 , 生成線條的實際點
  },

初始化:

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

事件函數

筆跡開始

  // 筆跡開始
  uploadScaleStart (e) {
    if (e.type != ‘touchstart‘) return false;
    let ctx = this.data.ctx;
    ctx.setFillStyle(this.data.lineColor);  // 初始線條設置顏色
    ctx.setGlobalAlpha(this.data.transparent);  // 設置半透明
    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);
  },

筆跡移動

  // 筆跡移動
  uploadScaleMove (e) {
    if (e.type != ‘touchmove‘) return false;
    if (e.cancelable) {
      // 判斷默認行為是否已經被禁用
      if (!e.defaultPrevented) {
        e.preventDefault();
      }
    }
    let point = {
      x: e.touches[0].x,
      y: e.touches[0].y
    }

    //測試裁剪
    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);
  },

筆跡結束

  // 筆跡結束
  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));
    }
    //一筆結束，保存筆跡的坐標點，清空，當前筆跡
    //增加判斷是否在手寫區域；
    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: []
    })
  },

其他函數：

 retDraw () {
    this.data.ctx.clearRect(0, 0, 700, 730)
    this.data.ctx.draw()
  },

  //畫兩點之間的線條；參數為:line，會繪制最近的開始的兩個點；
  pointToLine (line) {
    this.calcBethelLine(line);
    return;
  },
  //計算插值的方式；
  calcBethelLine (line) {
    if (line.length <= 1) {
      line[0].r = this.data.radius;
      return;
    }
    let x0, x1, x2, y0, y1, y2, r0, r1, r2, len, lastRadius, dis = 0, time = 0, curveValue = 0.5;
    if (line.length <= 2) {
      x0 = line[1].x
      y0 = line[1].y
      x2 = line[1].x + (line[0].x - line[1].x) * curveValue;
      y2 = line[1].y + (line[0].y - line[1].y) * curveValue;
      //x2 = line[1].x;
      //y2 = line[1].y;
      x1 = x0 + (x2 - x0) * curveValue;
      y1 = y0 + (y2 - y0) * curveValue;;

    } else {
      x0 = line[2].x + (line[1].x - line[2].x) * curveValue;
      y0 = line[2].y + (line[1].y - line[2].y) * curveValue;
      x1 = line[1].x;
      y1 = line[1].y;
      x2 = x1 + (line[0].x - x1) * curveValue;
      y2 = y1 + (line[0].y - y1) * curveValue;
    }
    //從計算公式看，三個點分別是(x0,y0),(x1,y1),(x2,y2) ；(x1,y1)這個是控制點，控制點不會落在曲線上；實際上，這個點還會手寫獲取的實際點，卻落在曲線上
    len = this.distance({ x: x2, y: y2 }, { x: x0, y: y0 });
    lastRadius = this.data.radius;
    for (let n = 0; n < line.length - 1; n++) {
      dis += line[n].dis;
      time += line[n].time - line[n + 1].time;
      if (dis > this.data.smoothness) break;
    }
    this.setData({
      radius: Math.min(time / len * this.data.pressure + this.data.lineMin, this.data.lineMax) * this.data.lineSize
    });
    line[0].r = this.data.radius;
    //計算筆跡半徑；
    if (line.length <= 2) {
      r0 = (lastRadius + this.data.radius) / 2;
      r1 = r0;
      r2 = r1;
      //return;
    } else {
      r0 = (line[2].r + line[1].r) / 2;
      r1 = line[1].r;
      r2 = (line[1].r + line[0].r) / 2;
    }
    let n = 5;
    let point = [];
    for (let i = 0; i < n; i++) {
      let t = i / (n - 1);
      let x = (1 - t) * (1 - t) * x0 + 2 * t * (1 - t) * x1 + t * t * x2;
      let y = (1 - t) * (1 - t) * y0 + 2 * t * (1 - t) * y1 + t * t * y2;
      let r = lastRadius + (this.data.radius - lastRadius) / n * i;
      point.push({ x: x, y: y, r: r });
      if (point.length == 3) {
        let a = this.ctaCalc(point[0].x, point[0].y, point[0].r, point[1].x, point[1].y, point[1].r, point[2].x, point[2].y, point[2].r);
        a[0].color = this.data.lineColor;
        // let bethelPoint = this.data.bethelPoint;
        // console.log(a)
        // console.log(this.data.bethelPoint)
        // bethelPoint = bethelPoint.push(a);
        this.bethelDraw(a, 1);
        point = [{ x: x, y: y, r: r }];
      }
    }
    this.setData({
      currentLine: line
    })
  },
  //求兩點之間距離
  distance (a, b) {
    let x = b.x - a.x;
    let y = b.y - a.y;
    return Math.sqrt(x * x + y * y);
  },
  ctaCalc (x0, y0, r0, x1, y1, r1, x2, y2, r2) {
    let a = [], vx01, vy01, norm, n_x0, n_y0, vx21, vy21, n_x2, n_y2;
    vx01 = x1 - x0;
    vy01 = y1 - y0;
    norm = Math.sqrt(vx01 * vx01 + vy01 * vy01 + 0.0001) * 2;
    vx01 = vx01 / norm * r0;
    vy01 = vy01 / norm * r0;
    n_x0 = vy01;
    n_y0 = -vx01;
    vx21 = x1 - x2;
    vy21 = y1 - y2;
    norm = Math.sqrt(vx21 * vx21 + vy21 * vy21 + 0.0001) * 2;
    vx21 = vx21 / norm * r2;
    vy21 = vy21 / norm * r2;
    n_x2 = -vy21;
    n_y2 = vx21;
    a.push({ mx: x0 + n_x0, my: y0 + n_y0, color: "#1A1A1A" });
    a.push({ c1x: x1 + n_x0, c1y: y1 + n_y0, c2x: x1 + n_x2, c2y: y1 + n_y2, ex: x2 + n_x2, ey: y2 + n_y2 });
    a.push({ c1x: x2 + n_x2 - vx21, c1y: y2 + n_y2 - vy21, c2x: x2 - n_x2 - vx21, c2y: y2 - n_y2 - vy21, ex: x2 - n_x2, ey: y2 - n_y2 });
    a.push({ c1x: x1 - n_x2, c1y: y1 - n_y2, c2x: x1 - n_x0, c2y: y1 - n_y0, ex: x0 - n_x0, ey: y0 - n_y0 });
    a.push({ c1x: x0 - n_x0 - vx01, c1y: y0 - n_y0 - vy01, c2x: x0 + n_x0 - vx01, c2y: y0 + n_y0 - vy01, ex: x0 + n_x0, ey: y0 + n_y0 });
    a[0].mx = a[0].mx.toFixed(1);
    a[0].mx = parseFloat(a[0].mx);
    a[0].my = a[0].my.toFixed(1);
    a[0].my = parseFloat(a[0].my);
    for (let i = 1; i < a.length; i++) {
      a[i].c1x = a[i].c1x.toFixed(1);
      a[i].c1x = parseFloat(a[i].c1x);
      a[i].c1y = a[i].c1y.toFixed(1);
      a[i].c1y = parseFloat(a[i].c1y);
      a[i].c2x = a[i].c2x.toFixed(1);
      a[i].c2x = parseFloat(a[i].c2x);
      a[i].c2y = a[i].c2y.toFixed(1);
      a[i].c2y = parseFloat(a[i].c2y);
      a[i].ex = a[i].ex.toFixed(1);
      a[i].ex = parseFloat(a[i].ex);
      a[i].ey = a[i].ey.toFixed(1);
      a[i].ey = parseFloat(a[i].ey);
    }
    return a;
  },
  bethelDraw (point, is_fill, color) {
    let ctx = this.data.ctx;
    ctx.beginPath();
    ctx.moveTo(point[0].mx, point[0].my);
    if (undefined != color) {
      ctx.setFillStyle(color);
      ctx.setStrokeStyle(color);
    } else {
      ctx.setFillStyle(point[0].color);
      ctx.setStrokeStyle(point[0].color);
    }
    for (let i = 1; i < point.length; i++) {
      ctx.bezierCurveTo(point[i].c1x, point[i].c1y, point[i].c2x, point[i].c2y, point[i].ex, point[i].ey);
    }
    ctx.stroke();
    if (undefined != is_fill) {
      ctx.fill(); //填充圖形 ( 後繪制的圖形會覆蓋前面的圖形, 繪制時註意先後順序 )
    }
    ctx.draw(true)
  },
  selectColorEvent (event) {
    console.log(event)
    var color = event.currentTarget.dataset.colorValue;
    var colorSelected = event.currentTarget.dataset.color;
    this.setData({
      selectColor: colorSelected,
      lineColor: color
    })
  }

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: 250rpx;
  left: 0rpx;
  transform: rotate(90deg);
  color: #666;
}

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

.subBtn {
  position: absolute;
  bottom: 52rpx;
  left: -3rpx;
  display: inline-flex;
  transform: rotate(90deg);
  background: #008ef6;
  color: #fff;
  margin-bottom: 30rpx;
  text-align: center;
  justify-content: center;
}

.black-select {
  width: 60rpx;
  height: 60rpx;
  position: absolute;
  top: 30rpx;
  left: 25rpx;
}
.black-select.color_select {
  width: 90rpx;
  height: 90rpx;
  top: 30rpx;
  left: 10rpx;
}
.red-select {
  width: 60rpx;
  height: 60rpx;
  position: absolute;
  top:140rpx;
  left:25rpx;
}
.red-select.color_select {
  width: 90rpx;
  height: 90rpx;
  top: 120rpx;
  left: 10rpx;
}

github地址：https://github.com/momtboy/handwriting-weapp

備用地址（拉取的作者的）：https://github.com/Ta0hua/handwriting-weapp

轉載：https://www.jianshu.com/p/84dcc0adfe44

【微信小程序canvas】實現小程序手寫板用戶簽名(附代碼)