小程序canvas手写签名适配PC实现示例详解

// pages/mine/signature/drawCanvas/drawCanvas.js
var app = getApp()
Page({
  data: {
    context: null,
    index: 0,
    height: 0,
    width: 0,
    // 前 一点
    preX: 0,
    preY: 0,
    preCenterX: 0,
    preCenterY: 0
  },
  onShow: function () {
    let query = wx.createSelectorQuery();
    const that = this;
    query.select('#firstCanvas').boundinGClientRect();
    query.exec(function (rect) {
      let width = rect[0].width;
      let height = rect[0].height;
      that.setData({
        width,
        height
      });
      const context = wx.createCanvasContext('firstCanvas')
      that.setData({
        context: context
      })
      context.setStrokeStyle('#000000')
      context.setLineWidth(2)
      context.setFontSize(20)
    });
  },
  
  bindtouchstart: function (e) {
    let context = this.data.context
    let curX = e.changedTouches[0].x
    let curY = e.changedTouches[0].y
    context.beginPath()
    context.moveTo(curX, curY)
    this.data.preX = curX
    this.data.preY = curY
    this.data.preCenterX = curX
    this.data.preCenterY = curY
  },
  
  bindtouchmove: function (e) {
    let context = this.data.context
    let preX = this.data.preX
    let preY = this.data.preY
    let preCenterX = this.data.preCenterX
    let preCenterY = this.data.preCenterY
    let curX = e.changedTouches[0].x
    let curY = e.changedTouches[0].y
    let deltaX = Math.abs(preX - curX)
    let deltaY = Math.abs(preY - curY)
    // 相差大于3像素的时候作二阶贝塞尔曲线
    if (deltaX >= 3 || deltaY >= 3) {
      // 前后两点中心点
      let centerX = (preX + curX) / 2
      let centerY = (preY + curY) / 2
      //这里以前一点作为控制点，中心点作为终点，起始点为上一次的中点，很流畅啊！
      context.moveTo(preCenterX, preCenterY)
      context.quadraticCurveTo(preX, preY, centerX, centerY);
      context.stroke();
      context.draw(true);
      this.data.preX = curX
      this.data.preY = curY
      this.data.preCenterX = centerX
      this.data.preCenterY = centerY
    }
  },
  
  clear: function () {
    let context = this.data.context
    context.clearRect(0, 0, this.data.width, this.data.height);
    context.draw();
    context.setStrokeStyle('#000000')
    context.setLineWidth(2)
    context.setFontSize(20)
  },
  
  export: function () {
    const that = this;
    this.data.context.draw(false, wx.canvasToTempFilePath({
      x: 0,
      y: 0,
      width: that.data.width,
      height: that.data.height,
      destWidth: that.data.width,
      destHeight: that.data.height,
      fileType: 'png',
      canvasId: 'firstCanvas',
      success(res) {
        app.log("tempFilePath:" + res.tempFilePath);
		// 你的代码
      },
      fail() {
        wx.showToast({
          title: '提交失败',
          icon: 'none',
          duration: 2000
        })
      }
    }))
  },
})

wx.getSystemInfo({
      success:function(res){
        that.setData({
          systemInfo:res,
        })
        if(res.platfORM == "devtools"){
            //开发者工具
        }else if(res.platform == "iOS"){
            //IOS
        }else if(res.platform == "Android"){
            //android
        }else {
        	//电脑了吧
        }
      }
    })