微信小程序生成用户带自己二维码的海报

 效果图

• wxml

<canvas class="canvas-poster" id="canvasPoster" canvas-id="canvasPoster"></canvas>

<image src="{
  {poster}}" style="width: 500rpx; height: 889rpx;"></image>

• 下载海报背景图片

  
  downloadBGImg: function (phoneNumber) {
    var that = this;
    wx.downloadFile({
      //服务器图片地址
      url: "你服务器IP/bj.png",
      success: function (res) {
        console.log(res);
        var rr = res.tempFilePath;
        that.shareInfo.bgImg = rr;
        //下载中间的二维码
        that.downloadInviteImg(phoneNumber,true);
      }
    })
  },

• 下载用户二维码图片

  
  downloadInviteImg: function (phoneNumber,flag) {
    var that = this;
    wx.downloadFile({
      //用户二维码图片,我是用每个用户的电话号码分类图片
      url:phoneNumber + ".png",
      success: function (res) {
        console.log(res);
        if (res.statusCode == 200) {
          var rr = res.tempFilePath;
          that.shareInfo.qrcode = rr;
          var query = wx.createSelectorQuery()
          query.select('#canvasPoster').boundingClientRect((res) => {
            //绘制海报
            that.drawImage(res)
          }).exec();
        } else {
          if(flag==true){
            //用户二维码图片是从腾讯服务器那边下载然后存到本地的服务器，所以用户第一次请求二维码图    
            //片时，本地服务器是没有的，调用此方法将二维码图片下载到本地服务器
            that.getQrcode(phoneNumber);
          }
        }

      }
    })
  },

• 绘制海报

       
 drawImage(canvasAttrs) {
    var that = this;
    wx.getSystemInfo({
      success(res) {
        // 通过像素比计算出画布的实际大小（330x490）是展示的出来的大小
        that.systemInfo = res
      }
    })
    let ctx = wx.createCanvasContext('canvasPoster', this)
    let canvasW = canvasAttrs.width // 画布的真实宽度
    let canvasH = canvasAttrs.height //画布的真实高度
    let headerW = 48 * this.systemInfo.pixelRatio
    let qrcodeW = 300
    let qrcodeX =  (canvasW - qrcodeW)/2 //定位到中间
    let qrcodeY = canvasH/14*8
    // 填充背景
    ctx.drawImage(this.shareInfo.bgImg, 0, 0, canvasW, canvasH)
    ctx.save()
    ctx.drawImage(this.shareInfo.qrcode, qrcodeX, qrcodeY, qrcodeW, qrcodeW)
    ctx.save()
    //绘制邀请文字  此处的邀请码是显示在二维码下方的，用户二维码本身是带有同样邀请码的(服务器完成)
    let msg="邀请码 : "+this.data.myInviteCode;
    //计算文本长度
    ctx.setFontSize(30);
    let msgLength=ctx.measureText(msg).width;
    let textWidth= (canvasW - msgLength)/2 ;
    let textHeight = canvasH/15*13
      //绘制文字背景 =>圆角矩形
      this.roundRect(ctx,textWidth-20, textHeight-42.5, msgLength+35, 60,35,'#dd555a');
      ctx.setFillStyle('#ffffff');
      //绘制文字
    ctx.fillText(msg, textWidth, textHeight)
    ctx.draw()
    setTimeout(() => {
      wx.canvasToTempFilePath({
        canvasId: 'canvasPoster',
        x: 13,
        y: 13,
        width: canvasW - 26,
        height: canvasH - 26,
        destWidth: canvasW - 26,
        destHeight: canvasH - 26,
        success: (res) => {
          that.setData({
            poster: res.tempFilePath,
            showBoxView: true
          })
          wx.hideLoading();
        }
      })
    }, 200)
  },

 
roundRect(ctx, x, y, w, h, r, c = '#fff') {
  if (w < 2 * r) { r = w / 2; }
  if (h < 2 * r) { r = h / 2; }

  ctx.beginPath();
  ctx.fillStyle = c;

  ctx.arc(x + r, y + r, r, Math.PI, Math.PI * 1.5);
  ctx.moveTo(x + r, y);
  ctx.lineTo(x + w - r, y);
  ctx.lineTo(x + w, y + r);

  ctx.arc(x + w - r, y + r, r, Math.PI * 1.5, Math.PI * 2);
  ctx.lineTo(x + w, y + h - r);
  ctx.lineTo(x + w - r, y + h);

  ctx.arc(x + w - r, y + h - r, r, 0, Math.PI * 0.5);
  ctx.lineTo(x + r, y + h);
  ctx.lineTo(x, y + h - r);

  ctx.arc(x + r, y + h - r, r, Math.PI * 0.5, Math.PI);
  ctx.lineTo(x, y + r);
  ctx.lineTo(x + r, y);

  ctx.fill();
  ctx.closePath();
},