微信小程序绘制canvas图片

1.效果图

2.注意事项

1.https网址图片需要预先下载到本地用wx.downloadFile方法
2.wx.downloadFile需要在微信公众号后台配置域名才能获取图片，如图：

3.代码

1.wxml

canvas.wxml

<cover-view bindtap='savePic'>
        <canvas style="width:100%;height:{{contentHeight}}px"   canvas-id="myCanvas" bindlongpress="savePic"> 
            
            
        </canvas>
  </cover-view>
  <button bindtap='savePic' class="buttonStyle">预览并发送</button>

2.js代码

  1.图片需要先下载到本地，并保存本地图片路径，包括头像，头像图片的域名同样要在后台配置，不然发布线上获取不到。

canvas.js

var util = require('../../utils/md5.js');
var tool = require('../../utils/base64tool.js')
var app = new getApp();

//canvas.js
Page({
  data: {
    windowWidth: 0, //屏幕宽度
    windowHeight: 0,//屏幕高度
    contentHeight: 0,//内容高度
    thinkList: [], //文字超出换行处理
    lineHeight: 30, //固定值
    contentTitle: "我的昵称", //我的昵称
    canvasUrl: "", //canvasurl
    qrCode: "", //小程序码https图片路径
    goodsInfoImg: "",  //海报图片
    specText: "京东社交电商合作伙伴", //京东社交电商合作伙伴
    userIcon:""//微信头像
  },

  onLoad: function (options) {

    let that = this;

    that.getQr();
    // 查看是否授权
    wx.getSetting({
      success(res) {
        if (res.authSetting['scope.userInfo']) {
          // 已经授权，可以直接调用 getUserInfo 获取头像昵称
          wx.getUserInfo({
            success(resInfo) {
              that.setData({ contentTitle: resInfo.userInfo.nickName})
              wx.downloadFile({
                url: resInfo.userInfo.avatarUrl,
                success(downloadRes) {
                  if (downloadRes.statusCode === 200) {
                    that.setData({
                      userIcon: downloadRes.tempFilePath
                    })
                  }
                }
              })
            }
          })
        } else {
          that.setData({
            userIcon: '/img/noperson.png'
          })
        }
      }
    })

  





   






    //获取设备信息高度。计算出其他的高度等
    wx.getSystemInfo({
      success: function (res) {
        that.setData({
          windowWidth: res.windowWidth,
          windowHeight: res.windowHeight,
          normalPageX:
            res.windowWidth * 0.045, //左边文本图片X轴位置
          boxWidth: res.windowWidth * 0.91, //分享图片box宽度
          boxheight: res.windowHeight, //分享图片box高度
          boxPageY: res.windowWidth * 0.2, //boxY轴位置
          imgWidth: res.windowWidth * 0.91, //海报图片宽度
          imgHeight: res.windowHeight * 0.82, //海报图片高度
          imgPageY: res.windowWidth * 0, //海报图片Y轴位置
          userIconWidth: res.windowWidth * 0.162,//头像图片宽度
          userIconHeight: res.windowWidth * 0.162,//头像图片高度
          userIconPageY: res.windowHeight * 0.82 + 15,//头像Y轴位置
          codeWidth: res.windowWidth * 0.25, //小程序码图片宽度
          codeHeight: res.windowWidth * 0.25, //小程序码图片高度
          codePageY: res.windowHeight * 0.80, //小程序码Y轴位置
          avatarPageY: res.windowHeight * 0.82 + 15, //头像Y轴位置
          titlePageY: res.windowHeight * 0.82 + 25, //微信昵称Y轴位置
          specPageY: res.windowHeight * 0.82 + 42, //京东社交Y轴位置
        });
      }
    });
    //网络图片转为本地图片，直接显示网络图片的话真机不显示
   // that.getTempFile("cloud://luer-f3ipn.6c75-luer-f3ipn-1301025398/6684e5652d611c27b5895a6911e51b7.png");
    that.getTempFile(app.globeData.shareCodeImg); 
  },
//获取小程序码
  getQr: function () {
    var that = this;
    var phone = wx.getStorageSync('phone');
    var apiKey = '[e-mail]￥%GFYLCL#*WLMinPro!!;';
    var time = Date.parse(new Date());
    var sign = util.hexMD5(apiKey + time);
    apiKey = util.hexMD5(apiKey);
    var url = app.globeData.host + 'minPro/getShareMinCode?sign=' + sign + '&apiKey=' + apiKey + '&time=' + time + '&phone=' + phone;
    that.setData({
      qrCode: url
    })
  },



  //临时图片路径
  getTempFile: function (url) {
    wx.showLoading({
    });
    let that = this;
    wx.cloud.downloadFile({
      fileID: url,
      success: function (res) {
        console.log("res.tempFilePath===>", res.tempFilePath)
        that.setData({
          goodsInfoImg: res.tempFilePath
        });
        //继续生成商品的小程序码
        that.downloadSkuQrCode(that.data.qrCode);
      },
      fail: function (err) { }
    });
  },
  getData: function () {
    let that = this;

    let i = 0;
    let lineNum = 1;
    let thinkStr = "";
    let thinkList = [];
    for (let item of that.data.contentTitle) {
      if (item === "\n") {
        thinkList.push(thinkStr);
        thinkList.push("a");
        i = 0;
        thinkStr = "";
        lineNum += 1;
      } else if (i === 21) {
        thinkList.push(thinkStr);
        i = 1;
        thinkStr = item;
        lineNum += 1;
      } else {
        thinkStr += item;
        i += 1;
      }
    }
    thinkList.push(thinkStr);
    that.setData({
      thinkList: thinkList
    });
    that.createNewImg(lineNum);
  },

  //画矩形，也是整块画布的大小，宽度是屏幕宽度，高度根据内容多少来动态设置。
  drawSquare: function (ctx, height) {
    let that = this;
    ctx.rect(
      that.data.windowWidth * 0.045,
      that.data.boxPageY,
      that.data.boxWidth,
      height
    );
    ctx.setFillStyle("#fff");
    ctx.fill();
  },

  // 设置文字大小，并填充颜色。
  drawFont: function (ctx, contentTitle, height) {
    let that = this;
    let str = that.data.contentTitle;
    let firstline;
    let secondline;
    //一行显示12个字，超过一行时
    if (str.length > 11) {
      //第一行截取前14个字符
      firstline = str.substring(0, 11);
    } else {
      //一行就能显示时候
      firstline = str;
    }
    //填充微信昵称
    ctx.setFontSize(14);
    ctx.setFillStyle("#000");
    ctx.fillText(firstline, that.data.normalPageX + that.data.userIconWidth+20, that.data.titlePageY+10);

    //填充京东社交合作伙伴
    if (that.data.specText) {
      ctx.setFontSize(12);
      ctx.setFillStyle("#999999");
      ctx.fillText(
        that.data.specText,
        that.data.normalPageX + that.data.userIconWidth+20,
        that.data.specPageY + 18
      );
    }
  },
  // 根据文字多少动态计算高度，然后依次画出矩形，文字，横线和小程序码。
  createNewImg: function (lineNum) {
    let that = this;
    let ctx = wx.createCanvasContext("myCanvas");
    let contentHeight = that.data.boxheight;
    that.drawSquare(ctx, contentHeight);
    that.setData({
      contentHeight: contentHeight
    });
    let height = 100;
    for (let item of that.data.thinkList) {
      if (item !== "a") {
        that.drawFont(ctx, item, height);
        height += that.data.lineHeight;
      }
    }
    //海报图片
    ctx.drawImage(
      that.data.goodsInfoImg,
      that.data.normalPageX,
      that.data.imgPageY,
      that.data.imgWidth,
      that.data.imgHeight
    );

   //画圆形
    ctx.save();
    ctx.beginPath(); //开始绘制
    ctx.arc(that.data.userIconWidth / 2 + 28, that.data.userIconWidth / 2 + that.data.userIconPageY, that.data.userIconWidth / 2, 0, Math.PI * 2, false);
    ctx.clip();
    //头像
    ctx.drawImage(
      that.data.userIcon,
      that.data.normalPageX+10,
      that.data.userIconPageY,
      that.data.userIconWidth,
      that.data.userIconHeight
    );
    ctx.restore();
    // 填充小程序码
    ctx.drawImage(
      that.data.qrCode,
      that.data.normalPageX + that.data.windowWidth * 0.65,
      that.data.codePageY,
      that.data.codeWidth,
      that.data.codeHeight
    );
    // 长按分享给好友
    ctx.setFillStyle("#333");
    ctx.font = "normal normal 9px sans-serif";
    ctx.fillText(
      "长按分享",
      that.data.normalPageX +
      that.data.windowWidth * 0.65 +
      that.data.codeWidth/3,
      that.data.codePageY + that.data.codeWidth + 10
    );
    ctx.draw(); //绘制到canvas
  },

  // 保存图片
  savePic: function () {
    let that = this;
    wx.canvasToTempFilePath({
      x: 0,
      y: 50,
      width: that.data.windowWidth * 2,
      height: that.data.contentHeight * 2,
      canvasId: "myCanvas",
      success: function (res) {
        // util.savePicToAlbum(res.tempFilePath);
        wx.hideLoading();
        var tempFilePath = res.tempFilePath;
        that.setData({
          canvasUrl: tempFilePath
        });
        if (tempFilePath !== "") {
          wx.hideLoading();
          wx.previewImage({
            current: that.data.canvasUrl, // 当前显示图片的http链接
            urls: [that.data.canvasUrl], // 需要预览的图片http链接列表
            success: function (_res) {
              console.log("预览成功啦");
            }
          });
        }
      }
    });
  },
  //下载小程序码
  downloadSkuQrCode: function (url) {
    let that = this;
    wx.downloadFile({
      url: url,
      success: function (res) {
        that.setData({
          qrCode: res.tempFilePath
        });
        wx.hideLoading();
        //生成数据
        that.getData();
      },
      fail: function (err) {
        wx.showToast({
          title: "下载小程序码失败,稍后重试！",
          icon: "none",
          duration: 5000
        });
      }
    });
  },

  //点击保存到相册
  saveShareImg: function () {
    var that = this;
    wx.showLoading({
      title: '正在保存',
      mask: true,
    })
    setTimeout(function () {
      wx.canvasToTempFilePath({
        canvasId: 'myCanvas',
        success: function (res) {
          wx.hideLoading();
          var tempFilePath = res.tempFilePath;
          wx.saveImageToPhotosAlbum({
            filePath: tempFilePath,
            success(res) {
              // utils.aiCardActionRecord(19);
              wx.showModal({
                content: '图片已保存到相册，赶紧晒一下吧~',
                showCancel: false,
                confirmText: '好的',
                confirmColor: '#333',
                success: function (res) {
                  if (res.confirm) { }
                },
                fail: function (res) { }
              })
            },
            fail: function (res) {
              wx.showToast({
                title: res.errMsg,
                icon: 'none',
                duration: 2000
              })
            }
          })
        }
      });
    }, 1000);
  }
});