小程序生成海报 canvas

前言

微信小程序需要生成海报进行朋友圈分享，但是不同的手机会有问题，

然后首先是图片的问题

图片

在模拟器上没有报错，可是真机测试却什么也没画出来。 canvas.drawImage 是不支持网络图片的，只支持本地图片。

所以，任何的网络图片都需要先缓存到本地，（当然上线的时候需要把网络图片的前缀加入白名单里面）

再通过 drawImage 调用存储的本地资源进行绘制，

缓存可以通过 wx.getImageInfo 和 wx.downloadFile 实现

wx.getImageInfo({
  src: 'https://i415454.jpg',
  success: function (res) {
    console.log(res.width)
    console.log(res.path)
  }
})

然后通过 draw 方法 的是 draw 方法是异步的，如果图片还没加载成功，有可能画出来的是空的，所以 draw 方法通常都会带有定时器这样的回调。

 this.ctx.draw(false, () => {
        wx.setStorageSync('canvasdrawer_pic_cache', this.cache)
        const system = wx.getSystemInfoSync().system
        if (/ios/i.test(system)) {
          this.saveImageToLocal()
        } else {
          // 延迟保存图片，解决安卓生成图片错位bug。
          setTimeout(() => {
            this.saveImageToLocal()
          }, 800)
        }
      })

画布首先分为 矩形， 图片，文字，线这几种，

是结合了promise 来处理 ，

产生的图片 直接通过 previewImage 进入手机预览模式，预览模式的图片可以直接保存到本地

然后就是我的DEMO 先放2张图

 这就是生成后的图片了

 先写组件  canvasdrawer

 js:

Component({
  properties: {
    painting: {
      type: Object,
      value: { view: [] },
      observer(newVal, oldVal) {
        if (!this.data.isPainting) {
          if (JSON.stringify(newVal) !== JSON.stringify(oldVal)) {
            if (newVal && newVal.width && newVal.height) {
              this.setData({
                showCanvas: true,
                isPainting: true
              })
              this.readyPigment()
            }
          } else {
            if (newVal && newVal.mode !== 'same') {
              this.triggerEvent('getImage', { errMsg: 'canvasdrawer:samme params' })
            }
          }
        }
      }
    }
  },
  data: {
    showCanvas: false,

     100,
    height: 100,

    tempFileList: [],

    isPainting: false
  },
  ctx: null,
  cache: {},
  ready() {
    wx.removeStorageSync('canvasdrawer_pic_cache')
    this.cache = wx.getStorageSync('canvasdrawer_pic_cache') || {}
    this.ctx = wx.createCanvasContext('canvasdrawer', this)
  },
  methods: {
    readyPigment() {
      const { width, height, views } = this.data.painting
      this.setData({
        width,
        height
      })

      const inter = setInterval(() => {
        if (this.ctx) {
          clearInterval(inter)
          this.ctx.clearActions()
          this.ctx.save()
          this.getImagesInfo(views)
        }
      }, 100)
    },
    getImagesInfo(views) {
      const imageList = []
      for (let i = 0; i < views.length; i++) {
        if (views[i].type === 'image') {
          imageList.push(this.getImageInfo(views[i].url))
        }
      }

      const loadTask = []
      for (let i = 0; i < Math.ceil(imageList.length / 8); i++) {
        loadTask.push(new Promise((resolve, reject) => {
          Promise.all(imageList.splice(i * 8, 8)).then(res => {
            resolve(res)
          }).catch(res => {
            reject(res)
          })
        }))
      }
      Promise.all(loadTask).then(res => {
        let tempFileList = []
        for (let i = 0; i < res.length; i++) {
          tempFileList = tempFileList.concat(res[i])
        }
        this.setData({
          tempFileList
        })
        this.startPainting()
      })
    },
    startPainting() {
      const { tempFileList, painting: { views } } = this.data
      for (let i = 0, imageIndex = 0; i < views.length; i++) {
        if (views[i].type === 'image') {
          this.drawImage({
            ...views[i],
            url: tempFileList[imageIndex]
          })
          imageIndex++
        } else if (views[i].type === 'text') {
          if (!this.ctx.measureText) {
            wx.showModal({
              title: '提示',
              content: '当前微信版本过低，无法使用 measureText 功能，请升级到最新微信版本后重试。'
            })
            this.triggerEvent('getImage', { errMsg: 'canvasdrawer:version too low' })
            return
          } else {
            this.drawText(views[i])
          }
        } else if (views[i].type === 'rect') {
          this.drawRect(views[i])
        }
      }
      this.ctx.draw(false, () => {
        wx.setStorageSync('canvasdrawer_pic_cache', this.cache)
        const system = wx.getSystemInfoSync().system
        if (/ios/i.test(system)) {
          this.saveImageToLocal()
        } else {
          // 延迟保存图片，解决安卓生成图片错位bug。
          setTimeout(() => {
            this.saveImageToLocal()
          }, 800)
        }
      })
    },
    drawImage(params) {
      this.ctx.save()
      const { url, top = 0, left = 0, width = 0, height = 0, borderRadius = 0, deg = 0 } = params
      if (borderRadius) {
        // 圓角
        this.ctx.beginPath()
        this.ctx.arc(width / 2 + left, height / 2 + top, width / 2, 0, Math.PI * 2, false);
        this.ctx.clip()
        this.ctx.drawImage(url, left, top, width, height)
      }  
     else if (deg !== 0) {
        this.ctx.translate(left + width / 2, top + height / 2)
        this.ctx.rotate(deg * Math.PI / 180)
        this.ctx.drawImage(url, -width / 2, -height / 2, width, height)
      } else {
        this.ctx.drawImage(url, left, top, width, height)
      }
      // }
      this.ctx.restore()
    },
    drawText(params) {
      this.ctx.save()
      const {
        MaxLineNumber = 2,
        breakWord = false,
        color = 'black',
        content = '',
        fontSize = 16,
        top = 0,
        left = 0,
        lineHeight = 20,
        textAlign = 'left',
        width,
        bolder = false,
        textDecoration = 'none'
      } = params

      this.ctx.beginPath()
      this.ctx.setTextBaseline('top')
      this.ctx.setTextAlign(textAlign)
      this.ctx.setFillStyle(color)
      this.ctx.setFontSize(fontSize)

      if (!breakWord) {
        this.ctx.fillText(content, left, top)
        this.drawTextLine(left, top, textDecoration, color, fontSize, content)
      } else {
        let fillText = ''
        let fillTop = top
        let lineNum = 1
        for (let i = 0; i < content.length; i++) {
          fillText += [content[i]]
          if (this.ctx.measureText(fillText).width > width) {
            if (lineNum === MaxLineNumber) {
              if (i !== content.length) {
                fillText = fillText.substring(0, fillText.length - 1) + '...'
                this.ctx.fillText(fillText, left, fillTop)
                this.drawTextLine(left, fillTop, textDecoration, color, fontSize, fillText)
                fillText = ''
                break
              }
            }
            this.ctx.fillText(fillText, left, fillTop)
            this.drawTextLine(left, fillTop, textDecoration, color, fontSize, fillText)
            fillText = ''
            fillTop += lineHeight
            lineNum++
          }
        }
        this.ctx.fillText(fillText, left, fillTop)
        this.drawTextLine(left, fillTop, textDecoration, color, fontSize, fillText)
      }

      this.ctx.restore()

      if (bolder) {
        this.drawText({
          ...params,
          left: left + 0.3,
          top: top + 0.3,
          bolder: false,
          textDecoration: 'none'
        })
      }
    },
    drawTextLine(left, top, textDecoration, color, fontSize, content) {
      if (textDecoration === 'underline') {
        this.drawRect({
          background: color,
          top: top + fontSize * 1.2,
          left: left - 1,
           this.ctx.measureText(content).width + 3,
          height: 1
        })
      } else if (textDecoration === 'line-through') {
        this.drawRect({
          background: color,
          top: top + fontSize * 0.6,
          left: left - 1,
           this.ctx.measureText(content).width + 3,
          height: 1
        })
      }
    },
    drawRect(params) {
      this.ctx.save()
      const { background, top = 0, left = 0, width = 0, height = 0, radius = 0 } = params
      this.ctx.setFillStyle(background)
      this.ctx.fillRect(left, top, width, height)
      
      if (radius!=0){
        this.ctx.beginPath()
        this.ctx.setFillStyle(background)
        this.ctx.setStrokeStyle(background);
        this.ctx.setLineJoin('round');  //交点设置成圆角
        this.ctx.setLineWidth(radius) ;
        this.ctx.strokeRect(width + radius / 2, height + radius / 2, width - radius, height - radius);
        this.ctx.fillRect(width + radius, height + radius, width - radius * 2, height - radius * 2);
        this.ctx.stroke();
        this.ctx.closePath();
      }
      this.ctx.restore();
    },
    getImageInfo(url) {
      return new Promise((resolve, reject) => {
        if (this.cache[url]) {
          resolve(this.cache[url])
        } else {
          const objExp = new RegExp(/^http(s)?://([w-]+.)+[w-]+(/[w- ./?%&=]*)?/)
          if (objExp.test(url)) {
            wx.getImageInfo({
              src: url,
              complete: res => {
                if (res.errMsg === 'getImageInfo:ok') {
                  this.cache[url] = res.path
                  resolve(res.path)
                } else {
                  this.triggerEvent('getImage', { errMsg: 'canvasdrawer:download fail' })
                  reject(new Error('getImageInfo fail'))
                }
              }
            })
          } else {
            this.cache[url] = url
            resolve(url)
          }
        }
      })
    },
    saveImageToLocal() {
      const { width, height } = this.data
      wx.canvasToTempFilePath({
        x: 0,
        y: 0,
        width,
        height,
        canvasId: 'canvasdrawer',
        complete: res => {
          if (res.errMsg === 'canvasToTempFilePath:ok') {
            this.setData({
              showCanvas: false,
              isPainting: false,
              tempFileList: []
            })
            this.triggerEvent('getImage', { tempFilePath: res.tempFilePath, errMsg: 'canvasdrawer:ok' })
          } else {
            this.triggerEvent('getImage', { errMsg: 'canvasdrawer:fail' })
          }
        }
      }, this)
    }
  }
})

html :

<canvas canvas-id="canvasdrawer" style="{{width}}px;height:{{height}}px;" class="board" wx:if="{{showCanvas}}"></canvas>

css:

.board {
  position: fixed;
  top: 2000rpx;
}

在页面中调用这个组件 canvasdrawer

html:

<canvasdrawer painting="{{painting}}" class="canvasdrawer" bind:getImage="eventGetImage"/>

js:

 // 生成
    eventDraw() {
      wx.showLoading({
        title: '绘制分享图片中',
        mask: true
      })
      this.setData({
        painting: {
           375,
          height: app.globalData.screenHeight,
          clear: true,
          views: [
            {
              type: 'rect',
              background: this.data.skin.theme_color,
              top: 0,
              left: 0,
               375,
              radius:10,
              height: app.globalData.screenHeight,
            },
            {
              type: 'image',
              url: '/images/common/posterBg.png',  // 背景 //https://hybrid.xiaoying.tv/miniprogram/viva-ad/1/1531103986231.jpeg
              top: 0,
              left: 0,
               375,
              height: 667
            },
            {
              type: 'image',
              url: '/images/common/avatar.png', 
              top: 274,
              left: 30,
               45,
              borderRadius:45,
              height: 45  //头像
            },
            {
              type: 'text',
              content: '大帅比哈哈',
              fontSize: 15,
              color: '#333333',
              textAlign: 'left',
              top: 564/2,
              left: 162/2,
              bolder: false
            },
            {
              type: 'text',
              content: '邀请你一起来享受优惠！',
              fontSize: 13,
              color: this.data.skin.theme_color,
              textAlign: 'left',
              top: 611/2,
              left: 162 / 2
            },
            {
              type: 'image',
              url: this.data.shareActivity.topImage, //活动图片
              top: 104,
              left: 30,
                315,
              height: 159
            },
            {
              type: 'image',
              url: '/images/common/avatar.png',
              top: (600 +179) /2,
              left: 60,
               245/2,
              height: 245/2
            },
            {
              type: 'image',
              url: this.data.fingerImage, // 指紋 'https://hybrid.xiaoying.tv/miniprogram/viva-ad/1/1531385433625.jpeg'
              top: (615 + 179) / 2,
              left: 213,
               215 / 2,
              height: 215 / 2,        
            },
            {
              type: 'text',
              content: this.data.shareActivity.shareTitle, //'正品MAC魅可口红礼盒生日唇膏小辣椒Chili西柚情人',
              fontSize: 16,
              lineHeight: 21,
              color: '#383549',
              textAlign: 'left',
              top: 336,
              left: 30,
               310,
              MaxLineNumber: 2,
              breakWord: true,
              bolder: true
            },
            {
              type: 'text',
              content: '长按图片识别二维码，立即参与活动~',
              fontSize: 13,
              color: '#999',
              textAlign: 'left',
              top: (879+176)/ 2 ,
              left: 75,
              lineHeight: 20,
              MaxLineNumber: 2,
              breakWord: true,
               209
            }
          ]
        }
      })
    },


    //保存
    eventGetImage(event) {
      let _this = this;
      wx.hideLoading()
      const { tempFilePath, errMsg } = event.detail
      if (errMsg === 'canvasdrawer:ok') {
        this.setData({
          shareImage: tempFilePath,
        })

        wx.previewImage({
          urls: [tempFilePath],
          success: function () {
            _this.setData({
              isShareBtnDisabled: false,
              painting:{},
            })
          },
          fail: function () {
          }
        })
        
      }
    }

这要就可以啦  海报就兼容 苹果和安卓 手机 嘻嘻 

还需努力