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canvas實現圖片馬賽克的示例代碼

1. 原生canvas實現用到的API

1） getContext(contextID) ---返回一個用于在畫布上繪圖的環境

復制代碼

代碼如下:

Canvas.getContext('2d') // 返回一個 CanvasRenderingContext2D 對象，使用它可以繪制到 Canvas 元素中

2）drawImage

drawImage(imgObj, x, y)  // 按原圖大小繪制, x、y為圖片在畫布中的位置坐標
drawImage(imgObj, x, y, width, height) // 按指定寬高繪制
drawImage(imgObj, sourceX, sourceY, sourceWidth, sourceHeight, destX, destY, destWidth, destHeight) // 從原來圖片上某一個位置開始(sourceX,sourceY)，指定長寬進行剪切(sourceWidth,sourceHeight),然后將剪切的內容放到位置為(destX,destY),寬度為(destWidth),高度為(destHeight)的位置上

3） getImageData(x, y, width, height) ---獲取矩形區域的圖像信息

ctx.getImageData(0, 0, 10, 10) // 獲取左上角坐標為(0, 0)，寬高為區域內的圖像信息
// 返回ImageData： { width: 10, height: 10, data: Uint8ClampedArray[400] }

4）beginPath() ---開始一條路徑，或重置當前的路徑 5）rect(x, y, width, height) ---繪制矩形

6）lineWidth ---設置或返回當前線條的寬度

7）fillStyle ---設置或返回用于填充繪畫的顏色、漸變或模式

ctx.fillStyle = color|gradient|pattern

8）strokeStyle ---設置或返回用于筆觸的顏色、漸變或模式

9）globalAlpha ---設置或返回繪圖的當前透明值

10）fill() ---填充當前的圖像（路徑）。默認顏色是黑色

【注】如果路徑未關閉，那么 fill() 方法會從路徑結束點到開始點之間添加一條線，以關閉該路徑，然后填充該路徑。

11）stroke() ---會實際地繪制出通過 moveTo() 和 lineTo() 方法定義的路徑。默認顏色是黑色

12）toDataURL(type, encoderOptions) ---導出圖片，type為圖片類型， encoderOptions圖片質量，[0, 1]

Canvas.toDataURL("image/png", 1)

2. fabric.js

簡化canvas編寫的庫，為canvas提供所缺少的對象模型

fabric.js能做的事

1）在canvas上創建、填充圖形（包括圖片、文字、規則圖形和復雜路徑組成圖形）

2）給圖形填充漸變顏色

3）組合圖形（包括組合圖形、圖形文字、圖片等）

4）設置圖形動畫集用戶交互

5）生成JSON, SVG數據等

3.使用fabric.js實現用到的API

1）聲明畫布

let canvas =new fabric.Canvas('canvas') {
   width: 200,
   height: 200
}

插入圖片

let imgInstance = new fabric.Image(imgElement,{
  left: 0,
  top: 0,
  width: 100,
  height: 100,
  angle: 0
}

3）設置背景圖片 setBackgroundImage

canvas.setBackgroundImage(imgInstance)

4）renderAll() 重新繪制

5）on() 用戶交互

canvas.on('mouse:down', function(options) {  
   console.log(options.e.clientX, options.e.clientY)  
})

// 監聽事件
/* 
   mouse:down :鼠標按下時
   mouse:move :鼠標移動時
   mouse:up :鼠標抬起時
   after:render :畫布重繪后
   object:selected:對象被選中
   object:moving:對象移動
   object:rotating:對象被旋轉
   object:added:對象被加入
   object:removed對象被移除 
*/

6）getPointer()

7）setWidth()、setHeight() 設置canvas的寬高

8）畫矩形

let rect = new fabric.Rect({
 left: 0,
 top: 0,
 width: 100,
 height: 100
})

add(obj) 添加圖形

canvas.add(rect)

10）remove(obj) 移除圖形

11）set() 設置對象內容

12）toDataURL(obj)

4.原生canvas實現代碼

<template>
<div class="container">
  <div class="operations">
    <ul>
      <li @click="mosaic">馬賽克</li>
      <li @click="addText">添加文字</li>
      <li @click="tailor">裁剪</li>
      <li @click="rotate">旋轉</li>
      <li @click="exportImg">導出圖片</li>
    </ul>
  </div>
  <canvas ref="imgContent" class="img-wrap">
    你的瀏覽器太low🌶
  </canvas>
</div>
</template>

<script>
  export default {
    data () {
      return {
        context: '',
        canvas: '',
        isMasic: false,
        isText: false,
        isTailor: false,
        isTranslate: false,
        squareEdgeLength: 20,
        angle: 0,
        img: ''
      }
    },
    mounted () {
      this.initData()
    },
    methods: {
      initData () {
        let imgContent = this.$refs.imgContent
        this.canvas = imgContent
        this.context = imgContent.getContext('2d')
        let  Img = new Image()
        this.image = Img
        Img.crossOrigin = "Anonymous"
        Img.src = 'http://oia85104s.bkt.clouddn.com/PictureUnlock_193139.pictureunlock.jpg'
        this.canvas.setAttribute('width', Img.width)
        this.canvas.setAttribute('height', Img.height)
        let self = this
        Img.onload = () => {
          let beginX, beginY, endX, endY
          self.context.drawImage(Img, 0, 0)
          self.context.save()

          self.canvas.addEventListener('mousedown', e => {
            beginX = e.offsetX
            beginY = e.offsetY
            self.canvas.addEventListener('mouseup', e => {
              endX = e.offsetX
              endY = e.offsetY
              if (self.isMasic) {
                self.makeGrid(beginX, beginY, endX - beginX, endY - beginY)
                return
              }
              if (self.isTailor) {
                self.context.drawImage(Img, beginX, beginY, endX - beginX, endY - beginY, 0, 0, endX - beginX, endY - beginY)
                return
              }
            })
          })
        }
      },
      drawRect  (x, y, width, height, fillStyle, lineWidth, strokeStyle, globalAlpha) {
        this.context.beginPath()
        this.context.rect(x, y, width, height)
        this.context.lineWidth = lineWidth
        this.context.strokeStyle = strokeStyle
        fillStyle && (this.context.fillStyle = fillStyle)
        globalAlpha && (this.context.globalAlpha = globalAlpha)

        this.context.fill()
        this.context.stroke()
      },
      // 打馬賽克
      mosaic () {
        let self = this
        this.resetClickStatus()
        this.isMasic = true
      },
      makeGrid (beginX, beginY, rectWidth, rectHight) {
        const row = Math.round(rectWidth / this.squareEdgeLength) + 1
        const column = Math.round(rectHight / this.squareEdgeLength) + 1
        for (let i = 0; i < row * column; i++) {
          let x = (i % row) * this.squareEdgeLength + beginX
          let y = parseInt(i / row) * this.squareEdgeLength + beginY
          this.setColor(x, y)
        }
      },
      setColor (x, y) {
        const imgData = this.context.getImageData(x, y, this.squareEdgeLength, this.squareEdgeLength).data
        let r = 0, g = 0, b = 0
        console.log(this.context.getImageData(x, y, this.squareEdgeLength, this.squareEdgeLength), JSON.stringify(imgData))
        for (let i = 0; i < imgData.length; i += 4) {
          r += imgData[i]
          g += imgData[i + 1]
          b += imgData[i + 2]
        }
        r = Math.round(r / (imgData.length / 4))
        g = Math.round(g / (imgData.length / 4))
        b = Math.round(b / (imgData.length / 4))
        this.drawRect(x, y, this.squareEdgeLength, this.squareEdgeLength, `rgb(${r}, ${g}, ${b})`, 2, `rgb(${r}, ${g}, ${b})`)
      },
      // 添加文字
      addText () {
        this.resetClickStatus()
        this.isText = true
        console.log('添加文字')
      },
      // 裁剪
      tailor () {
        this.resetClickStatus()
        this.isTailor = true
        console.log('裁剪')
      } ,
      // 旋轉
      rotate () {
        // if (this.angle === 360) {
        //   this.angle = 90
        // } else {
        //   this.angle += 90
        // }
        // if ([90, 270].includes(this.angle)) {
        //   this.canvas.setAttribute('width', this.image.height)
        //   this.canvas.setAttribute('height', this.image.width)
        // } else {
        //   this.canvas.setAttribute('width', this.image.width)
        //   this.canvas.setAttribute('height', this.image.height)
        // }
        const x = this.image.width / 2
        const y = this.image.height / 2
        this.context.clearRect(0,0, this.canvas.width, this.canvas.height)  // 清理畫布內容
        this.context.translate(x, y)
        this.context.rotate(90 * Math.PI / 180)
        this.context.translate(-x, -y)
        this.context.drawImage(this.image, 0, 0)
      },
      resetClickStatus () {
        this.isMasic = false
        this.isText = false
        this.isTailor = false
        this.isTranslate = false
      },
      exportImg () {
        this.resetClickStatus()
        const exportUrl = this.canvas.toDataURL("image/jpeg")
        let a = document.createElement('a')
        a.setAttribute('download', '')
        a.href = exportUrl
        document.body.appendChild(a)
        a.click()
      }
    }
  }
</script>

<style scoped lang="less">
.operations {
  width: 1200px;
  margin: 0 auto;
  ul {
    display: flex;
    align-items: center;
    margin-bottom: 30px;
    li {
      list-style: none;
      margin-right: 20px;
      cursor: pointer;
    }
  }
}
.img-wrap {
  display: block;
  margin: 0 auto;
}
</style>

效果圖如下：