canvas加入代码是啥

Posted 2023-03-22

参考技术A 1. 原生canvas实现用到的API

1） getContext(contextID) ---返回一个用于在画布上绘图的环境

复制代码代码如下:Canvas.getContext('2d') // 返回一个 CanvasRenderingContext2D 对象，使用它可以绘制到 Canvas 元素中

2）drawImage

drawImage(imgObj, x, y) // 按原图大小绘制, x、y为图片在画布中的位置坐标drawImage(imgObj, x, y, width, height) // 按指定宽高绘制drawImage(imgObj, sourceX, sourceY, sourceWidth, sourceHeight, destX, destY, destWidth, destHeight) // 从原来图片上某一个位置开始(sourceX,sourceY)，指定长宽进行剪切(sourceWidth,sourceHeight),然后将剪切的内容放到位置为(destX,destY),宽度为(destWidth),高度为(destHeight)的位置上
3） getImageData(x, y, width, height) ---获取矩形区域的图像信息

ctx.getImageData(0, 0, 10, 10) // 获取左上角坐标为(0, 0)，宽高为区域内的图像信息// 返回ImageData： width: 10, height: 10, data: Uint8ClampedArray[400]
4）beginPath() ---开始一条路径，或重置当前的路径 5）rect(x, y, width, height) ---绘制矩形

6）lineWidth ---设置或返回当前线条的宽度

7）fillStyle ---设置或返回用于填充绘画的颜色、渐变或模式

ctx.fillStyle = color|gradient|pattern
8）strokeStyle ---设置或返回用于笔触的颜色、渐变或模式

9）globalAlpha ---设置或返回绘图的当前透明值

10）fill() ---填充当前的图像（路径）。默认颜色是黑色

【注】如果路径未关闭，那么 fill() 方法会从路径结束点到开始点之间添加一条线，以关闭该路径，然后填充该路径。

11）stroke() ---会实际地绘制出通过 moveTo() 和 lineTo() 方法定义的路径。默认颜色是黑色

12）toDataURL(type, encoderOptions) ---导出图片，type为图片类型， encoderOptions图片质量，[0, 1]

Canvas.toDataURL("image/png", 1)
2. fabric.js

简化canvas编写的库，为canvas提供所缺少的对象模型

fabric.js能做的事

1）在canvas上创建、填充图形（包括图片、文字、规则图形和复杂路径组成图形）

2）给图形填充渐变颜色

3）组合图形（包括组合图形、图形文字、图片等）

4）设置图形动画集用户交互

5）生成JSON, SVG数据等

3.使用fabric.js实现用到的API

1）声明画布

let canvas =new fabric.Canvas('canvas') width: 200, height: 200
插入图片

let imgInstance = new fabric.Image(imgElement, left: 0, top: 0, width: 100, height: 100, angle: 0
3）设置背景图片 setBackgroundImage

canvas.setBackgroundImage(imgInstance)
4）renderAll() 重新绘制

5）on() 用户交互

canvas.on('mouse:down', function(options) console.log(options.e.clientX, options.e.clientY) )// 监听事件
6）getPointer()

7）setWidth()、setHeight() 设置canvas的宽高

8）画矩形

let rect = new fabric.Rect( left: 0, top: 0, width: 100, height: 100)
add(obj) 添加图形

canvas.add(rect)
10）remove(obj) 移除图形

11）set() 设置对象内容

12）toDataURL(obj)

4.原生canvas实现代码

<template><div class="container"> <div class="operations"> <ul> <li @click="mosaic">马赛克</li> <li @click="addText">添加文字</li> <li @click="tailor">裁剪</li> <li @click="rotate">旋转</li> <li @click="exportImg">导出图片</li> </ul> </div> <canvas ref="imgContent" class="img-wrap"> 你的浏览器太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() , // 打马赛克 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') , // 旋转 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) // 清理画布内容 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>