从零开始用electron手撸一个截屏工具的示例代码

 { "name": "electorn-capture-screen", "version": "1.0.0", "main": "main.js", "repository": "https://github.com/chrisbing/electorn-capture-screen.git", "author": "Chris", "license": "MIT", "scripts": { "start": "electron ." }, "dependencies": { "electron": "^3.0.2" } }

 const { app, BrowserWindow, ipcMain, globalShortcut } = require('electron') const os = require('os') // Keep a global reference of the window object, if you don't, the window will // be closed automatically when the JavaScript object is garbage collected. let win function createWindow() { // 创建浏览器窗口。 win = new BrowserWindow({ width: 800, height: 600 }) // 然后加载应用的 index.html。 win.loadFile('index.html') // 打开开发者工具 win.webContents.openDevTools() // 当 window 被关闭，这个事件会被触发。 win.on('closed', () => { // 取消引用 window 对象，如果你的应用支持多窗口的话， // 通常会把多个 window 对象存放在一个数组里面， // 与此同时，你应该删除相应的元素。 win = null }) } // Electron 会在初始化后并准备 // 创建浏览器窗口时，调用这个函数。 // 部分 API 在 ready 事件触发后才能使用。 app.on('ready', createWindow) // 当全部窗口关闭时退出。 app.on('window-all-closed', () => { // 在 macOS 上，除非用户用 Cmd + Q 确定地退出， // 否则绝大部分应用及其菜单栏会保持激活。 if (process.platform !== 'darwin') { app.quit() } }) app.on('activate', () => { // 在macOS上，当单击dock图标并且没有其他窗口打开时， // 通常在应用程序中重新创建一个窗口。 if (win === null) { createWindow() } })

    Capture Screen

 // index.html const { ipcRenderer } = require('electron') document.getElementById('js-capture').addEventListener('click', ()=>{ ipcRenderer.send('capture-screen') })

 // main.js // 接收事件 ipcMain.on('capture-screen', captureScreen)

 // main.js // 注册全局快捷键 // globalShortcut 需要在 app ready 之后 globalShortcut.register('CmdOrCtrl+Shift+A', captureScreen) globalShortcut.register('Esc', () => { if (captureWin) { captureWin.close() captureWin = null } })

 // main.js let captureWin = null const captureScreen = (e, args) => { if (captureWin) { return } const { screen } = require('electron') let { width, height } = screen.getPrimaryDisplay().bounds captureWin = new BrowserWindow({ // window 使用 fullscreen, mac 设置为 undefined, 不可为 false fullscreen: os.platform() === 'win32' || undefined, // win width, height, x: 0, y: 0, transparent: true, frame: false, skipTaskbar: true, autoHideMenuBar: true, movable: false, resizable: false, enableLargerThanScreen: true, // mac hasShadow: false, }) captureWin.setAlwaysOnTop(true, 'screen-saver') // mac captureWin.setVisibleOnAllWorkspaces(true) // mac captureWin.setFullScreenable(false) // mac captureWin.loadFile(path.join(__dirname, 'capture.html')) // 调试用 // captureWin.openDevTools() captureWin.on('closed', () => { captureWin = null }) }

 // capture.html 
 

 @import "./assets/iconfont/iconfont.css"; html, body, div { margin: 0; padding: 0; box-sizing: border-box; } .mask { position: absolute; top: 0; left: 0; width: 100%; height: 100%; background: rgba(0, 0, 0, 0.6); } .bg { position: absolute; top: 0; left: 0; width: 100%; height: 100%; } .image-canvas { position: absolute; display: none; z-index: 1; } .size-info { position: absolute; color: #ffffff; font-size: 12px; background: rgba(40, 40, 40, 0.8); padding: 5px 10px; border-radius: 2px; font-family: Arial Consolas sans-serif; display: none; z-index: 2; } .toolbar { position: absolute; color: #343434; font-size: 12px; background: #f5f5f5; padding: 5px 10px; border-radius: 4px; font-family: Arial Consolas sans-serif; display: none; box-shadow: 0 0 20px rgba(0, 0, 0, 0.4); z-index: 2; align-items: center; } .toolbar .iconfont { font-size: 24px; padding: 2px 5px; }

 // capture-renderer.js const { ipcRenderer, clipboard, nativeImage, remote, desktopCapturer, screen } = require('electron') const Event = require('events') const fs = require('fs') const { bounds: { width, height }, scaleFactor } = screen.getPrimaryDisplay() const $canvas = document.getElementById('js-canvas') const $bg = document.getElementById('js-bg') const $sizeInfo = document.getElementById('js-size-info') const $toolbar = document.getElementById('js-toolbar') const $btnClose = document.getElementById('js-tool-close') const $btnOk = document.getElementById('js-tool-ok') const $btnSave = document.getElementById('js-tool-save') const $btnReset = document.getElementById('js-tool-reset') console.time('capture') desktopCapturer.getSources({ types: ['screen'], thumbnailSize: { width: width * scaleFactor, height: height * scaleFactor, } }, (error, sources) => { console.timeEnd('capture') let imgSrc = sources[0].thumbnail.toDataURL() let capture = new CaptureRenderer($canvas, $bg, imgSrc, scaleFactor) })

 // capture-renderer.js class CaptureRenderer extends Event { constructor($canvas, $bg, imageSrc, scaleFactor) { super() // ... this.init().then(() => { console.log('init') }) } async init() { this.$bg.style.backgroundImage = `url(${this.imageSrc})` this.$bg.style.backgroundSize = `${width}px ${height}px` let canvas = document.createElement('canvas') let ctx = canvas.getContext('2d') let img = await new Promise(resolve => { let img = new Image() img.src = this.imageSrc if (img.complete) { resolve(img) } else { img.onload = () => resolve(img) } }) canvas.width = img.width canvas.height = img.height ctx.drawImage(img, 0, 0) this.bgCtx = ctx // ... } // ... onMouseDrag(e) { // ... this.selectRect = {x, y, w, h, r, b} this.drawRect() this.emit('dragging', this.selectRect) // ... } drawRect() { if (!this.selectRect) { this.$canvas.style.display = 'none' return } const { x, y, w, h } = this.selectRect const scaleFactor = this.scaleFactor let margin = 7 let radius = 5 this.$canvas.style.left = `${x - margin}px` this.$canvas.style.top = `${y - margin}px` this.$canvas.style.width = `${w + margin * 2}px` this.$canvas.style.height = `${h + margin * 2}px` this.$canvas.style.display = 'block' this.$canvas.width = (w + margin * 2) * scaleFactor this.$canvas.height = (h + margin * 2) * scaleFactor if (w && h) { let imageData = this.bgCtx.getImageData(x * scaleFactor, y * scaleFactor, w * scaleFactor, h * scaleFactor) this.ctx.putImageData(imageData, margin * scaleFactor, margin * scaleFactor) } this.ctx.fillStyle = '#ffffff' this.ctx.strokeStyle = '#67bade' this.ctx.lineWidth = 2 * this.scaleFactor this.ctx.strokeRect(margin * scaleFactor, margin * scaleFactor, w * scaleFactor, h * scaleFactor) this.drawAnchors(w, h, margin, scaleFactor, radius) } drawAnchors(w, h, margin, scaleFactor, radius) { // ... } onMouseMove(e) { // ... document.body.style.cursor = 'move' // ... } onMouseUp(e) { this.emit('end-dragging') this.drawRect() } getImageUrl() { const { x, y, w, h } = this.selectRect if (w && h) { let imageData = this.bgCtx.getImageData(x * scaleFactor, y * scaleFactor, w * scaleFactor, h * scaleFactor) let canvas = document.createElement('canvas') let ctx = canvas.getContext('2d') ctx.putImageData(imageData, 0, 0) return canvas.toDataURL() } return '' } reset() { // ... } }

 // capture-renderer.js let onDrag = (selectRect) => { $toolbar.style.display = 'none' $sizeInfo.style.display = 'block' $sizeInfo.innerText = `${selectRect.w} * ${selectRect.h}` if (selectRect.y > 35) { $sizeInfo.style.top = `${selectRect.y - 30}px` } else { $sizeInfo.style.top = `${selectRect.y + 10}px` } $sizeInfo.style.left = `${selectRect.x}px` } capture.on('start-dragging', onDrag) capture.on('dragging', onDrag) let onDragEnd = () => { if (capture.selectRect) { const { x, r, b, y } = capture.selectRect $toolbar.style.display = 'flex' $toolbar.style.top = `${b + 15}px` $toolbar.style.right = `${window.screen.width - r}px` } } capture.on('end-dragging', onDragEnd) capture.on('reset', () => { $toolbar.style.display = 'none' $sizeInfo.style.display = 'none' })

 // capture-renderer.js const audio = new Audio() audio.src = './assets/audio/capture.mp3' let selectCapture = () => { if (!capture.selectRect) { return } let url = capture.getImageUrl() remote.getCurrentWindow().hide() audio.play() audio.onended = () => { window.close() } clipboard.writeImage(nativeImage.createFromDataURL(url)) ipcRenderer.send('capture-screen', { type: 'complete', url, }) } $btnOk.addEventListener('click', selectCapture)

 // capture-renderer.js $btnSave.addEventListener(‘click', () => { let url = capture.getImageUrl() remote.getCurrentWindow().hide() remote.dialog.showSaveDialog({ filters: [{ name: ‘Images', extensions: [‘png', ‘jpg', ‘gif'] }] }, function (path) { if (path) { fs.writeFile(path, new Buffer(url.replace(‘data:image/png;base64,', ‘'), ‘base64'), function () { ipcRenderer.send(‘capture-screen', { type: ‘complete', url, path, }) window.close() }) } else { ipcRenderer.send(‘capture-screen', { type: ‘cancel', url, }) window.close() } }) })

 ├── index.html ├── lib // 截图核心代码 │  ├── assets // font 和 声音资源 │  ├── capture-main.js // main 中截图部分代码 │  ├── capture-renderer.js // 截图交互代码 │  └── capture.html // 截图 html ├── main.js └── package.json