离屏渲染

¥Offscreen Rendering

概述

¥Overview

离屏渲染可让你在位图或共享 GPU 纹理中获取 BrowserWindow 的内容，因此它可以在任何地方渲染，例如在 3D 场景中的纹理上。Electron 中的离屏渲染使用与 Chrom 嵌入式框架项目类似的方法。

¥Offscreen rendering lets you obtain the content of a BrowserWindow in a bitmap or a shared GPU texture, so it can be rendered anywhere, for example, on texture in a 3D scene. The offscreen rendering in Electron uses a similar approach to that of the Chromium Embedded Framework project.

注意：

¥Notes:

有两种渲染模式可以使用（请参阅下面的部分），并且仅将脏区域传递给 paint 事件以提高效率。

¥There are two rendering modes that can be used (see the section below) and only the dirty area is passed to the paint event to be more efficient.
你可以停止/继续渲染以及设置帧速率。

¥You can stop/continue the rendering as well as set the frame rate.
最大帧速率为 240，因为更大的值只会带来性能损失，而没有任何好处。

¥The maximum frame rate is 240 because greater values bring only performance losses with no benefits.
当网页上没有发生任何事情时，不会生成任何框架。

¥When nothing is happening on a webpage, no frames are generated.
屏幕外窗口始终作为无框窗创建。

¥An offscreen window is always created as a Frameless Window.

渲染模式

¥Rendering Modes

GPU 加速

¥GPU accelerated

GPU 加速渲染是指使用 GPU 进行合成。这种模式的好处是支持 WebGL 和 3D CSS 动画。根据 webPreferences.offscreen.useSharedTexture 设置，有两种不同的方法。

¥GPU accelerated rendering means that the GPU is used for composition. The benefit of this mode is that WebGL and 3D CSS animations are supported. There are two different approaches depending on the webPreferences.offscreen.useSharedTexture setting.

使用 GPU 共享纹理

¥Use GPU shared texture

当 webPreferences.offscreen.useSharedTexture 设置为 true 时使用。

¥Used when webPreferences.offscreen.useSharedTexture is set to true.

这是一项高级功能，需要原生节点模块才能与你自己的代码一起使用。帧直接复制到 GPU 纹理中，因此这种模式非常快，因为没有 CPU-GPU 内存复制开销，并且你可以直接将共享纹理导入你自己的渲染程序。

¥This is an advanced feature requiring a native node module to work with your own code. The frames are directly copied in GPU textures, thus this mode is very fast because there's no CPU-GPU memory copies overhead, and you can directly import the shared texture to your own rendering program.
使用 CPU 共享内存位图

¥Use CPU shared memory bitmap

当 webPreferences.offscreen.useSharedTexture 设置为 false（默认行为）时使用。

¥Used when webPreferences.offscreen.useSharedTexture is set to false (default behavior).

可以使用 NativeImage API 访问纹理，但性能会受到影响。必须将帧从 GPU 复制到 CPU 位图，这需要更多的系统资源，因此此模式比软件输出设备模式慢。但它支持 GPU 相关功能。

¥The texture is accessible using the NativeImage API at the cost of performance. The frame has to be copied from the GPU to the CPU bitmap which requires more system resources, thus this mode is slower than the Software output device mode. But it supports GPU related functionalities.

软件输出设备

¥Software output device

此模式使用软件输出设备在 CPU 中进行渲染，因此帧生成比共享内存位图 GPU 加速模式更快。

¥This mode uses a software output device for rendering in the CPU, so the frame generation is faster than shared memory bitmap GPU accelerated mode.

要启用此模式，必须通过调用 app.disableHardwareAcceleration() API 禁用 GPU 加速。

¥To enable this mode, GPU acceleration has to be disabled by calling the app.disableHardwareAcceleration() API.

示例

¥Example

docs/fiddles/features/offscreen-rendering (34.0.0)Open in Fiddle

main.js

const { app, BrowserWindow } = require('electron/main')
const fs = require('node:fs')
const path = require('node:path')

app.disableHardwareAcceleration()

function createWindow () {
  const win = new BrowserWindow({
    width: 800,
    height: 600,
    webPreferences: {
      offscreen: true
    }
  })

  win.loadURL('https://github.com')
  win.webContents.on('paint', (event, dirty, image) => {
    fs.writeFileSync('ex.png', image.toPNG())
  })
  win.webContents.setFrameRate(60)
  console.log(`The screenshot has been successfully saved to ${path.join(process.cwd(), 'ex.png')}`)
}

app.whenReady().then(() => {
  createWindow()

  app.on('activate', () => {
    if (BrowserWindow.getAllWindows().length === 0) {
      createWindow()
    }
  })
})

app.on('window-all-closed', () => {
  if (process.platform !== 'darwin') {
    app.quit()
  }
})

启动 Electron 应用后，导航到应用的工作文件夹，你将在其中找到渲染的图片。

¥After launching the Electron application, navigate to your application's working folder, where you'll find the rendered image.

概述​

渲染模式​

GPU 加速​

软件输出设备​

示例​

概述

渲染模式

GPU 加速

软件输出设备

示例