Rendu hors de l'écran

Vue d'ensemble

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. Le rendu hors écran d'Electron utilise une approche similaire à celle du projet Chromium Embedded Framework.

Notes :

• Il y a deux modes de rendu qui peuvent être utilisés (voir la section ci-dessous) et seule la zone modifiée est concernée par l'événement paint pour plus d'efficacité.
• Vous pouvez stopper/reprendre le rendu ainsi que définir la fréquence d'affichage de l’image.
• Le taux de rafraîchissement maximal est de 240 car des valeurs plus élevées n'apportent que des pertes de performances sans avantage particulier.
• Quand rien ne se passe sur une page Web, aucune image n'est générée.
• An offscreen window is always created as a Frameless Window.

Mode de rendu

Accélération GPU

Le rendu par l'acceleration GPU signifie que le GPU est utilisé pour la 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.

1. Use GPU shared texture

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

   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.

2. Use CPU shared memory bitmap

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

   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.

Périphérique d'affichage logiciel

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.

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

Exemple

docs/fiddles/features/offscreen-rendering (33.2.1)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()
  }
})

Après avoir lancé l'application Electron, accédez au dossier contenant votre application et vous y trouverez l'image du rendu.