How do I configure viewport size and resolution in Headless Chromium?

To configure the viewport size and resolution in Headless Chromium, you generally use command-line flags when starting the browser, or you can set these parameters programmatically if you're using a browser automation library like Puppeteer for JavaScript or Selenium with ChromeDriver for Python.

Command-Line Flags

When you launch Headless Chromium from the command line, you can specify the window size using the --window-size flag:

chromium-browser --headless --disable-gpu --window-size=1920,1080 https://example.com

This command runs Chromium in headless mode, disables GPU hardware acceleration (which is often not necessary in headless mode), and sets the window size to 1920x1080 pixels.

Puppeteer (JavaScript)

When using Puppeteer, you can set the viewport size in your script. Here's an example:

const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch({
    headless: true,
    args: ['--disable-gpu'],
  });
  const page = await browser.newPage();
  await page.setViewport({
    width: 1920,
    height: 1080,
  });
  await page.goto('https://example.com');
  await page.screenshot({path: 'screenshot.png'});
  await browser.close();
})();

In this script, setViewport is used to set the size of the page as 1920x1080 pixels.

Selenium with ChromeDriver (Python)

For Python with Selenium, you would use the ChromeOptions class to specify the window size:

from selenium import webdriver

options = webdriver.ChromeOptions()
options.add_argument('--headless')
options.add_argument('--disable-gpu')
options.add_argument('window-size=1920x1080')

driver = webdriver.Chrome(options=options)
driver.get('https://example.com')

# Take a screenshot to verify the window size
driver.save_screenshot('screenshot.png')

driver.quit()

Here, the window-size argument is added to the ChromeOptions to set the desired window size before initializing the ChromeDriver.

Resolution

Setting the resolution in a headless browser typically refers to the window size, as shown above. If you are referring to the pixel density (like setting a HiDPI or Retina display), you can set the device scale factor using Puppeteer's setViewport method or a Chrome command-line flag.

For Puppeteer, it would look like this:

await page.setViewport({
  width: 1920,
  height: 1080,
  deviceScaleFactor: 2, // Sets the pixel density
});

For command-line flags, you would use the --force-device-scale-factor flag:

chromium-browser --headless --disable-gpu --window-size=1920,1080 --force-device-scale-factor=2 https://example.com

This flag sets the scaling factor for the display, which can simulate a high-resolution display.

Keep in mind that the actual availability of the flags and methods may vary depending on the version of the tools you are using. Always check the documentation for the most current options.