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Minimal screenshot tool. #4074
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Minimal screenshot tool. #4074
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Original file line number | Diff line number | Diff line change |
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// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file | ||
// for details. All rights reserved. Use of this source code is governed by a | ||
// BSD-style license that can be found in the LICENSE file. | ||
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import 'dart:io'; | ||
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import 'package:path/path.dart' as p; | ||
import 'package:puppeteer/puppeteer.dart'; | ||
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// Default screen with 16:10 ratio. | ||
final desktopDeviceViewport = DeviceViewport(width: 1280, height: 800); | ||
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final _screenshotDir = Platform.environment['SCREENSHOT_DIR']; | ||
final isScreenshotDirSet = _screenshotDir != null && _screenshotDir!.isNotEmpty; | ||
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// Set this variable to enable screenshot files to be updated with new takes. | ||
// The default is to throw an exception to prevent accidental overrides from | ||
// separate tests. | ||
final _allowScreeshotUpdates = Platform.environment['SCREENSHOT_UPDATE'] == '1'; | ||
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// Note: The default values are the last, so we don't need reset | ||
// the original values after taking the screenshots. | ||
final _themes = ['dark', 'light']; | ||
final _viewports = { | ||
'mobile': DeviceViewport(width: 400, height: 800), | ||
'tablet': DeviceViewport(width: 768, height: 1024), | ||
'desktop': desktopDeviceViewport, | ||
}; | ||
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extension ScreenshotPageExt on Page { | ||
Future<void> writeScreenshotToFile(String path) async { | ||
await File(path).writeAsBytes(await screenshot()); | ||
} | ||
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/// Takes screenshots **if** `SCREENSHOT_DIR` environment variable is set. | ||
/// | ||
/// Iterates over viewports and themes, and generates screenshot files with the | ||
/// following pattern: | ||
/// - `SCREENSHOT_DIR/$prefix-desktop-dark.png` | ||
/// - `SCREENSHOT_DIR/$prefix-desktop-light.png` | ||
/// - `SCREENSHOT_DIR/$prefix-mobile-dark.png` | ||
/// - `SCREENSHOT_DIR/$prefix-mobile-light.png` | ||
/// - `SCREENSHOT_DIR/$prefix-tablet-dark.png` | ||
/// - `SCREENSHOT_DIR/$prefix-tablet-light.png` | ||
Future<void> takeScreenshots({ | ||
required String selector, | ||
required String prefix, | ||
}) async { | ||
final handle = await $(selector); | ||
await handle.takeScreenshots(prefix); | ||
} | ||
} | ||
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extension ScreenshotElementHandleExt on ElementHandle { | ||
/// Takes screenshots **if** `SCREENSHOT_DIR` environment variable is set. | ||
/// | ||
/// Iterates over viewports and themes, and generates screenshot files with the | ||
/// following pattern: | ||
/// - `SCREENSHOT_DIR/$prefix-desktop-dark.png` | ||
/// - `SCREENSHOT_DIR/$prefix-desktop-light.png` | ||
/// - `SCREENSHOT_DIR/$prefix-mobile-dark.png` | ||
/// - `SCREENSHOT_DIR/$prefix-mobile-light.png` | ||
/// - `SCREENSHOT_DIR/$prefix-tablet-dark.png` | ||
/// - `SCREENSHOT_DIR/$prefix-tablet-light.png` | ||
Future<void> takeScreenshots(String prefix) async { | ||
final body = await page.$('body'); | ||
final bodyClassAttr = (await body | ||
.evaluate<String>('el => el.getAttribute("class")')) as String; | ||
final bodyClasses = [ | ||
...bodyClassAttr.split(' '), | ||
'--ongoing-screenshot', | ||
]; | ||
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for (final vp in _viewports.entries) { | ||
await page.setViewport(vp.value); | ||
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for (final theme in _themes) { | ||
final newClasses = [ | ||
...bodyClasses.where((c) => !c.endsWith('-theme')), | ||
'$theme-theme', | ||
]; | ||
await body.evaluate<String>('(el, v) => el.setAttribute("class", v)', | ||
args: [newClasses.join(' ')]); | ||
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// The presence of the element is verified, continue only if screenshots are enabled. | ||
if (!isScreenshotDirSet) continue; | ||
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// Arbitrary delay in the hope that potential ongoing updates complete. | ||
await Future<void>.delayed(Duration(milliseconds: 500)); | ||
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final path = p.join(_screenshotDir!, '$prefix-${vp.key}-$theme.png'); | ||
await _writeScreenshotToFile(path); | ||
} | ||
} | ||
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// restore the original body class attributes | ||
await body.evaluate<String>('(el, v) => el.setAttribute("class", v)', | ||
args: [bodyClassAttr]); | ||
} | ||
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Future<void> _writeScreenshotToFile(String path) async { | ||
final file = File(path); | ||
final exists = file.existsSync(); | ||
if (exists && !_allowScreeshotUpdates) { | ||
throw Exception('Screenshot update is detected in: $path'); | ||
} | ||
await file.parent.create(recursive: true); | ||
await File(path).writeAsBytes(await screenshot()); | ||
} | ||
} |
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We might need to discuss if we want a non-dart-team dependency here (even if it is a dev-dependency)
cc @szakarias wdyt?
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I was thinking to implement this as an external screenshotting tool, mostly because there is no natural integration point with browser-based tests like in
pub-dev
's integration tests, and maybepub-dev
could reuse the tool as a library. wdyt?