[web] Use fuzzy matching in Gold (flutter/engine#29847)

engine/src/flutter/lib/web_ui/dev/test_platform.dart

@@ -339,17 +339,20 @@ class BrowserPlatform extends PlatformPlugin {
         requestData['region'] as Map<String, dynamic>;
     final PixelComparison pixelComparison = PixelComparison.values.firstWhere(
         (PixelComparison value) => value.toString() == requestData['pixelComparison']);
+    final bool isCanvaskitTest = requestData['isCanvaskitTest'] as bool;
     final String result = await _diffScreenshot(
-        filename, write, maxDiffRate, region, pixelComparison);
+        filename, write, maxDiffRate, region, pixelComparison, isCanvaskitTest);
     return shelf.Response.ok(json.encode(result));
   }
 
   Future<String> _diffScreenshot(
-      String filename,
-      bool write,
-      double maxDiffRateFailure,
-      Map<String, dynamic> region,
-      PixelComparison pixelComparison) async {
+    String filename,
+    bool write,
+    double maxDiffRateFailure,
+    Map<String, dynamic> region,
+    PixelComparison pixelComparison,
+    bool isCanvaskitTest,
+  ) async {
     if (doUpdateScreenshotGoldens) {
       write = true;
     }
@@ -387,6 +390,7 @@ class BrowserPlatform extends PlatformPlugin {
       pixelComparison,
       maxDiffRateFailure,
       skiaClient,
+      isCanvaskitTest: isCanvaskitTest,
       goldensDirectory: goldensDirectory,
       filenameSuffix: _screenshotManager!.filenameSuffix,
       write: write,

engine/src/flutter/web_sdk/web_engine_tester/lib/golden_tester.dart

@@ -6,10 +6,9 @@ import 'dart:async';
 import 'dart:convert';
 import 'dart:html' as html;
 
-import 'package:ui/src/engine.dart';
-import 'package:ui/ui.dart';
-
 import 'package:test/test.dart';
+import 'package:ui/src/engine.dart' show operatingSystem, OperatingSystem, useCanvasKit;
+import 'package:ui/ui.dart';
 
 Future<dynamic> _callScreenshotServer(dynamic requestData) async {
   final html.HttpRequest request = await html.HttpRequest.request(
@@ -63,6 +62,7 @@ Future<void> matchGoldenFile(String filename,
             'height': region.height
           },
     'pixelComparison': pixelComparison.toString(),
+    'isCanvaskitTest': useCanvasKit,
   };
 
   // Chrome on macOS renders slightly differently from Linux, so allow it an

engine/src/flutter/web_sdk/web_test_utils/lib/image_compare.dart

@@ -32,6 +32,7 @@ Future<String> compareImage(
   PixelComparison pixelComparison,
   double maxDiffRateFailure,
   SkiaGoldClient? skiaClient, {
+  required bool isCanvaskitTest,
   // TODO(mdebbar): Remove these args with goldens repo.
   String goldensDirectory = '',
   String filenameSuffix = '',
@@ -43,7 +44,7 @@ Future<String> compareImage(
     // comparison.
 
     // TODO(mdebbar): Use Skia Gold for comparison, not only for uploading.
-    await _uploadToSkiaGold(skiaClient, screenshot, filename);
+    await _uploadToSkiaGold(skiaClient, screenshot, filename, isCanvaskitTest);
   }
 
   filename = filename.replaceAll('.png', '$filenameSuffix.png');
@@ -163,6 +164,7 @@ Future<void> _uploadToSkiaGold(
   SkiaGoldClient skiaClient,
   Image screenshot,
   String filename,
+  bool isCanvaskitTest,
 ) async {
   // Can't upload to Gold Skia unless running in LUCI.
   assert(_isLuci);
@@ -172,11 +174,13 @@ Future<void> _uploadToSkiaGold(
   final File goldenFile = File(p.join(environment.webUiSkiaGoldDirectory.path, filename));
   await goldenFile.writeAsBytes(encodePng(screenshot), flush: true);
 
+  final int screenshotSize = screenshot.width * screenshot.height;
+
   if (_isPreSubmit) {
-    return _uploadInPreSubmit(skiaClient, filename, goldenFile);
+    return _uploadInPreSubmit(skiaClient, filename, goldenFile, screenshotSize, isCanvaskitTest);
   }
   if (_isPostSubmit) {
-    return _uploadInPostSubmit(skiaClient, filename, goldenFile);
+    return _uploadInPostSubmit(skiaClient, filename, goldenFile, screenshotSize, isCanvaskitTest);
   }
 }
 
@@ -184,16 +188,20 @@ Future<void> _uploadInPreSubmit(
   SkiaGoldClient skiaClient,
   String filename,
   File goldenFile,
+  int screenshotSize,
+  bool isCanvaskitTest,
 ) {
   assert(_isPreSubmit);
-  return skiaClient.tryjobAdd(filename, goldenFile);
+  return skiaClient.tryjobAdd(filename, goldenFile, screenshotSize, isCanvaskitTest);
 }
 
 Future<void> _uploadInPostSubmit(
   SkiaGoldClient skiaClient,
   String filename,
   File goldenFile,
+  int screenshotSize,
+  bool isCanvaskitTest,
 ) {
   assert(_isPostSubmit);
-  return skiaClient.imgtestAdd(filename, goldenFile);
+  return skiaClient.imgtestAdd(filename, goldenFile, screenshotSize, isCanvaskitTest);
 }

engine/src/flutter/web_sdk/web_test_utils/lib/skia_client.dart

@@ -16,6 +16,13 @@ const String _kGoldctlKey = 'GOLDCTL';
 const String _skiaGoldHost = 'https://flutter-engine-gold.skia.org';
 const String _instance = 'flutter-engine';
 
+/// The percentage of accepted pixels to be wrong.
+///
+/// This should be a double between 0.0 and 1.0. A value of 0.0 means we don't
+/// accept any pixel to be different. A value of 1.0 means we accept 100% of
+/// pixels to be different.
+const double kMaxDifferentPixelsRate = 0.1;
+
 /// A client for uploading image tests and making baseline requests to the
 /// Flutter Gold Dashboard.
 class SkiaGoldClient {
@@ -162,7 +169,12 @@ class SkiaGoldClient {
   ///
   /// The [testName] and [goldenFile] parameters reference the current
   /// comparison being evaluated.
-  Future<bool> imgtestAdd(String testName, File goldenFile) async {
+  Future<bool> imgtestAdd(
+    String testName,
+    File goldenFile,
+    int screenshotSize,
+    bool isCanvaskitTest,
+  ) async {
     await _imgtestInit();
 
     final List<String> imgtestCommand = <String>[
@@ -171,6 +183,7 @@ class SkiaGoldClient {
       '--work-dir', _tempPath,
       '--test-name', cleanTestName(testName),
       '--png-file', goldenFile.path,
+      ..._getMatchingArguments(testName, screenshotSize, isCanvaskitTest),
     ];
 
     final ProcessResult result = await process.run(imgtestCommand);
@@ -250,7 +263,12 @@ class SkiaGoldClient {
   ///
   /// The [testName] and [goldenFile] parameters reference the current
   /// comparison being evaluated.
-  Future<void> tryjobAdd(String testName, File goldenFile) async {
+  Future<void> tryjobAdd(
+    String testName,
+    File goldenFile,
+    int screenshotSize,
+    bool isCanvaskitTest,
+  ) async {
     await _tryjobInit();
 
     final List<String> imgtestCommand = <String>[
@@ -259,6 +277,7 @@ class SkiaGoldClient {
       '--work-dir', _tempPath,
       '--test-name', cleanTestName(testName),
       '--png-file', goldenFile.path,
+      ..._getMatchingArguments(testName, screenshotSize, isCanvaskitTest),
     ];
 
     final ProcessResult result = await process.run(imgtestCommand);
@@ -279,6 +298,44 @@ class SkiaGoldClient {
     }
   }
 
+  List<String> _getMatchingArguments(
+    String testName,
+    int screenshotSize,
+    bool isCanvaskitTest,
+  ) {
+    // The algorithm to be used when matching images. The available options are:
+    // - "fuzzy": Allows for customizing the thresholds of pixel differences.
+    // - "sobel": Same as "fuzzy" but performs edge detection before performing
+    //            a fuzzy match.
+    const String algorithm = 'fuzzy';
+
+    // The number of pixels in this image that are allowed to differ from the
+    // baseline. It's okay for this to be a slightly high number like 10% of the
+    // image size because those wrong pixels are constrained by
+    // `pixelDeltaThreshold` below.
+    final int maxDifferentPixels = (screenshotSize * kMaxDifferentPixelsRate).toInt();
+
+    // The maximum acceptable difference in RGB channels of each pixel.
+    //
+    // ```
+    // abs(r(image) - r(golden)) + abs(g(image) - g(golden)) + abs(b(image) - b(golden)) <= pixelDeltaThreshold
+    // ```
+    final String pixelDeltaThreshold;
+    if (isCanvaskitTest) {
+      pixelDeltaThreshold = '21';
+    } else if (browserName == 'ios-safari') {
+      pixelDeltaThreshold = '15';
+    } else {
+      pixelDeltaThreshold = '3';
+    }
+
+    return <String>[
+      '--add-test-optional-key', 'image_matching_algorithm:$algorithm',
+      '--add-test-optional-key', 'fuzzy_max_different_pixels:$maxDifferentPixels',
+      '--add-test-optional-key', 'fuzzy_pixel_delta_threshold:$pixelDeltaThreshold',
+    ];
+  }
+
   /// Returns the latest positive digest for the given test known to Skia Gold
   /// at head.
   Future<String?> getExpectationForTest(String testName) async {
@@ -356,9 +413,9 @@ class SkiaGoldClient {
   /// browser the image was rendered on.
   Map<String, dynamic> _getKeys() {
     return <String, dynamic>{
+      'Browser': browserName,
       'CI': 'luci',
       'Platform': Platform.operatingSystem,
-      'Browser': browserName,
     };
   }