[Impeller] Adds the ability to specify a golden threshold (flutter/engine#40824)

[Impeller] Adds the ability to specify a golden threshold

engine/src/flutter/impeller/aiks/aiks_unittests.cc

@@ -1243,9 +1243,6 @@ TEST_P(AiksTest, CanRenderTextOutsideBoundaries) {
 }
 
 TEST_P(AiksTest, TextRotated) {
-#ifdef IMPELLER_GOLDEN_TESTS
-  GTEST_SKIP() << "Test has small differences on different mac hosts";
-#endif
   Canvas canvas;
   canvas.Transform(Matrix(0.5, -0.3, 0, -0.002,  //
                           0, 1, 0, 0,            //

engine/src/flutter/impeller/golden_tests/golden_digest.cc

@@ -6,6 +6,9 @@
 
 #include <fstream>
 
+static const double kMaxDiffPixelsPercent = 0.01;
+static const int32_t kMaxColorDelta = 8;
+
 namespace impeller {
 namespace testing {
 
@@ -24,7 +27,8 @@ void GoldenDigest::AddImage(const std::string& test_name,
                             const std::string& filename,
                             int32_t width,
                             int32_t height) {
-  entries_.push_back({test_name, filename, width, height});
+  entries_.push_back({test_name, filename, width, height, kMaxDiffPixelsPercent,
+                      kMaxColorDelta});
 }
 
 bool GoldenDigest::Write(WorkingDirectory* working_directory) {
@@ -46,8 +50,19 @@ bool GoldenDigest::Write(WorkingDirectory* working_directory) {
          << "\"testName\" : \"" << entry.test_name << "\", "
          << "\"filename\" : \"" << entry.filename << "\", "
          << "\"width\" : " << entry.width << ", "
-         << "\"height\" : " << entry.height << " "
-         << "}";
+         << "\"height\" : " << entry.height << ", ";
+
+    if (entry.max_diff_pixels_percent ==
+        static_cast<int64_t>(entry.max_diff_pixels_percent)) {
+      fout << "\"maxDiffPixelsPercent\" : " << entry.max_diff_pixels_percent
+           << ".0, ";
+    } else {
+      fout << "\"maxDiffPixelsPercent\" : " << entry.max_diff_pixels_percent
+           << ", ";
+    }
+
+    fout << "\"maxColorDelta\":" << entry.max_color_delta << " ";
+    fout << "}";
   }
   fout << std::endl << "]" << std::endl;
 

engine/src/flutter/impeller/golden_tests/golden_digest.h

@@ -36,6 +36,8 @@ class GoldenDigest {
     std::string filename;
     int32_t width;
     int32_t height;
+    double max_diff_pixels_percent;
+    int32_t max_color_delta;
   };
 
   static GoldenDigest* instance_;

engine/src/flutter/impeller/golden_tests/golden_playground_test_mac.cc

@@ -42,10 +42,9 @@ bool SaveScreenshot(std::unique_ptr<testing::MetalScreenshot> screenshot) {
 }  // namespace
 
 struct GoldenPlaygroundTest::GoldenPlaygroundTestImpl {
-  GoldenPlaygroundTestImpl()
-      : screenshoter_(new testing::MetalScreenshoter()) {}
-  std::unique_ptr<testing::MetalScreenshoter> screenshoter_;
-  ISize window_size_ = ISize{1024, 768};
+  GoldenPlaygroundTestImpl() : screenshoter(new testing::MetalScreenshoter()) {}
+  std::unique_ptr<testing::MetalScreenshoter> screenshoter;
+  ISize window_size = ISize{1024, 768};
 };
 
 GoldenPlaygroundTest::GoldenPlaygroundTest()
@@ -93,7 +92,7 @@ PlaygroundBackend GoldenPlaygroundTest::GetBackend() const {
 
 bool GoldenPlaygroundTest::OpenPlaygroundHere(const Picture& picture) {
   auto screenshot =
-      pimpl_->screenshoter_->MakeScreenshot(picture, pimpl_->window_size_);
+      pimpl_->screenshoter->MakeScreenshot(picture, pimpl_->window_size);
   return SaveScreenshot(std::move(screenshot));
 }
 
@@ -116,11 +115,11 @@ std::shared_ptr<Texture> GoldenPlaygroundTest::CreateTextureForFixture(
 }
 
 std::shared_ptr<Context> GoldenPlaygroundTest::GetContext() const {
-  return pimpl_->screenshoter_->GetContext().GetContext();
+  return pimpl_->screenshoter->GetContext().GetContext();
 }
 
 Point GoldenPlaygroundTest::GetContentScale() const {
-  return pimpl_->screenshoter_->GetPlayground().GetContentScale();
+  return pimpl_->screenshoter->GetPlayground().GetContentScale();
 }
 
 Scalar GoldenPlaygroundTest::GetSecondsElapsed() const {
@@ -128,7 +127,7 @@ Scalar GoldenPlaygroundTest::GetSecondsElapsed() const {
 }
 
 ISize GoldenPlaygroundTest::GetWindowSize() const {
-  return pimpl_->window_size_;
+  return pimpl_->window_size;
 }
 
 }  // namespace impeller

engine/src/flutter/impeller/golden_tests/golden_tests.cc

@@ -43,6 +43,7 @@ bool SaveScreenshot(std::unique_ptr<MetalScreenshot> screenshot) {
   return screenshot->WriteToPNG(
       WorkingDirectory::Instance()->GetFilenamePath(filename));
 }
+
 }  // namespace
 
 class GoldenTests : public ::testing::Test {

engine/src/flutter/impeller/golden_tests_harvester/bin/golden_tests_harvester.dart

@@ -23,7 +23,7 @@ class FakeSkiaGoldClient implements SkiaGoldClient {
       {double differentPixelsRate = 0.01,
       int pixelColorDelta = 0,
       required int screenshotSize}) async {
-    Logger.instance.log('addImg $testName ${goldenFile.path} $screenshotSize');
+    Logger.instance.log('addImg testName:$testName goldenFile:${goldenFile.path} screenshotSize:$screenshotSize differentPixelsRate:$differentPixelsRate pixelColorDelta:$pixelColorDelta');
   }
 
   @override

engine/src/flutter/impeller/golden_tests_harvester/lib/golden_tests_harvester.dart

@@ -32,9 +32,12 @@ Future<void> harvest(
     final String filename = (map['filename'] as String?)!;
     final int width = (map['width'] as int?)!;
     final int height = (map['height'] as int?)!;
+    final double maxDiffPixelsPercent = (map['maxDiffPixelsPercent'] as double?)!;
+    final int maxColorDelta = (map['maxColorDelta'] as int?)!;
     final File goldenImage = File(p.join(workDirectory.path, filename));
     final Future<void> future = skiaGoldClient
-        .addImg(filename, goldenImage, screenshotSize: width * height)
+        .addImg(filename, goldenImage,
+            screenshotSize: width * height, differentPixelsRate: maxDiffPixelsPercent, pixelColorDelta: maxColorDelta)
         .catchError((dynamic err) {
       Logger.instance.log('skia gold comparison failed: $err');
       throw Exception('Failed comparison: $filename');

engine/src/flutter/testing/skia_gold_client/lib/skia_gold_client.dart

@@ -178,15 +178,21 @@ class SkiaGoldClient {
   /// The [testName] and [goldenFile] parameters reference the current
   /// comparison being evaluated.
   ///
-  /// [pixelColorDelta] defines maximum acceptable difference in RGB channels of each pixel,
-  /// such that:
+  /// [pixelColorDelta] defines maximum acceptable difference in RGB channels of
+  /// each pixel, such that:
   ///
   /// ```
-  /// abs(r(image) - r(golden)) + abs(g(image) - g(golden)) + abs(b(image) - b(golden)) <= pixelDeltaThreshold
+  /// bool isSame(Color image, Color golden, int pixelDeltaThreshold) {
+  ///   return abs(image.r - golden.r)
+  ///     + abs(image.g - golden.g)
+  ///     + abs(image.b - golden.b) <= pixelDeltaThreshold;
+  /// }
   /// ```
   ///
-  /// [differentPixelsRate] is the fraction of accepted pixels to be wrong in the range [0.0, 1.0].
-  /// Defaults to 0.01. A value of 0.01 means that 1% of the pixels are allowed to change.
+  /// [differentPixelsRate] is the fraction of pixels that can differ, as
+  /// determined by the [pixelColorDelta] parameter. It's in the range [0.0,
+  /// 1.0] and defaults to 0.01. A value of 0.01 means that 1% of the pixels are
+  /// allowed to be different.
   Future<void> addImg(
     String testName,
     File goldenFile, {