Fix damage calculation when not providing populate_existing_damage for gl embedder (flutter/engine#45611)

# Description

This PR fixes the `gl_populate_existing_damage` in embedder.cc, which currently returns an empty rectangle when a full repaint is needed. This leads to the `frame_damage` being considered empty in rasterizer.cc, causing incorrect partial repaint within Flutter when `gl_populate_existing_damage` is not provided by the embedder.

# Related Issue

https://github.com/flutter/flutter/issues/119601

# Tests

Add a new test. Also fixes damage calculation related tests in EmbedderTest by

* Use a new Dart embedder fixture entry point `render_gradient_retained` which retains the old layer to make sure layer tree diff happens.
* Add `latch.Wait()` after `SetGLPresentCallback` to make sure assertions have been executed.
* Make `existing_damage_rects` static since it should be valid after `populate_existing_damage` returns.

engine/src/flutter/shell/gpu/gpu_surface_gl_delegate.h

@@ -27,8 +27,6 @@ struct GLFrameInfo {
 struct GLFBOInfo {
   // The frame buffer's ID.
   uint32_t fbo_id;
-  // This boolean flags whether the returned FBO supports partial repaint.
-  const bool partial_repaint_enabled;
   // The frame buffer's existing damage (i.e. damage since it was last used).
   const std::optional<SkIRect> existing_damage;
 };

engine/src/flutter/shell/platform/android/android_surface_gl_skia.cc

@@ -166,7 +166,6 @@ GLFBOInfo AndroidSurfaceGLSkia::GLContextFBO(GLFrameInfo frame_info) const {
   // The default window bound framebuffer on Android.
   return GLFBOInfo{
       .fbo_id = 0,
-      .partial_repaint_enabled = onscreen_surface_->SupportsPartialRepaint(),
       .existing_damage = onscreen_surface_->InitialDamage(),
   };
 }

engine/src/flutter/shell/platform/embedder/embedder.cc

@@ -363,8 +363,7 @@ InferOpenGLPlatformViewCreationCallback(
     if (!populate_existing_damage) {
       return flutter::GLFBOInfo{
           .fbo_id = static_cast<uint32_t>(id),
-          .partial_repaint_enabled = false,
-          .existing_damage = SkIRect::MakeEmpty(),
+          .existing_damage = std::nullopt,
       };
     }
 
@@ -372,29 +371,22 @@ InferOpenGLPlatformViewCreationCallback(
     FlutterDamage existing_damage;
     populate_existing_damage(user_data, id, &existing_damage);
 
-    bool partial_repaint_enabled = true;
-    SkIRect existing_damage_rect;
+    std::optional<SkIRect> existing_damage_rect = std::nullopt;
 
     // Verify that at least one damage rectangle was provided.
     if (existing_damage.num_rects <= 0 || existing_damage.damage == nullptr) {
       FML_LOG(INFO) << "No damage was provided. Forcing full repaint.";
-      existing_damage_rect = SkIRect::MakeEmpty();
-      partial_repaint_enabled = false;
-    } else if (existing_damage.num_rects > 1) {
-      // Log message notifying users that multi-damage is not yet available in
-      // case they try to make use of it.
-      FML_LOG(INFO) << "Damage with multiple rectangles not yet supported. "
-                       "Repainting the whole frame.";
-      existing_damage_rect = SkIRect::MakeEmpty();
-      partial_repaint_enabled = false;
     } else {
-      existing_damage_rect = FlutterRectToSkIRect(*(existing_damage.damage));
+      existing_damage_rect = SkIRect::MakeEmpty();
+      for (size_t i = 0; i < existing_damage.num_rects; i++) {
+        existing_damage_rect->join(
+            FlutterRectToSkIRect(existing_damage.damage[i]));
+      }
     }
 
     // Pass the information about this FBO to the rendering backend.
     return flutter::GLFBOInfo{
         .fbo_id = static_cast<uint32_t>(id),
-        .partial_repaint_enabled = partial_repaint_enabled,
         .existing_damage = existing_damage_rect,
     };
   };

engine/src/flutter/shell/platform/embedder/fixtures/main.dart

@@ -1298,3 +1298,25 @@ void channel_listener_response() async {
   });
   signalNativeTest();
 }
+
+@pragma('vm:entry-point')
+void render_gradient_retained() {
+  OffsetEngineLayer? offsetLayer; // Retain the offset layer.
+  PlatformDispatcher.instance.onBeginFrame = (Duration duration) {
+    Size size = Size(800.0, 600.0);
+
+    SceneBuilder builder = SceneBuilder();
+
+    offsetLayer = builder.pushOffset(0.0, 0.0, oldLayer: offsetLayer);
+
+    // display_list_layer will comparing the display_list
+    // no need to retain the picture
+    builder.addPicture(
+        Offset(0.0, 0.0), CreateGradientBox(size)); // gradient - flutter
+
+    builder.pop();
+
+    PlatformDispatcher.instance.views.first.render(builder.build());
+  };
+  PlatformDispatcher.instance.scheduleFrame();
+}

engine/src/flutter/shell/platform/embedder/tests/embedder_gl_unittests.cc

@@ -3655,7 +3655,7 @@ TEST_F(EmbedderTest,
 
   EmbedderConfigBuilder builder(context);
   builder.SetOpenGLRendererConfig(SkISize::Make(800, 600));
-  builder.SetDartEntrypoint("render_gradient");
+  builder.SetDartEntrypoint("render_gradient_retained");
   builder.GetRendererConfig().open_gl.populate_existing_damage =
       [](void* context, const intptr_t id,
          FlutterDamage* existing_damage) -> void {
@@ -3668,7 +3668,8 @@ TEST_F(EmbedderTest,
       .SetGLPopulateExistingDamageCallback(
           [](const intptr_t id, FlutterDamage* existing_damage_ptr) {
             const size_t num_rects = 1;
-            FlutterRect existing_damage_rects[num_rects] = {
+            // The array must be valid after the callback returns.
+            static FlutterRect existing_damage_rects[num_rects] = {
                 FlutterRect{0, 0, 800, 600}};
             existing_damage_ptr->num_rects = num_rects;
             existing_damage_ptr->damage = existing_damage_rects;
@@ -3677,9 +3678,11 @@ TEST_F(EmbedderTest,
   auto engine = builder.LaunchEngine();
   ASSERT_TRUE(engine.is_valid());
 
+  fml::AutoResetWaitableEvent latch;
+
   // First frame should be entirely rerendered.
   static_cast<EmbedderTestContextGL&>(context).SetGLPresentCallback(
-      [](FlutterPresentInfo present_info) {
+      [&](FlutterPresentInfo present_info) {
         const size_t num_rects = 1;
         ASSERT_EQ(present_info.frame_damage.num_rects, num_rects);
         ASSERT_EQ(present_info.frame_damage.damage->left, 0);
@@ -3692,6 +3695,8 @@ TEST_F(EmbedderTest,
         ASSERT_EQ(present_info.buffer_damage.damage->top, 0);
         ASSERT_EQ(present_info.buffer_damage.damage->right, 800);
         ASSERT_EQ(present_info.buffer_damage.damage->bottom, 600);
+
+        latch.Signal();
       });
 
   // Send a window metrics events so frames may be scheduled.
@@ -3702,12 +3707,13 @@ TEST_F(EmbedderTest,
   event.pixel_ratio = 1.0;
   ASSERT_EQ(FlutterEngineSendWindowMetricsEvent(engine.get(), &event),
             kSuccess);
+  latch.Wait();
 
   // Because it's the same as the first frame, the second frame damage should
   // be empty but, because there was a full existing buffer damage, the buffer
   // damage should be the entire screen.
   static_cast<EmbedderTestContextGL&>(context).SetGLPresentCallback(
-      [](FlutterPresentInfo present_info) {
+      [&](FlutterPresentInfo present_info) {
         const size_t num_rects = 1;
         ASSERT_EQ(present_info.frame_damage.num_rects, num_rects);
         ASSERT_EQ(present_info.frame_damage.damage->left, 0);
@@ -3720,10 +3726,13 @@ TEST_F(EmbedderTest,
         ASSERT_EQ(present_info.buffer_damage.damage->top, 0);
         ASSERT_EQ(present_info.buffer_damage.damage->right, 800);
         ASSERT_EQ(present_info.buffer_damage.damage->bottom, 600);
+
+        latch.Signal();
       });
 
   ASSERT_EQ(FlutterEngineSendWindowMetricsEvent(engine.get(), &event),
             kSuccess);
+  latch.Wait();
 }
 
 TEST_F(EmbedderTest, PresentInfoReceivesEmptyDamage) {
@@ -3731,7 +3740,7 @@ TEST_F(EmbedderTest, PresentInfoReceivesEmptyDamage) {
 
   EmbedderConfigBuilder builder(context);
   builder.SetOpenGLRendererConfig(SkISize::Make(800, 600));
-  builder.SetDartEntrypoint("render_gradient");
+  builder.SetDartEntrypoint("render_gradient_retained");
   builder.GetRendererConfig().open_gl.populate_existing_damage =
       [](void* context, const intptr_t id,
          FlutterDamage* existing_damage) -> void {
@@ -3744,7 +3753,8 @@ TEST_F(EmbedderTest, PresentInfoReceivesEmptyDamage) {
       .SetGLPopulateExistingDamageCallback(
           [](const intptr_t id, FlutterDamage* existing_damage_ptr) {
             const size_t num_rects = 1;
-            FlutterRect existing_damage_rects[num_rects] = {
+            // The array must be valid after the callback returns.
+            static FlutterRect existing_damage_rects[num_rects] = {
                 FlutterRect{0, 0, 0, 0}};
             existing_damage_ptr->num_rects = num_rects;
             existing_damage_ptr->damage = existing_damage_rects;
@@ -3753,9 +3763,11 @@ TEST_F(EmbedderTest, PresentInfoReceivesEmptyDamage) {
   auto engine = builder.LaunchEngine();
   ASSERT_TRUE(engine.is_valid());
 
+  fml::AutoResetWaitableEvent latch;
+
   // First frame should be entirely rerendered.
   static_cast<EmbedderTestContextGL&>(context).SetGLPresentCallback(
-      [](FlutterPresentInfo present_info) {
+      [&](FlutterPresentInfo present_info) {
         const size_t num_rects = 1;
         ASSERT_EQ(present_info.frame_damage.num_rects, num_rects);
         ASSERT_EQ(present_info.frame_damage.damage->left, 0);
@@ -3768,6 +3780,8 @@ TEST_F(EmbedderTest, PresentInfoReceivesEmptyDamage) {
         ASSERT_EQ(present_info.buffer_damage.damage->top, 0);
         ASSERT_EQ(present_info.buffer_damage.damage->right, 800);
         ASSERT_EQ(present_info.buffer_damage.damage->bottom, 600);
+
+        latch.Signal();
       });
 
   // Send a window metrics events so frames may be scheduled.
@@ -3778,11 +3792,12 @@ TEST_F(EmbedderTest, PresentInfoReceivesEmptyDamage) {
   event.pixel_ratio = 1.0;
   ASSERT_EQ(FlutterEngineSendWindowMetricsEvent(engine.get(), &event),
             kSuccess);
+  latch.Wait();
 
   // Because it's the same as the first frame, the second frame should not be
   // rerendered assuming there is no existing damage.
   static_cast<EmbedderTestContextGL&>(context).SetGLPresentCallback(
-      [](FlutterPresentInfo present_info) {
+      [&](FlutterPresentInfo present_info) {
         const size_t num_rects = 1;
         ASSERT_EQ(present_info.frame_damage.num_rects, num_rects);
         ASSERT_EQ(present_info.frame_damage.damage->left, 0);
@@ -3795,10 +3810,13 @@ TEST_F(EmbedderTest, PresentInfoReceivesEmptyDamage) {
         ASSERT_EQ(present_info.buffer_damage.damage->top, 0);
         ASSERT_EQ(present_info.buffer_damage.damage->right, 0);
         ASSERT_EQ(present_info.buffer_damage.damage->bottom, 0);
+
+        latch.Signal();
       });
 
   ASSERT_EQ(FlutterEngineSendWindowMetricsEvent(engine.get(), &event),
             kSuccess);
+  latch.Wait();
 }
 
 TEST_F(EmbedderTest, PresentInfoReceivesPartialDamage) {
@@ -3806,7 +3824,7 @@ TEST_F(EmbedderTest, PresentInfoReceivesPartialDamage) {
 
   EmbedderConfigBuilder builder(context);
   builder.SetOpenGLRendererConfig(SkISize::Make(800, 600));
-  builder.SetDartEntrypoint("render_gradient");
+  builder.SetDartEntrypoint("render_gradient_retained");
   builder.GetRendererConfig().open_gl.populate_existing_damage =
       [](void* context, const intptr_t id,
          FlutterDamage* existing_damage) -> void {
@@ -3817,9 +3835,10 @@ TEST_F(EmbedderTest, PresentInfoReceivesPartialDamage) {
   // Return existing damage as only part of the screen on purpose.
   static_cast<EmbedderTestContextGL&>(context)
       .SetGLPopulateExistingDamageCallback(
-          [](const intptr_t id, FlutterDamage* existing_damage_ptr) {
+          [&](const intptr_t id, FlutterDamage* existing_damage_ptr) {
             const size_t num_rects = 1;
-            FlutterRect existing_damage_rects[num_rects] = {
+            // The array must be valid after the callback returns.
+            static FlutterRect existing_damage_rects[num_rects] = {
                 FlutterRect{200, 150, 400, 300}};
             existing_damage_ptr->num_rects = num_rects;
             existing_damage_ptr->damage = existing_damage_rects;
@@ -3828,9 +3847,11 @@ TEST_F(EmbedderTest, PresentInfoReceivesPartialDamage) {
   auto engine = builder.LaunchEngine();
   ASSERT_TRUE(engine.is_valid());
 
+  fml::AutoResetWaitableEvent latch;
+
   // First frame should be entirely rerendered.
   static_cast<EmbedderTestContextGL&>(context).SetGLPresentCallback(
-      [](FlutterPresentInfo present_info) {
+      [&](FlutterPresentInfo present_info) {
         const size_t num_rects = 1;
         ASSERT_EQ(present_info.frame_damage.num_rects, num_rects);
         ASSERT_EQ(present_info.frame_damage.damage->left, 0);
@@ -3843,6 +3864,8 @@ TEST_F(EmbedderTest, PresentInfoReceivesPartialDamage) {
         ASSERT_EQ(present_info.buffer_damage.damage->top, 0);
         ASSERT_EQ(present_info.buffer_damage.damage->right, 800);
         ASSERT_EQ(present_info.buffer_damage.damage->bottom, 600);
+
+        latch.Signal();
       });
 
   // Send a window metrics events so frames may be scheduled.
@@ -3853,12 +3876,13 @@ TEST_F(EmbedderTest, PresentInfoReceivesPartialDamage) {
   event.pixel_ratio = 1.0;
   ASSERT_EQ(FlutterEngineSendWindowMetricsEvent(engine.get(), &event),
             kSuccess);
+  latch.Wait();
 
   // Because it's the same as the first frame, the second frame damage should be
   // empty but, because there was a partial existing damage, the buffer damage
   // should represent that partial damage area.
   static_cast<EmbedderTestContextGL&>(context).SetGLPresentCallback(
-      [](FlutterPresentInfo present_info) {
+      [&](FlutterPresentInfo present_info) {
         const size_t num_rects = 1;
         ASSERT_EQ(present_info.frame_damage.num_rects, num_rects);
         ASSERT_EQ(present_info.frame_damage.damage->left, 0);
@@ -3871,10 +3895,13 @@ TEST_F(EmbedderTest, PresentInfoReceivesPartialDamage) {
         ASSERT_EQ(present_info.buffer_damage.damage->top, 150);
         ASSERT_EQ(present_info.buffer_damage.damage->right, 400);
         ASSERT_EQ(present_info.buffer_damage.damage->bottom, 300);
+
+        latch.Signal();
       });
 
   ASSERT_EQ(FlutterEngineSendWindowMetricsEvent(engine.get(), &event),
             kSuccess);
+  latch.Wait();
 }
 
 TEST_F(EmbedderTest, PopulateExistingDamageReceivesValidID) {
@@ -3882,7 +3909,7 @@ TEST_F(EmbedderTest, PopulateExistingDamageReceivesValidID) {
 
   EmbedderConfigBuilder builder(context);
   builder.SetOpenGLRendererConfig(SkISize::Make(800, 600));
-  builder.SetDartEntrypoint("render_gradient");
+  builder.SetDartEntrypoint("render_gradient_retained");
   builder.GetRendererConfig().open_gl.populate_existing_damage =
       [](void* context, const intptr_t id,
          FlutterDamage* existing_damage) -> void {
@@ -3900,6 +3927,8 @@ TEST_F(EmbedderTest, PopulateExistingDamageReceivesValidID) {
           [window_fbo_id = window_fbo_id](intptr_t id,
                                           FlutterDamage* existing_damage) {
             ASSERT_EQ(id, window_fbo_id);
+            existing_damage->num_rects = 0;
+            existing_damage->damage = nullptr;
           });
 
   // Send a window metrics events so frames may be scheduled.
@@ -3917,7 +3946,7 @@ TEST_F(EmbedderTest, PopulateExistingDamageReceivesInvalidID) {
 
   EmbedderConfigBuilder builder(context);
   builder.SetOpenGLRendererConfig(SkISize::Make(800, 600));
-  builder.SetDartEntrypoint("render_gradient");
+  builder.SetDartEntrypoint("render_gradient_retained");
   builder.GetRendererConfig().open_gl.populate_existing_damage =
       [](void* context, const intptr_t id,
          FlutterDamage* existing_damage) -> void {
@@ -3946,6 +3975,8 @@ TEST_F(EmbedderTest, PopulateExistingDamageReceivesInvalidID) {
           [window_fbo_id = window_fbo_id](intptr_t id,
                                           FlutterDamage* existing_damage) {
             ASSERT_NE(id, window_fbo_id);
+            existing_damage->num_rects = 0;
+            existing_damage->damage = nullptr;
           });
 
   // Send a window metrics events so frames may be scheduled.
@@ -4510,24 +4541,162 @@ TEST_F(EmbedderTest, ExternalTextureGLRefreshedTooOften) {
   glFinish();
 }
 
-TEST_F(EmbedderTest,
-       PresentInfoReceivesNoDamageWhenPopulateExistingDamageIsUndefined) {
+TEST_F(
+    EmbedderTest,
+    PresentInfoReceivesFullScreenDamageWhenPopulateExistingDamageIsNotProvided) {
   auto& context = GetEmbedderContext(EmbedderTestContextType::kOpenGLContext);
 
   EmbedderConfigBuilder builder(context);
   builder.SetOpenGLRendererConfig(SkISize::Make(800, 600));
-  builder.SetDartEntrypoint("render_gradient");
+  builder.SetDartEntrypoint("render_gradient_retained");
   builder.GetRendererConfig().open_gl.populate_existing_damage = nullptr;
 
   auto engine = builder.LaunchEngine();
   ASSERT_TRUE(engine.is_valid());
 
-  // No damage should be passed.
+  fml::AutoResetWaitableEvent latch;
+
+  // First frame should be entirely rerendered.
   static_cast<EmbedderTestContextGL&>(context).SetGLPresentCallback(
-      [](FlutterPresentInfo present_info) {
-        ASSERT_EQ(present_info.frame_damage.damage, nullptr);
-        ASSERT_EQ(present_info.buffer_damage.damage, nullptr);
+      [&](FlutterPresentInfo present_info) {
+        const size_t num_rects = 1;
+        ASSERT_EQ(present_info.frame_damage.num_rects, num_rects);
+        ASSERT_EQ(present_info.frame_damage.damage->left, 0);
+        ASSERT_EQ(present_info.frame_damage.damage->top, 0);
+        ASSERT_EQ(present_info.frame_damage.damage->right, 800);
+        ASSERT_EQ(present_info.frame_damage.damage->bottom, 600);
+
+        ASSERT_EQ(present_info.buffer_damage.num_rects, num_rects);
+        ASSERT_EQ(present_info.buffer_damage.damage->left, 0);
+        ASSERT_EQ(present_info.buffer_damage.damage->top, 0);
+        ASSERT_EQ(present_info.buffer_damage.damage->right, 800);
+        ASSERT_EQ(present_info.buffer_damage.damage->bottom, 600);
+
+        latch.Signal();
       });
+
+  // Send a window metrics events so frames may be scheduled.
+  FlutterWindowMetricsEvent event = {};
+  event.struct_size = sizeof(event);
+  event.width = 800;
+  event.height = 600;
+  event.pixel_ratio = 1.0;
+  ASSERT_EQ(FlutterEngineSendWindowMetricsEvent(engine.get(), &event),
+            kSuccess);
+  latch.Wait();
+
+  // Since populate_existing_damage is not provided, the partial repaint
+  // functionality is actually disabled. So, the next frame should be entirely
+  // new frame.
+  static_cast<EmbedderTestContextGL&>(context).SetGLPresentCallback(
+      [&](FlutterPresentInfo present_info) {
+        const size_t num_rects = 1;
+        ASSERT_EQ(present_info.frame_damage.num_rects, num_rects);
+        ASSERT_EQ(present_info.frame_damage.damage->left, 0);
+        ASSERT_EQ(present_info.frame_damage.damage->top, 0);
+        ASSERT_EQ(present_info.frame_damage.damage->right, 800);
+        ASSERT_EQ(present_info.frame_damage.damage->bottom, 600);
+
+        ASSERT_EQ(present_info.buffer_damage.num_rects, num_rects);
+        ASSERT_EQ(present_info.buffer_damage.damage->left, 0);
+        ASSERT_EQ(present_info.buffer_damage.damage->top, 0);
+        ASSERT_EQ(present_info.buffer_damage.damage->right, 800);
+        ASSERT_EQ(present_info.buffer_damage.damage->bottom, 600);
+
+        latch.Signal();
+      });
+
+  ASSERT_EQ(FlutterEngineSendWindowMetricsEvent(engine.get(), &event),
+            kSuccess);
+  latch.Wait();
+}
+
+TEST_F(EmbedderTest,
+       PresentInfoReceivesJoinedDamageWhenExistingDamageContainsMultipleRects) {
+  auto& context = GetEmbedderContext(EmbedderTestContextType::kOpenGLContext);
+
+  EmbedderConfigBuilder builder(context);
+  builder.SetOpenGLRendererConfig(SkISize::Make(800, 600));
+  builder.SetDartEntrypoint("render_gradient_retained");
+  builder.GetRendererConfig().open_gl.populate_existing_damage =
+      [](void* context, const intptr_t id,
+         FlutterDamage* existing_damage) -> void {
+    return reinterpret_cast<EmbedderTestContextGL*>(context)
+        ->GLPopulateExistingDamage(id, existing_damage);
+  };
+
+  // Return existing damage as the entire screen on purpose.
+  static_cast<EmbedderTestContextGL&>(context)
+      .SetGLPopulateExistingDamageCallback(
+          [](const intptr_t id, FlutterDamage* existing_damage_ptr) {
+            const size_t num_rects = 2;
+            // The array must be valid after the callback returns.
+            static FlutterRect existing_damage_rects[num_rects] = {
+                FlutterRect{100, 150, 200, 250},
+                FlutterRect{200, 250, 300, 350},
+            };
+            existing_damage_ptr->num_rects = num_rects;
+            existing_damage_ptr->damage = existing_damage_rects;
+          });
+
+  auto engine = builder.LaunchEngine();
+  ASSERT_TRUE(engine.is_valid());
+
+  fml::AutoResetWaitableEvent latch;
+
+  // First frame should be entirely rerendered.
+  static_cast<EmbedderTestContextGL&>(context).SetGLPresentCallback(
+      [&](FlutterPresentInfo present_info) {
+        const size_t num_rects = 1;
+        ASSERT_EQ(present_info.frame_damage.num_rects, num_rects);
+        ASSERT_EQ(present_info.frame_damage.damage->left, 0);
+        ASSERT_EQ(present_info.frame_damage.damage->top, 0);
+        ASSERT_EQ(present_info.frame_damage.damage->right, 800);
+        ASSERT_EQ(present_info.frame_damage.damage->bottom, 600);
+
+        ASSERT_EQ(present_info.buffer_damage.num_rects, num_rects);
+        ASSERT_EQ(present_info.buffer_damage.damage->left, 0);
+        ASSERT_EQ(present_info.buffer_damage.damage->top, 0);
+        ASSERT_EQ(present_info.buffer_damage.damage->right, 800);
+        ASSERT_EQ(present_info.buffer_damage.damage->bottom, 600);
+
+        latch.Signal();
+      });
+
+  // Send a window metrics events so frames may be scheduled.
+  FlutterWindowMetricsEvent event = {};
+  event.struct_size = sizeof(event);
+  event.width = 800;
+  event.height = 600;
+  event.pixel_ratio = 1.0;
+  ASSERT_EQ(FlutterEngineSendWindowMetricsEvent(engine.get(), &event),
+            kSuccess);
+  latch.Wait();
+
+  // Because it's the same as the first frame, the second frame damage should
+  // be empty but, because there was a full existing buffer damage, the buffer
+  // damage should be the entire screen.
+  static_cast<EmbedderTestContextGL&>(context).SetGLPresentCallback(
+      [&](FlutterPresentInfo present_info) {
+        const size_t num_rects = 1;
+        ASSERT_EQ(present_info.frame_damage.num_rects, num_rects);
+        ASSERT_EQ(present_info.frame_damage.damage->left, 0);
+        ASSERT_EQ(present_info.frame_damage.damage->top, 0);
+        ASSERT_EQ(present_info.frame_damage.damage->right, 0);
+        ASSERT_EQ(present_info.frame_damage.damage->bottom, 0);
+
+        ASSERT_EQ(present_info.buffer_damage.num_rects, num_rects);
+        ASSERT_EQ(present_info.buffer_damage.damage->left, 100);
+        ASSERT_EQ(present_info.buffer_damage.damage->top, 150);
+        ASSERT_EQ(present_info.buffer_damage.damage->right, 300);
+        ASSERT_EQ(present_info.buffer_damage.damage->bottom, 350);
+
+        latch.Signal();
+      });
+
+  ASSERT_EQ(FlutterEngineSendWindowMetricsEvent(engine.get(), &event),
+            kSuccess);
+  latch.Wait();
 }
 
 INSTANTIATE_TEST_SUITE_P(