Do not override partial repaint support globally (flutter/engine#35539)

engine/src/flutter/flow/surface_frame.h

@@ -51,7 +51,7 @@ class SurfaceFrame {
     // If existing damage is unspecified (nullopt), entire frame will be
     // rasterized (no partial redraw). To signal that there is no existing
     // damage use an empty SkIRect.
-    std::optional<SkIRect> existing_damage;
+    std::optional<SkIRect> existing_damage = std::nullopt;
   };
 
   SurfaceFrame(sk_sp<SkSurface> surface,

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

@@ -30,7 +30,7 @@ struct GLFBOInfo {
   // 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 SkIRect existing_damage;
+  const std::optional<SkIRect> existing_damage;
 };
 
 // Information passed during presentation of a frame.

engine/src/flutter/shell/gpu/gpu_surface_gl_skia.cc

@@ -196,7 +196,6 @@ bool GPUSurfaceGLSkia::CreateOrUpdateSurfaces(const SkISize& size) {
 
   onscreen_surface_ = std::move(onscreen_surface);
   fbo_id_ = fbo_info.fbo_id;
-  supports_partial_repaint_ = fbo_info.partial_repaint_enabled;
   existing_damage_ = fbo_info.existing_damage;
 
   return true;
@@ -250,9 +249,9 @@ std::unique_ptr<SurfaceFrame> GPUSurfaceGLSkia::AcquireFrame(
       };
 
   framebuffer_info = delegate_->GLContextFramebufferInfo();
-  // Partial repaint is enabled by default
-  framebuffer_info.supports_partial_repaint = supports_partial_repaint_;
-  framebuffer_info.existing_damage = existing_damage_;
+  if (!framebuffer_info.existing_damage.has_value()) {
+    framebuffer_info.existing_damage = existing_damage_;
+  }
   return std::make_unique<SurfaceFrame>(surface, std::move(framebuffer_info),
                                         submit_callback,
                                         std::move(context_switch));
@@ -303,7 +302,6 @@ bool GPUSurfaceGLSkia::PresentSurface(const SurfaceFrame& frame,
 
     onscreen_surface_ = std::move(new_onscreen_surface);
     fbo_id_ = fbo_info.fbo_id;
-    supports_partial_repaint_ = fbo_info.partial_repaint_enabled;
     existing_damage_ = fbo_info.existing_damage;
   }
 

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

@@ -67,8 +67,10 @@ class GPUSurfaceGLSkia : public Surface {
   sk_sp<SkSurface> onscreen_surface_;
   /// FBO backing the current `onscreen_surface_`.
   uint32_t fbo_id_ = 0;
-  // Private variable used to keep track of the current FBO's existing damage.
-  SkIRect existing_damage_ = SkIRect::MakeEmpty();
+  // The current FBO's existing damage, as tracked by the GPU surface, delegates
+  // still have an option of overriding this damage with their own in
+  // `GLContextFrameBufferInfo`.
+  std::optional<SkIRect> existing_damage_ = std::nullopt;
   bool context_owner_ = false;
   // TODO(38466): Refactor GPU surface APIs take into account the fact that an
   // external view embedder may want to render to the root surface. This is a
@@ -76,8 +78,6 @@ class GPUSurfaceGLSkia : public Surface {
   // external view embedder is present.
   const bool render_to_surface_ = true;
   bool valid_ = false;
-  // Partial repaint is on by default.
-  bool supports_partial_repaint_ = true;
 
   // WeakPtrFactory must be the last member.
   fml::TaskRunnerAffineWeakPtrFactory<GPUSurfaceGLSkia> weak_factory_;

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

@@ -167,6 +167,8 @@ 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_surface_gl.cc

@@ -80,6 +80,17 @@ EmbedderSurfaceGL::GLProcResolver EmbedderSurfaceGL::GetGLProcResolver() const {
   return gl_dispatch_table_.gl_proc_resolver;
 }
 
+// |GPUSurfaceGLDelegate|
+SurfaceFrame::FramebufferInfo EmbedderSurfaceGL::GLContextFramebufferInfo()
+    const {
+  // Enable partial repaint by default on the embedders.
+  auto info = SurfaceFrame::FramebufferInfo{};
+  info.supports_readback = true;
+  info.supports_partial_repaint =
+      gl_dispatch_table_.gl_populate_existing_damage != nullptr;
+  return info;
+}
+
 // |EmbedderSurface|
 std::unique_ptr<Surface> EmbedderSurfaceGL::CreateGPUSurface() {
   const bool render_to_surface = !external_view_embedder_;

engine/src/flutter/shell/platform/embedder/embedder_surface_gl.h

@@ -71,6 +71,9 @@ class EmbedderSurfaceGL final : public EmbedderSurface,
   // |GPUSurfaceGLDelegate|
   GLProcResolver GetGLProcResolver() const override;
 
+  // |GPUSurfaceGLDelegate|
+  SurfaceFrame::FramebufferInfo GLContextFramebufferInfo() const override;
+
   FML_DISALLOW_COPY_AND_ASSIGN(EmbedderSurfaceGL);
 };
 

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

@@ -4065,6 +4065,26 @@ TEST_F(EmbedderTest, ExternalTextureGLRefreshedTooOften) {
   EXPECT_TRUE(resolve_called);
 }
 
+TEST_F(EmbedderTest,
+       PresentInfoReceivesNoDamageWhenPopulateExistingDamageIsUndefined) {
+  auto& context = GetEmbedderContext(EmbedderTestContextType::kOpenGLContext);
+
+  EmbedderConfigBuilder builder(context);
+  builder.SetOpenGLRendererConfig(SkISize::Make(800, 600));
+  builder.SetDartEntrypoint("render_gradient");
+  builder.GetRendererConfig().open_gl.populate_existing_damage = nullptr;
+
+  auto engine = builder.LaunchEngine();
+  ASSERT_TRUE(engine.is_valid());
+
+  // No damage should be passed.
+  static_cast<EmbedderTestContextGL&>(context).SetGLPresentCallback(
+      [](FlutterPresentInfo present_info) {
+        ASSERT_EQ(present_info.frame_damage.damage, nullptr);
+        ASSERT_EQ(present_info.buffer_damage.damage, nullptr);
+      });
+}
+
 INSTANTIATE_TEST_SUITE_P(
     EmbedderTestGlVk,
     EmbedderTestMultiBackend,