macOS: Do not swap surface if nothing was painted (flutter#28136)

Author: knopp

shell/platform/darwin/macos/framework/Source/FlutterCompositor.h

@@ -46,7 +46,7 @@ class FlutterCompositor {
   // Present sets frame_started_ to false.
   virtual bool Present(const FlutterLayer** layers, size_t layers_count) = 0;
 
-  using PresentCallback = std::function<bool()>;
+  using PresentCallback = std::function<bool(bool has_flutter_content)>;
 
   // PresentCallback is called at the end of the Present function.
   void SetPresentCallback(const PresentCallback& present_callback);
@@ -73,7 +73,7 @@ class FlutterCompositor {
 
   // Calls the present callback and ensures the frame status is updated
   // to frame ended, returning whether the present was successful or not.
-  bool EndFrame();
+  bool EndFrame(bool has_flutter_content);
 
   // Creates a CALayer object which is backed by the supplied IOSurface, and
   // adds it to the root CALayer for this FlutterViewController's view.

shell/platform/darwin/macos/framework/Source/FlutterCompositor.mm

@@ -29,8 +29,8 @@
   SetFrameStatus(FrameStatus::kStarted);
 }
 
-bool FlutterCompositor::EndFrame() {
-  bool status = present_callback_();
+bool FlutterCompositor::EndFrame(bool has_flutter_content) {
+  bool status = present_callback_(has_flutter_content);
   SetFrameStatus(FrameStatus::kEnded);
   return status;
 }

shell/platform/darwin/macos/framework/Source/FlutterEngine.mm

@@ -340,21 +340,29 @@ - (FlutterCompositor*)createFlutterCompositor {
     FlutterMetalRenderer* metalRenderer = reinterpret_cast<FlutterMetalRenderer*>(_renderer);
     _macOSCompositor =
         std::make_unique<flutter::FlutterMetalCompositor>(_viewController, metalRenderer.device);
-    _macOSCompositor->SetPresentCallback([weakSelf]() {
-      FlutterMetalRenderer* metalRenderer =
-          reinterpret_cast<FlutterMetalRenderer*>(weakSelf.renderer);
-      return [metalRenderer present:0 /*=textureID*/];
+    _macOSCompositor->SetPresentCallback([weakSelf](bool has_flutter_content) {
+      if (has_flutter_content) {
+        FlutterMetalRenderer* metalRenderer =
+            reinterpret_cast<FlutterMetalRenderer*>(weakSelf.renderer);
+        return [metalRenderer present:0 /*=textureID*/] == YES;
+      } else {
+        return true;
+      }
     });
   } else {
     FlutterOpenGLRenderer* openGLRenderer = reinterpret_cast<FlutterOpenGLRenderer*>(_renderer);
     [openGLRenderer.openGLContext makeCurrentContext];
     _macOSCompositor = std::make_unique<flutter::FlutterGLCompositor>(_viewController,
                                                                       openGLRenderer.openGLContext);
 
-    _macOSCompositor->SetPresentCallback([weakSelf]() {
-      FlutterOpenGLRenderer* openGLRenderer =
-          reinterpret_cast<FlutterOpenGLRenderer*>(weakSelf.renderer);
-      return [openGLRenderer glPresent];
+    _macOSCompositor->SetPresentCallback([weakSelf](bool has_flutter_content) {
+      if (has_flutter_content) {
+        FlutterOpenGLRenderer* openGLRenderer =
+            reinterpret_cast<FlutterOpenGLRenderer*>(weakSelf.renderer);
+        return [openGLRenderer glPresent] == YES;
+      } else {
+        return true;
+      }
     });
   }
 

shell/platform/darwin/macos/framework/Source/FlutterEngineTest.mm

@@ -355,7 +355,7 @@ @interface FlutterEngine (Test)
   // Latch to ensure the entire layer tree has been generated and presented.
   fml::AutoResetWaitableEvent latch;
   auto compositor = engine.macOSCompositor;
-  compositor->SetPresentCallback([&]() {
+  compositor->SetPresentCallback([&](bool has_flutter_content) {
     latch.Signal();
     return true;
   });

shell/platform/darwin/macos/framework/Source/FlutterGLCompositor.mm

@@ -77,6 +77,8 @@
 bool FlutterGLCompositor::Present(const FlutterLayer** layers, size_t layers_count) {
   SetFrameStatus(FrameStatus::kPresenting);
 
+  bool has_flutter_content = false;
+
   for (size_t i = 0; i < layers_count; ++i) {
     const auto* layer = layers[i];
     FlutterBackingStore* backing_store = const_cast<FlutterBackingStore*>(layer->backing_store);
@@ -93,6 +95,7 @@
           // and needs to be flipped vertically
           InsertCALayerForIOSurface(io_surface, CATransform3DMakeScale(1, -1, 1));
         }
+        has_flutter_content = true;
         break;
       }
       case kFlutterLayerContentTypePlatformView:
@@ -102,7 +105,7 @@
     };
   }
 
-  return EndFrame();
+  return EndFrame(has_flutter_content);
 }
 
 }  // namespace flutter

shell/platform/darwin/macos/framework/Source/FlutterGLCompositorUnittests.mm

@@ -17,7 +17,7 @@
       std::make_unique<FlutterGLCompositor>(mockViewController, nullptr);
 
   bool flag = false;
-  macos_compositor->SetPresentCallback([f = &flag]() {
+  macos_compositor->SetPresentCallback([f = &flag](bool has_flutter_content) {
     *f = true;
     return true;
   });

shell/platform/darwin/macos/framework/Source/FlutterMetalCompositor.mm

@@ -76,6 +76,8 @@
 bool FlutterMetalCompositor::Present(const FlutterLayer** layers, size_t layers_count) {
   SetFrameStatus(FrameStatus::kPresenting);
 
+  bool has_flutter_content = false;
+
   for (size_t i = 0; i < layers_count; ++i) {
     const auto* layer = layers[i];
     FlutterBackingStore* backing_store = const_cast<FlutterBackingStore*>(layer->backing_store);
@@ -88,6 +90,7 @@
           IOSurfaceRef io_surface = [io_surface_holder ioSurface];
           InsertCALayerForIOSurface(io_surface);
         }
+        has_flutter_content = true;
         break;
       }
       case kFlutterLayerContentTypePlatformView:
@@ -97,7 +100,7 @@
     };
   }
 
-  return EndFrame();
+  return EndFrame(has_flutter_content);
 }
 
 }  // namespace flutter

shell/platform/darwin/macos/framework/Source/FlutterMetalCompositorUnittests.mm

@@ -17,7 +17,7 @@
       std::make_unique<FlutterMetalCompositor>(mockViewController, nullptr);
 
   bool flag = false;
-  macos_compositor->SetPresentCallback([f = &flag]() {
+  macos_compositor->SetPresentCallback([f = &flag](bool has_flutter_content) {
     *f = true;
     return true;
   });

shell/platform/darwin/macos/framework/Source/FlutterMetalSurfaceManagerTest.mm

@@ -53,6 +53,7 @@ - (instancetype)init {
   FlutterMetalSurfaceManager* surfaceManager = CreateSurfaceManager();
   CGSize size = CGSizeMake(100, 50);
   [surfaceManager ensureSurfaceSize:size];
+  [surfaceManager renderBuffer];  // make sure we have back buffer
   [surfaceManager swapBuffers];
   id<MTLTexture> texture =
       (reinterpret_cast<FlutterMetalRenderBackingStore*>([surfaceManager renderBuffer])).texture;

shell/platform/darwin/macos/framework/Source/FlutterSurfaceManager.mm

@@ -58,6 +58,13 @@ - (void)ensureSurfaceSize:(CGSize)size {
 }
 
 - (void)swapBuffers {
+#ifndef NDEBUG
+  // swapBuffers should not be called unless a frame was drawn
+  @synchronized(self) {
+    assert(_frameInProgress);
+  }
+#endif
+
   _contentLayer.frame = _containingLayer.bounds;
   _contentLayer.transform = _contentTransform;
   IOSurfaceRef contentIOSurface = [_ioSurfaces[kFlutterSurfaceManagerBackBuffer] ioSurface];