[iOS] Supported rendering platform views without merging the raster thread.

flow/embedded_views.cc

@@ -48,7 +48,8 @@ void ExternalViewEmbedder::SubmitFlutterView(
     int64_t flutter_view_id,
     GrDirectContext* context,
     const std::shared_ptr<impeller::AiksContext>& aiks_context,
-    std::unique_ptr<SurfaceFrame> frame) {
+    std::unique_ptr<SurfaceFrame> frame,
+    fml::RefPtr<fml::TaskRunner> platform_task_runner) {
   frame->Submit();
 }
 

flow/embedded_views.h

@@ -14,6 +14,7 @@
 #include "flutter/flow/surface_frame.h"
 #include "flutter/fml/memory/ref_counted.h"
 #include "flutter/fml/raster_thread_merger.h"
+#include "fml/task_runner.h"
 #include "third_party/skia/include/core/SkMatrix.h"
 #include "third_party/skia/include/core/SkPath.h"
 #include "third_party/skia/include/core/SkRRect.h"
@@ -459,7 +460,8 @@ class ExternalViewEmbedder {
       int64_t flutter_view_id,
       GrDirectContext* context,
       const std::shared_ptr<impeller::AiksContext>& aiks_context,
-      std::unique_ptr<SurfaceFrame> frame);
+      std::unique_ptr<SurfaceFrame> frame,
+      fml::RefPtr<fml::TaskRunner> platform_task_runner);
 
   // This method provides the embedder a way to do additional tasks after
   // |SubmitFrame|. For example, merge task runners if `should_resubmit_frame`

flow/surface_frame.h

@@ -14,6 +14,7 @@
 #include "flutter/fml/macros.h"
 #include "flutter/fml/time/time_point.h"
 
+#include "fml/synchronization/count_down_latch.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkSurface.h"
 
@@ -26,6 +27,9 @@ class SurfaceFrame {
   using SubmitCallback =
       std::function<bool(SurfaceFrame& surface_frame, DlCanvas* canvas)>;
 
+  using DeferredSubmit = std::function<bool()>;
+  using SubmitReciever = std::function<void(DeferredSubmit)>;
+
   // Information about the underlying framebuffer
   struct FramebufferInfo {
     // Indicates whether or not the surface supports pixel readback as used in
@@ -87,6 +91,8 @@ class SurfaceFrame {
     //
     // Defaults to true, which is generally a safe value.
     bool frame_boundary = true;
+
+    SubmitReciever submit_receiver;
   };
 
   bool Submit();

impeller/renderer/backend/metal/surface_mtl.h

@@ -8,6 +8,7 @@
 #include <QuartzCore/CAMetalLayer.h>
 #include <memory>
 
+#include "fml/synchronization/count_down_latch.h"
 #include "impeller/geometry/rect.h"
 #include "impeller/renderer/context.h"
 #include "impeller/renderer/surface.h"
@@ -58,6 +59,14 @@ class SurfaceMTL final : public Surface {
   // Returns a Rect defining the area of the surface in device pixels
   IRect coverage() const;
 
+  using DeferredSubmit = std::function<bool()>;
+  using SubmitReciever = std::function<void(DeferredSubmit)>;
+
+  void SetSubmitInfo(
+      const SubmitReciever& submit_reciever) {
+    submit_reciever_ = submit_reciever;
+  }
+
   // |Surface|
   bool Present() const override;
 
@@ -70,6 +79,8 @@ class SurfaceMTL final : public Surface {
   bool requires_blit_ = false;
   std::optional<IRect> clip_rect_;
 
+  SubmitReciever submit_reciever_;
+
   static bool ShouldPerformPartialRepaint(std::optional<IRect> damage_rect);
 
   SurfaceMTL(const std::weak_ptr<Context>& context,

impeller/renderer/backend/metal/surface_mtl.mm

@@ -294,6 +294,14 @@ - (void)flutterPrepareForPresent:(nonnull id<MTLCommandBuffer>)commandBuffer;
       [command_buffer waitUntilScheduled];
 #endif  // defined(FML_OS_IOS_SIMULATOR) && defined(FML_ARCH_CPU_X86_64)
       [drawable_ present];
+    } else if (submit_reciever_) {
+      auto drawable = drawable_;
+      [command_buffer commit];
+      [command_buffer waitUntilScheduled];
+      submit_reciever_([drawable]() -> bool {
+        [drawable present];
+        return true;
+      });
     } else {
       // The drawable may come from a FlutterMetalLayer, so it can't be
       // presented through the command buffer.

shell/common/rasterizer.cc

@@ -787,12 +787,11 @@ DrawSurfaceStatus Rasterizer::DrawToSurfaceUnsafe(
 
     frame->set_submit_info(submit_info);
 
-    if (external_view_embedder_ &&
-        (!raster_thread_merger_ || raster_thread_merger_->IsMerged())) {
+    if (external_view_embedder_) {
       FML_DCHECK(!frame->IsSubmitted());
       external_view_embedder_->SubmitFlutterView(
           view_id, surface_->GetContext(), surface_->GetAiksContext(),
-          std::move(frame));
+          std::move(frame), delegate_.GetTaskRunners().GetPlatformTaskRunner());
     } else {
       frame->Submit();
     }

shell/gpu/gpu_surface_metal_impeller.mm

@@ -155,6 +155,7 @@
         if (!surface) {
           return false;
         }
+        surface->SetSubmitInfo(surface_frame.submit_info().submit_receiver);
 
         if (clip_rect && clip_rect->IsEmpty()) {
           return surface->Present();
@@ -277,6 +278,8 @@
         auto surface =
             impeller::SurfaceMTL::MakeFromTexture(renderer->GetContext(), mtl_texture, clip_rect);
 
+        surface->SetSubmitInfo(surface_frame.submit_info().submit_receiver);
+
         if (clip_rect && clip_rect->IsEmpty()) {
           return surface->Present();
         }

shell/platform/android/external_view_embedder/external_view_embedder.h

@@ -13,6 +13,7 @@
 #include "flutter/shell/platform/android/external_view_embedder/surface_pool.h"
 #include "flutter/shell/platform/android/jni/platform_view_android_jni.h"
 #include "flutter/shell/platform/android/surface/android_surface.h"
+#include "fml/memory/ref_ptr.h"
 
 namespace flutter {
 
@@ -47,7 +48,8 @@ class AndroidExternalViewEmbedder final : public ExternalViewEmbedder {
       int64_t flutter_view_id,
       GrDirectContext* context,
       const std::shared_ptr<impeller::AiksContext>& aiks_context,
-      std::unique_ptr<SurfaceFrame> frame) override;
+      std::unique_ptr<SurfaceFrame> frame,
+      fml::RefPtr<fml::TaskRunner> platform_task_runner) override;
 
   // |ExternalViewEmbedder|
   PostPrerollResult PostPrerollAction(

shell/platform/darwin/ios/framework/Source/FlutterOverlayView.mm

@@ -12,7 +12,6 @@
 FLUTTER_ASSERT_ARC
 
 // This is mostly a duplication of FlutterView.
-// TODO(amirh): once GL support is in evaluate if we can merge this with FlutterView.
 @implementation FlutterOverlayView {
   fml::CFRef<CGColorSpaceRef> _colorSpaceRef;
 }