Apply changes to the embedded UIView tree when presenting a frame (#6712)

Also tracks the order of embedded views from frame to frame, and only
removes and reattaches subviews if there is a structural change to the
UIView hierarchy.

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

@@ -396,10 +396,6 @@
   return _shell->Screenshot(type, base64Encode);
 }
 
-- (flow::ExternalViewEmbedder*)externalViewEmbedder {
-  return _platformViewsController.get();
-}
-
 #pragma mark - FlutterBinaryMessenger
 
 - (void)sendOnChannel:(NSString*)channel message:(NSData*)message {

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

@@ -66,8 +66,6 @@ void FlutterPlatformViewsController::OnCreate(FlutterMethodCall* call, FlutterRe
                flutterView:flutter_view_] autorelease];
   views_[viewId] = fml::scoped_nsobject<FlutterTouchInterceptingView>([view retain]);
 
-  UIView* flutter_view = flutter_view_.get();
-  [flutter_view addSubview:views_[viewId].get()];
   result(nil);
 }
 
@@ -127,6 +125,33 @@ void FlutterPlatformViewsController::CompositeEmbeddedView(int view_id,
 
   UIView* view = views_[view_id];
   [view setFrame:rect];
+  composition_order_.push_back(view_id);
+}
+
+void FlutterPlatformViewsController::Present() {
+  if (composition_order_ == active_composition_order_) {
+    composition_order_.clear();
+    return;
+  }
+  UIView* flutter_view = flutter_view_.get();
+
+  // This can be more efficient, instead of removing all views and then re-attaching them,
+  // we should only remove the views that has been completly removed from the layer tree, and
+  // reorder the views using UIView's bringSubviewToFront.
+  // TODO(amirh): make this more efficient.
+  // https://github.com/flutter/flutter/issues/23793
+  for (UIView* sub_view in [flutter_view subviews]) {
+    [sub_view removeFromSuperview];
+  }
+
+  active_composition_order_.clear();
+  for (size_t i = 0; i < composition_order_.size(); i++) {
+    int view_id = composition_order_[i];
+    [flutter_view addSubview:views_[view_id].get()];
+    active_composition_order_.push_back(view_id);
+  }
+
+  composition_order_.clear();
 }
 
 }  // namespace shell

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h

@@ -26,7 +26,7 @@
 
 namespace shell {
 
-class FlutterPlatformViewsController : public flow::ExternalViewEmbedder {
+class FlutterPlatformViewsController {
  public:
   FlutterPlatformViewsController() = default;
 
@@ -36,6 +36,8 @@ class FlutterPlatformViewsController : public flow::ExternalViewEmbedder {
 
   void CompositeEmbeddedView(int view_id, const flow::EmbeddedViewParams& params);
 
+  void Present();
+
   void OnMethodCall(FlutterMethodCall* call, FlutterResult& result);
 
  private:
@@ -44,6 +46,13 @@ class FlutterPlatformViewsController : public flow::ExternalViewEmbedder {
   std::map<std::string, fml::scoped_nsobject<NSObject<FlutterPlatformViewFactory>>> factories_;
   std::map<int64_t, fml::scoped_nsobject<FlutterTouchInterceptingView>> views_;
 
+  // A vector of embedded view IDs according to their composition order.
+  // The last ID in this vector belond to the that is composited on top of all others.
+  std::vector<int64_t> composition_order_;
+
+  // The latest composition order that was presented in Present().
+  std::vector<int64_t> active_composition_order_;
+
   void OnCreate(FlutterMethodCall* call, FlutterResult& result);
   void OnDispose(FlutterMethodCall* call, FlutterResult& result);
   void OnAcceptGesture(FlutterMethodCall* call, FlutterResult& result);

shell/platform/darwin/ios/framework/Source/FlutterView.h

@@ -11,7 +11,6 @@
 
 #import "FlutterPlatformViews_Internal.h"
 
-#include "flutter/flow/embedded_views.h"
 #include "flutter/fml/memory/weak_ptr.h"
 #include "flutter/shell/common/shell.h"
 #include "flutter/shell/platform/darwin/ios/ios_surface.h"
@@ -21,7 +20,7 @@
 - (shell::Rasterizer::Screenshot)takeScreenshot:(shell::Rasterizer::ScreenshotType)type
                                 asBase64Encoded:(BOOL)base64Encode;
 
-- (flow::ExternalViewEmbedder*)externalViewEmbedder;
+- (shell::FlutterPlatformViewsController*)platformViewsController;
 
 @end
 

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

@@ -80,11 +80,11 @@ id<FlutterViewEngineDelegate> _delegate;
     fml::scoped_nsobject<CAEAGLLayer> eagl_layer(
         reinterpret_cast<CAEAGLLayer*>([self.layer retain]));
     return std::make_unique<shell::IOSSurfaceGL>(std::move(eagl_layer),
-                                                 *[_delegate externalViewEmbedder]);
+                                                 *[_delegate platformViewsController]);
   } else {
     fml::scoped_nsobject<CALayer> layer(reinterpret_cast<CALayer*>([self.layer retain]));
     return std::make_unique<shell::IOSSurfaceSoftware>(std::move(layer),
-                                                       *[_delegate externalViewEmbedder]);
+                                                       *[_delegate platformViewsController]);
   }
 }
 

shell/platform/darwin/ios/ios_surface.h

@@ -5,6 +5,8 @@
 #ifndef FLUTTER_SHELL_PLATFORM_DARWIN_IOS_IOS_SURFACE_H_
 #define FLUTTER_SHELL_PLATFORM_DARWIN_IOS_IOS_SURFACE_H_
 
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h"
+
 #include <memory>
 
 #include "flutter/fml/macros.h"
@@ -15,7 +17,7 @@ namespace shell {
 
 class IOSSurface {
  public:
-  IOSSurface();
+  IOSSurface(FlutterPlatformViewsController& platform_views_controller);
 
   virtual ~IOSSurface();
 
@@ -27,6 +29,12 @@ class IOSSurface {
 
   virtual std::unique_ptr<Surface> CreateGPUSurface() = 0;
 
+ protected:
+  FlutterPlatformViewsController& GetPlatformViewsController();
+
+ private:
+  FlutterPlatformViewsController& platform_views_controller_;
+
  public:
   FML_DISALLOW_COPY_AND_ASSIGN(IOSSurface);
 };

shell/platform/darwin/ios/ios_surface.mm

@@ -11,8 +11,12 @@
 
 namespace shell {
 
-IOSSurface::IOSSurface() = default;
+IOSSurface::IOSSurface(FlutterPlatformViewsController& platform_views_controller)
+    : platform_views_controller_(platform_views_controller) {}
 
 IOSSurface::~IOSSurface() = default;
 
+FlutterPlatformViewsController& IOSSurface::GetPlatformViewsController() {
+  return platform_views_controller_;
+}
 }  // namespace shell

shell/platform/darwin/ios/ios_surface_gl.h

@@ -15,10 +15,12 @@
 
 namespace shell {
 
-class IOSSurfaceGL : public IOSSurface, public GPUSurfaceGLDelegate {
+class IOSSurfaceGL : public IOSSurface,
+                     public GPUSurfaceGLDelegate,
+                     public flow::ExternalViewEmbedder {
  public:
   IOSSurfaceGL(fml::scoped_nsobject<CAEAGLLayer> layer,
-               flow::ExternalViewEmbedder& external_view_embedder);
+               FlutterPlatformViewsController& platform_views_controller);
 
   ~IOSSurfaceGL() override;
 
@@ -43,11 +45,12 @@ class IOSSurfaceGL : public IOSSurface, public GPUSurfaceGLDelegate {
   // |shell::GPUSurfaceGLDelegate|
   flow::ExternalViewEmbedder* GetExternalViewEmbedder() override;
 
+  // |flow::ExternalViewEmbedder|
+  void CompositeEmbeddedView(int view_id, const flow::EmbeddedViewParams& params) override;
+
  private:
   IOSGLContext context_;
 
-  flow::ExternalViewEmbedder& external_view_embedder_;
-
   FML_DISALLOW_COPY_AND_ASSIGN(IOSSurfaceGL);
 };
 

shell/platform/darwin/ios/ios_surface_gl.mm

@@ -10,8 +10,8 @@
 namespace shell {
 
 IOSSurfaceGL::IOSSurfaceGL(fml::scoped_nsobject<CAEAGLLayer> layer,
-                           flow::ExternalViewEmbedder& view_embedder)
-    : context_(std::move(layer)), external_view_embedder_(view_embedder) {}
+                           FlutterPlatformViewsController& platform_views_controller)
+    : IOSSurface(platform_views_controller), context_(std::move(layer)) {}
 
 IOSSurfaceGL::~IOSSurfaceGL() = default;
 
@@ -55,11 +55,20 @@ bool IOSSurfaceGL::GLContextClearCurrent() {
 
 bool IOSSurfaceGL::GLContextPresent() {
   TRACE_EVENT0("flutter", "IOSSurfaceGL::GLContextPresent");
-  return IsValid() ? context_.PresentRenderBuffer() : false;
+  if (!IsValid() || !context_.PresentRenderBuffer()) {
+    return false;
+  }
+
+  GetPlatformViewsController().Present();
+  return true;
 }
 
 flow::ExternalViewEmbedder* IOSSurfaceGL::GetExternalViewEmbedder() {
-  return &external_view_embedder_;
+  return this;
+}
+
+void IOSSurfaceGL::CompositeEmbeddedView(int view_id, const flow::EmbeddedViewParams& params) {
+  GetPlatformViewsController().CompositeEmbeddedView(view_id, params);
 }
 
 }  // namespace shell

shell/platform/darwin/ios/ios_surface_software.h

@@ -5,6 +5,7 @@
 #ifndef FLUTTER_SHELL_PLATFORM_DARWIN_IOS_IOS_SURFACE_SOFTWARE_H_
 #define FLUTTER_SHELL_PLATFORM_DARWIN_IOS_IOS_SURFACE_SOFTWARE_H_
 
+#include "flutter/flow/embedded_views.h"
 #include "flutter/fml/macros.h"
 #include "flutter/fml/platform/darwin/scoped_nsobject.h"
 #include "flutter/shell/gpu/gpu_surface_software.h"
@@ -14,10 +15,12 @@
 
 namespace shell {
 
-class IOSSurfaceSoftware final : public IOSSurface, public GPUSurfaceSoftwareDelegate {
+class IOSSurfaceSoftware final : public IOSSurface,
+                                 public GPUSurfaceSoftwareDelegate,
+                                 public flow::ExternalViewEmbedder {
  public:
   IOSSurfaceSoftware(fml::scoped_nsobject<CALayer> layer,
-                     flow::ExternalViewEmbedder& view_embedder);
+                     FlutterPlatformViewsController& platform_views_controller);
 
   ~IOSSurfaceSoftware() override;
 
@@ -42,9 +45,11 @@ class IOSSurfaceSoftware final : public IOSSurface, public GPUSurfaceSoftwareDel
   // |shell::GPUSurfaceSoftwareDelegate|
   flow::ExternalViewEmbedder* GetExternalViewEmbedder() override;
 
+  // |flow::ExternalViewEmbedder|
+  void CompositeEmbeddedView(int view_id, const flow::EmbeddedViewParams& params) override;
+
  private:
   fml::scoped_nsobject<CALayer> layer_;
-  flow::ExternalViewEmbedder& external_view_embedder_;
   sk_sp<SkSurface> sk_surface_;
 
   FML_DISALLOW_COPY_AND_ASSIGN(IOSSurfaceSoftware);

shell/platform/darwin/ios/ios_surface_software.mm

@@ -16,8 +16,8 @@
 namespace shell {
 
 IOSSurfaceSoftware::IOSSurfaceSoftware(fml::scoped_nsobject<CALayer> layer,
-                                       flow::ExternalViewEmbedder& view_embedder)
-    : layer_(std::move(layer)), external_view_embedder_(view_embedder) {
+                                       FlutterPlatformViewsController& platform_views_controller)
+    : IOSSurface(platform_views_controller), layer_(std::move(layer)) {
   UpdateStorageSizeIfNecessary();
 }
 
@@ -123,11 +123,17 @@ bool IOSSurfaceSoftware::PresentBackingStore(sk_sp<SkSurface> backing_store) {
 
   layer_.get().contents = reinterpret_cast<id>(static_cast<CGImageRef>(pixmap_image));
 
+  GetPlatformViewsController().Present();
+
   return true;
 }
 
 flow::ExternalViewEmbedder* IOSSurfaceSoftware::GetExternalViewEmbedder() {
-  return &external_view_embedder_;
+  return this;
+}
+void IOSSurfaceSoftware::CompositeEmbeddedView(int view_id,
+                                               const flow::EmbeddedViewParams& params) {
+  GetPlatformViewsController().CompositeEmbeddedView(view_id, params);
 }
 
 }  // namespace shell