FlutterPlatformViews.mm

// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#import <UIKit/UIGestureRecognizerSubclass.h>

#include <list>
#include <map>
#include <memory>
#include <string>

#include "flutter/common/graphics/persistent_cache.h"
#include "flutter/flow/rtree.h"
#include "flutter/fml/platform/darwin/scoped_nsobject.h"
#import "flutter/shell/platform/darwin/common/framework/Headers/FlutterChannels.h"
#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterOverlayView.h"
#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h"
#import "flutter/shell/platform/darwin/ios/ios_surface.h"
#import "flutter/shell/platform/darwin/ios/ios_surface_gl.h"

namespace flutter {

std::shared_ptr<FlutterPlatformViewLayer> FlutterPlatformViewLayerPool::GetLayer(
    GrDirectContext* gr_context,
    std::shared_ptr<IOSContext> ios_context) {
  if (available_layer_index_ >= layers_.size()) {
    std::shared_ptr<FlutterPlatformViewLayer> layer;
    fml::scoped_nsobject<FlutterOverlayView> overlay_view;
    fml::scoped_nsobject<FlutterOverlayView> overlay_view_wrapper;

    if (!gr_context) {
      overlay_view.reset([[FlutterOverlayView alloc] init]);
      overlay_view_wrapper.reset([[FlutterOverlayView alloc] init]);

      auto ca_layer = fml::scoped_nsobject<CALayer>{[[overlay_view.get() layer] retain]};
      std::unique_ptr<IOSSurface> ios_surface = IOSSurface::Create(ios_context, ca_layer);
      std::unique_ptr<Surface> surface = ios_surface->CreateGPUSurface();

      layer = std::make_shared<FlutterPlatformViewLayer>(
          std::move(overlay_view), std::move(overlay_view_wrapper), std::move(ios_surface),
          std::move(surface));
    } else {
      CGFloat screenScale = [UIScreen mainScreen].scale;
      overlay_view.reset([[FlutterOverlayView alloc] initWithContentsScale:screenScale]);
      overlay_view_wrapper.reset([[FlutterOverlayView alloc] initWithContentsScale:screenScale]);

      auto ca_layer = fml::scoped_nsobject<CALayer>{[[overlay_view.get() layer] retain]};
      std::unique_ptr<IOSSurface> ios_surface = IOSSurface::Create(ios_context, ca_layer);
      std::unique_ptr<Surface> surface = ios_surface->CreateGPUSurface(gr_context);

      layer = std::make_shared<FlutterPlatformViewLayer>(
          std::move(overlay_view), std::move(overlay_view_wrapper), std::move(ios_surface),
          std::move(surface));
      layer->gr_context = gr_context;
    }
    // The overlay view wrapper masks the overlay view.
    // This is required to keep the backing surface size unchanged between frames.
    //
    // Otherwise, changing the size of the overlay would require a new surface,
    // which can be very expensive.
    //
    // This is the case of an animation in which the overlay size is changing in every frame.
    //
    // +------------------------+
    // |   overlay_view         |
    // |    +--------------+    |              +--------------+
    // |    |    wrapper   |    |  == mask =>  | overlay_view |
    // |    +--------------+    |              +--------------+
    // +------------------------+
    overlay_view_wrapper.get().clipsToBounds = YES;
    [overlay_view_wrapper.get() addSubview:overlay_view];
    layers_.push_back(layer);
  }
  std::shared_ptr<FlutterPlatformViewLayer> layer = layers_[available_layer_index_];
  if (gr_context != layer->gr_context) {
    layer->gr_context = gr_context;
    // The overlay already exists, but the GrContext was changed so we need to recreate
    // the rendering surface with the new GrContext.
    IOSSurface* ios_surface = layer->ios_surface.get();
    std::unique_ptr<Surface> surface = ios_surface->CreateGPUSurface(gr_context);
    layer->surface = std::move(surface);
  }
  available_layer_index_++;
  return layer;
}

void FlutterPlatformViewLayerPool::RecycleLayers() {
  available_layer_index_ = 0;
}

std::vector<std::shared_ptr<FlutterPlatformViewLayer>>
FlutterPlatformViewLayerPool::GetUnusedLayers() {
  std::vector<std::shared_ptr<FlutterPlatformViewLayer>> results;
  for (size_t i = available_layer_index_; i < layers_.size(); i++) {
    results.push_back(layers_[i]);
  }
  return results;
}

void FlutterPlatformViewsController::SetFlutterView(UIView* flutter_view) {
  flutter_view_.reset([flutter_view retain]);
}

void FlutterPlatformViewsController::SetFlutterViewController(
    UIViewController* flutter_view_controller) {
  flutter_view_controller_.reset([flutter_view_controller retain]);
}

UIViewController* FlutterPlatformViewsController::getFlutterViewController() {
  return flutter_view_controller_.get();
}

void FlutterPlatformViewsController::OnMethodCall(FlutterMethodCall* call, FlutterResult& result) {
  if ([[call method] isEqualToString:@"create"]) {
    OnCreate(call, result);
  } else if ([[call method] isEqualToString:@"dispose"]) {
    OnDispose(call, result);
  } else if ([[call method] isEqualToString:@"acceptGesture"]) {
    OnAcceptGesture(call, result);
  } else if ([[call method] isEqualToString:@"rejectGesture"]) {
    OnRejectGesture(call, result);
  } else {
    result(FlutterMethodNotImplemented);
  }
}

void FlutterPlatformViewsController::OnCreate(FlutterMethodCall* call, FlutterResult& result) {
  NSDictionary<NSString*, id>* args = [call arguments];

  long viewId = [args[@"id"] longValue];
  std::string viewType([args[@"viewType"] UTF8String]);

  if (views_.count(viewId) != 0) {
    result([FlutterError errorWithCode:@"recreating_view"
                               message:@"trying to create an already created view"
                               details:[NSString stringWithFormat:@"view id: '%ld'", viewId]]);
  }

  NSObject<FlutterPlatformViewFactory>* factory = factories_[viewType].get();
  if (factory == nil) {
    result([FlutterError errorWithCode:@"unregistered_view_type"
                               message:@"trying to create a view with an unregistered type"
                               details:[NSString stringWithFormat:@"unregistered view type: '%@'",
                                                                  args[@"viewType"]]]);
    return;
  }

  id params = nil;
  if ([factory respondsToSelector:@selector(createArgsCodec)]) {
    NSObject<FlutterMessageCodec>* codec = [factory createArgsCodec];
    if (codec != nil && args[@"params"] != nil) {
      FlutterStandardTypedData* paramsData = args[@"params"];
      params = [codec decode:paramsData.data];
    }
  }

  NSObject<FlutterPlatformView>* embedded_view = [factory createWithFrame:CGRectZero
                                                           viewIdentifier:viewId
                                                                arguments:params];
  // Set a unique view identifier, so the platform view can be identified in unit tests.
  [embedded_view view].accessibilityIdentifier =
      [NSString stringWithFormat:@"platform_view[%ld]", viewId];
  views_[viewId] = fml::scoped_nsobject<NSObject<FlutterPlatformView>>([embedded_view retain]);

  FlutterTouchInterceptingView* touch_interceptor = [[[FlutterTouchInterceptingView alloc]
                  initWithEmbeddedView:embedded_view.view
               platformViewsController:GetWeakPtr()
      gestureRecognizersBlockingPolicy:gesture_recognizers_blocking_policies[viewType]]
      autorelease];

  touch_interceptors_[viewId] =
      fml::scoped_nsobject<FlutterTouchInterceptingView>([touch_interceptor retain]);

  ChildClippingView* clipping_view =
      [[[ChildClippingView alloc] initWithFrame:CGRectZero] autorelease];
  [clipping_view addSubview:touch_interceptor];
  root_views_[viewId] = fml::scoped_nsobject<UIView>([clipping_view retain]);

  result(nil);
}

void FlutterPlatformViewsController::OnDispose(FlutterMethodCall* call, FlutterResult& result) {
  NSNumber* arg = [call arguments];
  int64_t viewId = [arg longLongValue];

  if (views_.count(viewId) == 0) {
    result([FlutterError errorWithCode:@"unknown_view"
                               message:@"trying to dispose an unknown"
                               details:[NSString stringWithFormat:@"view id: '%lld'", viewId]]);
    return;
  }
  // We wait for next submitFrame to dispose views.
  views_to_dispose_.insert(viewId);
  result(nil);
}

void FlutterPlatformViewsController::OnAcceptGesture(FlutterMethodCall* call,
                                                     FlutterResult& result) {
  NSDictionary<NSString*, id>* args = [call arguments];
  int64_t viewId = [args[@"id"] longLongValue];

  if (views_.count(viewId) == 0) {
    result([FlutterError errorWithCode:@"unknown_view"
                               message:@"trying to set gesture state for an unknown view"
                               details:[NSString stringWithFormat:@"view id: '%lld'", viewId]]);
    return;
  }

  FlutterTouchInterceptingView* view = touch_interceptors_[viewId].get();
  [view releaseGesture];

  result(nil);
}

void FlutterPlatformViewsController::OnRejectGesture(FlutterMethodCall* call,
                                                     FlutterResult& result) {
  NSDictionary<NSString*, id>* args = [call arguments];
  int64_t viewId = [args[@"id"] longLongValue];

  if (views_.count(viewId) == 0) {
    result([FlutterError errorWithCode:@"unknown_view"
                               message:@"trying to set gesture state for an unknown view"
                               details:[NSString stringWithFormat:@"view id: '%lld'", viewId]]);
    return;
  }

  FlutterTouchInterceptingView* view = touch_interceptors_[viewId].get();
  [view blockGesture];

  result(nil);
}

void FlutterPlatformViewsController::RegisterViewFactory(
    NSObject<FlutterPlatformViewFactory>* factory,
    NSString* factoryId,
    FlutterPlatformViewGestureRecognizersBlockingPolicy gestureRecognizerBlockingPolicy) {
  std::string idString([factoryId UTF8String]);
  FML_CHECK(factories_.count(idString) == 0);
  factories_[idString] =
      fml::scoped_nsobject<NSObject<FlutterPlatformViewFactory>>([factory retain]);
  gesture_recognizers_blocking_policies[idString] = gestureRecognizerBlockingPolicy;
}

void FlutterPlatformViewsController::BeginFrame(SkISize frame_size) {
  ResetFrameState();
  frame_size_ = frame_size;
}

void FlutterPlatformViewsController::CancelFrame() {
  ResetFrameState();
}

// TODO(cyanglaz): https://github.com/flutter/flutter/issues/56474
// Make this method check if there are pending view operations instead.
// Also rename it to `HasPendingViewOperations`.
bool FlutterPlatformViewsController::HasPlatformViewThisOrNextFrame() {
  return composition_order_.size() > 0 || active_composition_order_.size() > 0;
}

const int FlutterPlatformViewsController::kDefaultMergedLeaseDuration;

PostPrerollResult FlutterPlatformViewsController::PostPrerollAction(
    fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) {
  // TODO(cyanglaz): https://github.com/flutter/flutter/issues/56474
  // Rename `has_platform_view` to `view_mutated` when the above issue is resolved.
  if (!HasPlatformViewThisOrNextFrame()) {
    return PostPrerollResult::kSuccess;
  }
  if (!raster_thread_merger->IsMerged()) {
    // The raster thread merger may be disabled if the rasterizer is being
    // created or teared down.
    //
    // In such cases, the current frame is dropped, and a new frame is attempted
    // with the same layer tree.
    //
    // Eventually, the frame is submitted once this method returns `kSuccess`.
    // At that point, the raster tasks are handled on the platform thread.
    raster_thread_merger->MergeWithLease(kDefaultMergedLeaseDuration);
    CancelFrame();
    return PostPrerollResult::kSkipAndRetryFrame;
  }
  // If the post preroll action is successful, we will display platform views in the current frame.
  // In order to sync the rendering of the platform views (quartz) with skia's rendering,
  // We need to begin an explicit CATransaction. This transaction needs to be submitted
  // after the current frame is submitted.
  BeginCATransaction();
  raster_thread_merger->ExtendLeaseTo(kDefaultMergedLeaseDuration);
  return PostPrerollResult::kSuccess;
}

void FlutterPlatformViewsController::PrerollCompositeEmbeddedView(
    int view_id,
    std::unique_ptr<EmbeddedViewParams> params) {
  // All the CATransactions should be committed by the end of the last frame,
  // so catransaction_added_ must be false.
  FML_DCHECK(!catransaction_added_);
  picture_recorders_[view_id] = std::make_unique<SkPictureRecorder>();

  auto rtree_factory = RTreeFactory();
  platform_view_rtrees_[view_id] = rtree_factory.getInstance();
  picture_recorders_[view_id]->beginRecording(SkRect::Make(frame_size_), &rtree_factory);

  composition_order_.push_back(view_id);

  if (current_composition_params_.count(view_id) == 1 &&
      current_composition_params_[view_id] == *params.get()) {
    // Do nothing if the params didn't change.
    return;
  }
  current_composition_params_[view_id] = EmbeddedViewParams(*params.get());
  views_to_recomposite_.insert(view_id);
}

NSObject<FlutterPlatformView>* FlutterPlatformViewsController::GetPlatformViewByID(int view_id) {
  if (views_.empty()) {
    return nil;
  }
  return views_[view_id].get();
}

std::vector<SkCanvas*> FlutterPlatformViewsController::GetCurrentCanvases() {
  std::vector<SkCanvas*> canvases;
  for (size_t i = 0; i < composition_order_.size(); i++) {
    int64_t view_id = composition_order_[i];
    canvases.push_back(picture_recorders_[view_id]->getRecordingCanvas());
  }
  return canvases;
}

int FlutterPlatformViewsController::CountClips(const MutatorsStack& mutators_stack) {
  std::vector<std::shared_ptr<Mutator>>::const_reverse_iterator iter = mutators_stack.Bottom();
  int clipCount = 0;
  while (iter != mutators_stack.Top()) {
    if ((*iter)->IsClipType()) {
      clipCount++;
    }
    ++iter;
  }
  return clipCount;
}

void FlutterPlatformViewsController::ApplyMutators(const MutatorsStack& mutators_stack,
                                                   UIView* embedded_view) {
  if (flutter_view_ == nullptr) {
    return;
  }
  FML_DCHECK(CATransform3DEqualToTransform(embedded_view.layer.transform, CATransform3DIdentity));
  ResetAnchor(embedded_view.layer);
  ChildClippingView* clipView = (ChildClippingView*)embedded_view.superview;

  // The UIKit frame is set based on the logical resolution instead of physical.
  // (https://developer.apple.com/library/archive/documentation/DeviceInformation/Reference/iOSDeviceCompatibility/Displays/Displays.html).
  // However, flow is based on the physical resolution. For example, 1000 pixels in flow equals
  // 500 points in UIKit. And until this point, we did all the calculation based on the flow
  // resolution. So we need to scale down to match UIKit's logical resolution.
  CGFloat screenScale = [UIScreen mainScreen].scale;
  CATransform3D finalTransform = CATransform3DMakeScale(1 / screenScale, 1 / screenScale, 1);

  // Mask view needs to be full screen because we might draw platform view pixels outside of the
  // `ChildClippingView`. Since the mask view's frame will be based on the `clipView`'s coordinate
  // system, we need to convert the flutter_view's frame to the clipView's coordinate system. The
  // mask view is not displayed on the screen.
  CGRect maskViewFrame = [flutter_view_ convertRect:flutter_view_.get().frame toView:clipView];
  FlutterClippingMaskView* maskView =
      [[[FlutterClippingMaskView alloc] initWithFrame:maskViewFrame] autorelease];
  auto iter = mutators_stack.Begin();
  while (iter != mutators_stack.End()) {
    switch ((*iter)->GetType()) {
      case transform: {
        CATransform3D transform = GetCATransform3DFromSkMatrix((*iter)->GetMatrix());
        finalTransform = CATransform3DConcat(transform, finalTransform);
        break;
      }
      case clip_rect:
        [maskView clipRect:(*iter)->GetRect() matrix:finalTransform];
        break;
      case clip_rrect:
        [maskView clipRRect:(*iter)->GetRRect() matrix:finalTransform];
        break;
      case clip_path:
        [maskView clipPath:(*iter)->GetPath() matrix:finalTransform];
        break;
      case opacity:
        embedded_view.alpha = (*iter)->GetAlphaFloat() * embedded_view.alpha;
        break;
    }
    ++iter;
  }
  // Reverse the offset of the clipView.
  // The clipView's frame includes the final translate of the final transform matrix.
  // So we need to revese this translate so the platform view can layout at the correct offset.
  //
  // Note that we don't apply this transform matrix the clippings because clippings happen on the
  // mask view, whose origin is alwasy (0,0) to the flutter_view.
  CATransform3D reverseTranslate =
      CATransform3DMakeTranslation(-clipView.frame.origin.x, -clipView.frame.origin.y, 0);
  embedded_view.layer.transform = CATransform3DConcat(finalTransform, reverseTranslate);
  clipView.maskView = maskView;
}

void FlutterPlatformViewsController::CompositeWithParams(int view_id,
                                                         const EmbeddedViewParams& params) {
  CGRect frame = CGRectMake(0, 0, params.sizePoints().width(), params.sizePoints().height());
  UIView* touchInterceptor = touch_interceptors_[view_id].get();
  touchInterceptor.layer.transform = CATransform3DIdentity;
  touchInterceptor.frame = frame;
  touchInterceptor.alpha = 1;

  const MutatorsStack& mutatorStack = params.mutatorsStack();
  UIView* clippingView = root_views_[view_id].get();
  // The frame of the clipping view should be the final bounding rect.
  // Because the translate matrix in the Mutator Stack also includes the offset,
  // when we apply the transforms matrix in |ApplyMutators|, we need
  // to remember to do a reverse translate.
  const SkRect& rect = params.finalBoundingRect();
  CGFloat screenScale = [UIScreen mainScreen].scale;
  clippingView.frame = CGRectMake(rect.x() / screenScale, rect.y() / screenScale,
                                  rect.width() / screenScale, rect.height() / screenScale);
  ApplyMutators(mutatorStack, touchInterceptor);
}

SkCanvas* FlutterPlatformViewsController::CompositeEmbeddedView(int view_id) {
  // Any UIKit related code has to run on main thread.
  FML_DCHECK([[NSThread currentThread] isMainThread]);

  // Do nothing if the view doesn't need to be composited.
  if (views_to_recomposite_.count(view_id) == 0) {
    return picture_recorders_[view_id]->getRecordingCanvas();
  }
  CompositeWithParams(view_id, current_composition_params_[view_id]);
  views_to_recomposite_.erase(view_id);
  return picture_recorders_[view_id]->getRecordingCanvas();
}

void FlutterPlatformViewsController::Reset() {
  UIView* flutter_view = flutter_view_.get();
  for (UIView* sub_view in [flutter_view subviews]) {
    [sub_view removeFromSuperview];
  }
  root_views_.clear();
  touch_interceptors_.clear();
  views_.clear();
  composition_order_.clear();
  active_composition_order_.clear();
  picture_recorders_.clear();
  platform_view_rtrees_.clear();
  current_composition_params_.clear();
  clip_count_.clear();
  views_to_recomposite_.clear();
  layer_pool_->RecycleLayers();
}

SkRect FlutterPlatformViewsController::GetPlatformViewRect(int view_id) {
  UIView* platform_view = [views_[view_id].get() view];
  UIScreen* screen = [UIScreen mainScreen];
  CGRect platform_view_cgrect = [platform_view convertRect:platform_view.bounds
                                                    toView:flutter_view_];
  return SkRect::MakeXYWH(platform_view_cgrect.origin.x * screen.scale,    //
                          platform_view_cgrect.origin.y * screen.scale,    //
                          platform_view_cgrect.size.width * screen.scale,  //
                          platform_view_cgrect.size.height * screen.scale  //
  );
}

bool FlutterPlatformViewsController::SubmitFrame(
    GrDirectContext* gr_context,
    std::shared_ptr<IOSContext> ios_context,
    std::unique_ptr<SurfaceFrame> frame,
    const std::shared_ptr<fml::SyncSwitch>& gpu_disable_sync_switch) {
  bool result = false;
  gpu_disable_sync_switch->Execute(
      fml::SyncSwitch::Handlers().SetIfTrue([&] { result = false; }).SetIfFalse([&] {
        result = SubmitFrameGpuSafe(gr_context, ios_context, std::move(frame));
      }));
  return result;
}

bool FlutterPlatformViewsController::SubmitFrameGpuSafe(GrDirectContext* gr_context,
                                                        std::shared_ptr<IOSContext> ios_context,
                                                        std::unique_ptr<SurfaceFrame> frame) {
  // Any UIKit related code has to run on main thread.
  FML_DCHECK([[NSThread currentThread] isMainThread]);
  if (flutter_view_ == nullptr) {
    return frame->Submit();
  }

  DisposeViews();

  SkCanvas* background_canvas = frame->SkiaCanvas();

  // Resolve all pending GPU operations before allocating a new surface.
  background_canvas->flush();
  // Clipping the background canvas before drawing the picture recorders requires to
  // save and restore the clip context.
  SkAutoCanvasRestore save(background_canvas, /*doSave=*/true);
  // Maps a platform view id to a vector of `FlutterPlatformViewLayer`.
  LayersMap platform_view_layers;

  auto did_submit = true;
  auto num_platform_views = composition_order_.size();

  for (size_t i = 0; i < num_platform_views; i++) {
    int64_t platform_view_id = composition_order_[i];
    sk_sp<RTree> rtree = platform_view_rtrees_[platform_view_id];
    sk_sp<SkPicture> picture = picture_recorders_[platform_view_id]->finishRecordingAsPicture();

    // Check if the current picture contains overlays that intersect with the
    // current platform view or any of the previous platform views.
    for (size_t j = i + 1; j > 0; j--) {
      int64_t current_platform_view_id = composition_order_[j - 1];
      SkRect platform_view_rect = GetPlatformViewRect(current_platform_view_id);
      std::list<SkRect> intersection_rects =
          rtree->searchNonOverlappingDrawnRects(platform_view_rect);
      auto allocation_size = intersection_rects.size();

      // For testing purposes, the overlay id is used to find the overlay view.
      // This is the index of the layer for the current platform view.
      auto overlay_id = platform_view_layers[current_platform_view_id].size();

      // If the max number of allocations per platform view is exceeded,
      // then join all the rects into a single one.
      //
      // TODO(egarciad): Consider making this configurable.
      // https://github.com/flutter/flutter/issues/52510
      if (allocation_size > kMaxLayerAllocations) {
        SkRect joined_rect;
        for (const SkRect& rect : intersection_rects) {
          joined_rect.join(rect);
        }
        // Replace the rects in the intersection rects list for a single rect that is
        // the union of all the rects in the list.
        intersection_rects.clear();
        intersection_rects.push_back(joined_rect);
      }
      for (SkRect& joined_rect : intersection_rects) {
        // Get the intersection rect between the current rect
        // and the platform view rect.
        joined_rect.intersect(platform_view_rect);
        // Subpixels in the platform may not align with the canvas subpixels.
        // To workaround it, round the floating point bounds and make the rect slighly larger.
        // For example, {0.3, 0.5, 3.1, 4.7} becomes {0, 0, 4, 5}.
        joined_rect.setLTRB(std::floor(joined_rect.left()), std::floor(joined_rect.top()),
                            std::ceil(joined_rect.right()), std::ceil(joined_rect.bottom()));
        // Clip the background canvas, so it doesn't contain any of the pixels drawn
        // on the overlay layer.
        background_canvas->clipRect(joined_rect, SkClipOp::kDifference);
        // Get a new host layer.
        std::shared_ptr<FlutterPlatformViewLayer> layer = GetLayer(gr_context,                //
                                                                   ios_context,               //
                                                                   picture,                   //
                                                                   joined_rect,               //
                                                                   current_platform_view_id,  //
                                                                   overlay_id                 //
        );
        did_submit &= layer->did_submit_last_frame;
        platform_view_layers[current_platform_view_id].push_back(layer);
        overlay_id++;
      }
    }
    background_canvas->drawPicture(picture);
  }
  // If a layer was allocated in the previous frame, but it's not used in the current frame,
  // then it can be removed from the scene.
  RemoveUnusedLayers();
  // Organize the layers by their z indexes.
  BringLayersIntoView(platform_view_layers);
  // Mark all layers as available, so they can be used in the next frame.
  layer_pool_->RecycleLayers();

  did_submit &= frame->Submit();

  // If the frame is submitted with embedded platform views,
  // there should be a |[CATransaction begin]| call in this frame prior to all the drawing.
  // If that case, we need to commit the transaction.
  CommitCATransactionIfNeeded();
  return did_submit;
}

void FlutterPlatformViewsController::BringLayersIntoView(LayersMap layer_map) {
  FML_DCHECK(flutter_view_);
  UIView* flutter_view = flutter_view_.get();
  auto zIndex = 0;
  // Clear the `active_composition_order_`, which will be populated down below.
  active_composition_order_.clear();
  for (size_t i = 0; i < composition_order_.size(); i++) {
    int64_t platform_view_id = composition_order_[i];
    std::vector<std::shared_ptr<FlutterPlatformViewLayer>> layers = layer_map[platform_view_id];
    UIView* platform_view_root = root_views_[platform_view_id].get();

    if (platform_view_root.superview != flutter_view) {
      [flutter_view addSubview:platform_view_root];
    } else {
      platform_view_root.layer.zPosition = zIndex++;
    }
    for (const std::shared_ptr<FlutterPlatformViewLayer>& layer : layers) {
      if ([layer->overlay_view_wrapper superview] != flutter_view) {
        [flutter_view addSubview:layer->overlay_view_wrapper];
      } else {
        layer->overlay_view_wrapper.get().layer.zPosition = zIndex++;
      }
    }
    active_composition_order_.push_back(platform_view_id);
  }
}

std::shared_ptr<FlutterPlatformViewLayer> FlutterPlatformViewsController::GetLayer(
    GrDirectContext* gr_context,
    std::shared_ptr<IOSContext> ios_context,
    sk_sp<SkPicture> picture,
    SkRect rect,
    int64_t view_id,
    int64_t overlay_id) {
  FML_DCHECK(flutter_view_);
  std::shared_ptr<FlutterPlatformViewLayer> layer = layer_pool_->GetLayer(gr_context, ios_context);

  UIView* overlay_view_wrapper = layer->overlay_view_wrapper.get();
  auto screenScale = [UIScreen mainScreen].scale;
  // Set the size of the overlay view wrapper.
  // This wrapper view masks the overlay view.
  overlay_view_wrapper.frame = CGRectMake(rect.x() / screenScale, rect.y() / screenScale,
                                          rect.width() / screenScale, rect.height() / screenScale);
  // Set a unique view identifier, so the overlay wrapper can be identified in unit tests.
  overlay_view_wrapper.accessibilityIdentifier =
      [NSString stringWithFormat:@"platform_view[%lld].overlay[%lld]", view_id, overlay_id];

  UIView* overlay_view = layer->overlay_view.get();
  // Set the size of the overlay view.
  // This size is equal to the the device screen size.
  overlay_view.frame = flutter_view_.get().bounds;

  std::unique_ptr<SurfaceFrame> frame = layer->surface->AcquireFrame(frame_size_);
  // If frame is null, AcquireFrame already printed out an error message.
  if (!frame) {
    return layer;
  }
  SkCanvas* overlay_canvas = frame->SkiaCanvas();
  overlay_canvas->clear(SK_ColorTRANSPARENT);
  // Offset the picture since its absolute position on the scene is determined
  // by the position of the overlay view.
  overlay_canvas->translate(-rect.x(), -rect.y());
  overlay_canvas->drawPicture(picture);

  layer->did_submit_last_frame = frame->Submit();
  return layer;
}

void FlutterPlatformViewsController::RemoveUnusedLayers() {
  std::vector<std::shared_ptr<FlutterPlatformViewLayer>> layers = layer_pool_->GetUnusedLayers();
  for (const std::shared_ptr<FlutterPlatformViewLayer>& layer : layers) {
    [layer->overlay_view_wrapper removeFromSuperview];
  }

  std::unordered_set<int64_t> composition_order_set;
  for (int64_t view_id : composition_order_) {
    composition_order_set.insert(view_id);
  }
  // Remove unused platform views.
  for (int64_t view_id : active_composition_order_) {
    if (composition_order_set.find(view_id) == composition_order_set.end()) {
      UIView* platform_view_root = root_views_[view_id].get();
      [platform_view_root removeFromSuperview];
    }
  }
}

void FlutterPlatformViewsController::DisposeViews() {
  if (views_to_dispose_.empty()) {
    return;
  }

  FML_DCHECK([[NSThread currentThread] isMainThread]);

  for (int64_t viewId : views_to_dispose_) {
    UIView* root_view = root_views_[viewId].get();
    [root_view removeFromSuperview];
    views_.erase(viewId);
    touch_interceptors_.erase(viewId);
    root_views_.erase(viewId);
    current_composition_params_.erase(viewId);
    clip_count_.erase(viewId);
    views_to_recomposite_.erase(viewId);
  }
  views_to_dispose_.clear();
}

void FlutterPlatformViewsController::BeginCATransaction() {
  FML_DCHECK([[NSThread currentThread] isMainThread]);
  FML_DCHECK(!catransaction_added_);
  [CATransaction begin];
  catransaction_added_ = true;
}

void FlutterPlatformViewsController::CommitCATransactionIfNeeded() {
  if (catransaction_added_) {
    FML_DCHECK([[NSThread currentThread] isMainThread]);
    [CATransaction commit];
    catransaction_added_ = false;
  }
}

void FlutterPlatformViewsController::ResetFrameState() {
  picture_recorders_.clear();
  composition_order_.clear();
}

}  // namespace flutter

// This recognizers delays touch events from being dispatched to the responder chain until it failed
// recognizing a gesture.
//
// We only fail this recognizer when asked to do so by the Flutter framework (which does so by
// invoking an acceptGesture method on the platform_views channel). And this is how we allow the
// Flutter framework to delay or prevent the embedded view from getting a touch sequence.
@interface DelayingGestureRecognizer : UIGestureRecognizer <UIGestureRecognizerDelegate>

// Indicates that if the `DelayingGestureRecognizer`'s state should be set to
// `UIGestureRecognizerStateEnded` during next `touchesEnded` call.
@property(nonatomic) bool shouldEndInNextTouchesEnded;

// Indicates that the `DelayingGestureRecognizer`'s `touchesEnded` has been invoked without
// setting the state to `UIGestureRecognizerStateEnded`.
@property(nonatomic) bool touchedEndedWithoutBlocking;

- (instancetype)initWithTarget:(id)target
                        action:(SEL)action
          forwardingRecognizer:(UIGestureRecognizer*)forwardingRecognizer;
@end

// While the DelayingGestureRecognizer is preventing touches from hitting the responder chain
// the touch events are not arriving to the FlutterView (and thus not arriving to the Flutter
// framework). We use this gesture recognizer to dispatch the events directly to the FlutterView
// while during this phase.
//
// If the Flutter framework decides to dispatch events to the embedded view, we fail the
// DelayingGestureRecognizer which sends the events up the responder chain. But since the events
// are handled by the embedded view they are not delivered to the Flutter framework in this phase
// as well. So during this phase as well the ForwardingGestureRecognizer dispatched the events
// directly to the FlutterView.
@interface ForwardingGestureRecognizer : UIGestureRecognizer <UIGestureRecognizerDelegate>
- (instancetype)initWithTarget:(id)target
       platformViewsController:
           (fml::WeakPtr<flutter::FlutterPlatformViewsController>)platformViewsController;
@end

@implementation FlutterTouchInterceptingView {
  fml::scoped_nsobject<DelayingGestureRecognizer> _delayingRecognizer;
  FlutterPlatformViewGestureRecognizersBlockingPolicy _blockingPolicy;
}
- (instancetype)initWithEmbeddedView:(UIView*)embeddedView
             platformViewsController:
                 (fml::WeakPtr<flutter::FlutterPlatformViewsController>)platformViewsController
    gestureRecognizersBlockingPolicy:
        (FlutterPlatformViewGestureRecognizersBlockingPolicy)blockingPolicy {
  self = [super initWithFrame:embeddedView.frame];
  if (self) {
    self.multipleTouchEnabled = YES;
    embeddedView.autoresizingMask =
        (UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight);

    [self addSubview:embeddedView];

    ForwardingGestureRecognizer* forwardingRecognizer = [[[ForwardingGestureRecognizer alloc]
                 initWithTarget:self
        platformViewsController:std::move(platformViewsController)] autorelease];

    _delayingRecognizer.reset([[DelayingGestureRecognizer alloc]
              initWithTarget:self
                      action:nil
        forwardingRecognizer:forwardingRecognizer]);
    _blockingPolicy = blockingPolicy;

    [self addGestureRecognizer:_delayingRecognizer.get()];
    [self addGestureRecognizer:forwardingRecognizer];
  }
  return self;
}

- (void)releaseGesture {
  _delayingRecognizer.get().state = UIGestureRecognizerStateFailed;
}

- (void)blockGesture {
  switch (_blockingPolicy) {
    case FlutterPlatformViewGestureRecognizersBlockingPolicyEager:
      // We block all other gesture recognizers immediately in this policy.
      _delayingRecognizer.get().state = UIGestureRecognizerStateEnded;
      break;
    case FlutterPlatformViewGestureRecognizersBlockingPolicyWaitUntilTouchesEnded:
      if (_delayingRecognizer.get().touchedEndedWithoutBlocking) {
        // If touchesEnded of the `DelayingGesureRecognizer` has been already invoked,
        // we want to set the state of the `DelayingGesureRecognizer` to
        // `UIGestureRecognizerStateEnded` as soon as possible.
        _delayingRecognizer.get().state = UIGestureRecognizerStateEnded;
      } else {
        // If touchesEnded of the `DelayingGesureRecognizer` has not been invoked,
        // We will set a flag to notify the `DelayingGesureRecognizer` to set the state to
        // `UIGestureRecognizerStateEnded` when touchesEnded is called.
        _delayingRecognizer.get().shouldEndInNextTouchesEnded = YES;
      }
      break;
    default:
      break;
  }
}

// We want the intercepting view to consume the touches and not pass the touches up to the parent
// view. Make the touch event method not call super will not pass the touches up to the parent view.
// Hence we overide the touch event methods and do nothing.
- (void)touchesBegan:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
}

- (void)touchesMoved:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
}

- (void)touchesCancelled:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
}

- (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {
}

@end

@implementation DelayingGestureRecognizer {
  fml::scoped_nsobject<UIGestureRecognizer> _forwardingRecognizer;
}

- (instancetype)initWithTarget:(id)target
                        action:(SEL)action
          forwardingRecognizer:(UIGestureRecognizer*)forwardingRecognizer {
  self = [super initWithTarget:target action:action];
  if (self) {
    self.delaysTouchesBegan = YES;
    self.delaysTouchesEnded = YES;
    self.delegate = self;
    self.shouldEndInNextTouchesEnded = NO;
    self.touchedEndedWithoutBlocking = NO;
    _forwardingRecognizer.reset([forwardingRecognizer retain]);
  }
  return self;
}

- (BOOL)gestureRecognizer:(UIGestureRecognizer*)gestureRecognizer
    shouldBeRequiredToFailByGestureRecognizer:(UIGestureRecognizer*)otherGestureRecognizer {
  // The forwarding gesture recognizer should always get all touch events, so it should not be
  // required to fail by any other gesture recognizer.
  return otherGestureRecognizer != _forwardingRecognizer.get() && otherGestureRecognizer != self;
}

- (BOOL)gestureRecognizer:(UIGestureRecognizer*)gestureRecognizer
    shouldRequireFailureOfGestureRecognizer:(UIGestureRecognizer*)otherGestureRecognizer {
  return otherGestureRecognizer == self;
}

- (void)touchesBegan:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
  self.touchedEndedWithoutBlocking = NO;
  [super touchesBegan:touches withEvent:event];
}

- (void)touchesEnded:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
  if (self.shouldEndInNextTouchesEnded) {
    self.state = UIGestureRecognizerStateEnded;
    self.shouldEndInNextTouchesEnded = NO;
  } else {
    self.touchedEndedWithoutBlocking = YES;
  }
  [super touchesEnded:touches withEvent:event];
}

- (void)touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event {
  self.state = UIGestureRecognizerStateFailed;
}
@end

@implementation ForwardingGestureRecognizer {
  // Weak reference to FlutterPlatformViewsController. The FlutterPlatformViewsController has
  // a reference to the FlutterViewController, where we can dispatch pointer events to.
  //
  // The lifecycle of FlutterPlatformViewsController is bind to FlutterEngine, which should always
  // outlives the FlutterViewController. And ForwardingGestureRecognizer is owned by a subview of
  // FlutterView, so the ForwardingGestureRecognizer never out lives FlutterViewController.
  // Therefore, `_platformViewsController` should never be nullptr.
  fml::WeakPtr<flutter::FlutterPlatformViewsController> _platformViewsController;
  // Counting the pointers that has started in one touch sequence.
  NSInteger _currentTouchPointersCount;
  // We can't dispatch events to the framework without this back pointer.
  // This gesture recognizer retains the `FlutterViewController` until the
  // end of a gesture sequence, that is all the touches in touchesBegan are concluded
  // with |touchesCancelled| or |touchesEnded|.
  fml::scoped_nsobject<UIViewController> _flutterViewController;
}

- (instancetype)initWithTarget:(id)target
       platformViewsController:
           (fml::WeakPtr<flutter::FlutterPlatformViewsController>)platformViewsController {
  self = [super initWithTarget:target action:nil];
  if (self) {
    self.delegate = self;
    FML_DCHECK(platformViewsController.get() != nullptr);
    _platformViewsController = std::move(platformViewsController);
    _currentTouchPointersCount = 0;
  }
  return self;
}

- (void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {
  FML_DCHECK(_currentTouchPointersCount >= 0);
  if (_currentTouchPointersCount == 0) {
    // At the start of each gesture sequence, we reset the `_flutterViewController`,
    // so that all the touch events in the same sequence are forwarded to the same
    // `_flutterViewController`.
    _flutterViewController.reset([_platformViewsController->getFlutterViewController() retain]);
  }
  [_flutterViewController.get() touchesBegan:touches withEvent:event];
  _currentTouchPointersCount += touches.count;
}

- (void)touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event {
  [_flutterViewController.get() touchesMoved:touches withEvent:event];
}

- (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {
  [_flutterViewController.get() touchesEnded:touches withEvent:event];
  _currentTouchPointersCount -= touches.count;
  // Touches in one touch sequence are sent to the touchesEnded method separately if different
  // fingers stop touching the screen at different time. So one touchesEnded method triggering does
  // not necessarially mean the touch sequence has ended. We Only set the state to
  // UIGestureRecognizerStateFailed when all the touches in the current touch sequence is ended.
  if (_currentTouchPointersCount == 0) {
    self.state = UIGestureRecognizerStateFailed;
    _flutterViewController.reset(nil);
  }
}

- (void)touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event {
  [_flutterViewController.get() touchesCancelled:touches withEvent:event];
  _currentTouchPointersCount -= touches.count;
  if (_currentTouchPointersCount == 0) {
    self.state = UIGestureRecognizerStateFailed;
    _flutterViewController.reset(nil);
  }
}

- (BOOL)gestureRecognizer:(UIGestureRecognizer*)gestureRecognizer
    shouldRecognizeSimultaneouslyWithGestureRecognizer:
        (UIGestureRecognizer*)otherGestureRecognizer {
  return YES;
}
@end