overlay_layer_pool.h

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// 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.
 
#ifndef FLUTTER_SHELL_PLATFORM_DARWIN_IOS_FRAMEWORK_SOURCE_OVERLAY_LAYER_POOL_H_
#define FLUTTER_SHELL_PLATFORM_DARWIN_IOS_FRAMEWORK_SOURCE_OVERLAY_LAYER_POOL_H_
 
#include <Metal/Metal.h>
#include <memory>
 
#import <UIKit/UIKit.h>
 
#include "flow/surface.h"
#include "fml/platform/darwin/scoped_nsobject.h"
 
#import "flutter/shell/platform/darwin/ios/ios_context.h"
 
namespace flutter {
 
class IOSSurface;
 
/// @brief State holder for a Flutter overlay layer.
struct OverlayLayer {
  OverlayLayer(const fml::scoped_nsobject<UIView>& overlay_view,
               const fml::scoped_nsobject<UIView>& overlay_view_wrapper,
               std::unique_ptr<IOSSurface> ios_surface,
               std::unique_ptr<Surface> surface);
 
  ~OverlayLayer() = default;
 
  fml::scoped_nsobject<UIView> overlay_view;
  fml::scoped_nsobject<UIView> overlay_view_wrapper;
  std::unique_ptr<IOSSurface> ios_surface;
  std::unique_ptr<Surface> surface;
 
  // Whether a frame for this layer was submitted.
  bool did_submit_last_frame;
 
  // The GrContext that is currently used by the overlay surfaces.
  // We track this to know when the GrContext for the Flutter app has changed
  // so we can update the overlay with the new context.
  GrDirectContext* gr_context;
 
  void UpdateViewState(UIView* flutter_view, SkRect rect, int64_t view_id, int64_t overlay_id);
};
 
/// @brief Storage for Overlay layers across frames.
///
/// Note: this class does not synchronize access to its layers or any layer removal. As it
/// is currently used, layers must be created on the platform thread but other methods of
/// it are called on the raster thread. This is safe as overlay layers are only ever added
/// while the raster thread is latched.
class OverlayLayerPool {
 public:
  OverlayLayerPool() = default;
 
  ~OverlayLayerPool() = default;
 
  /// @brief Gets a layer from the pool if available.
  ///
  /// The layer is marked as used until [RecycleLayers] is called.
  std::shared_ptr<OverlayLayer> GetNextLayer();
 
  /// @brief Create a new overlay layer.
  ///
  /// This method can only be called on the Platform thread.
  void CreateLayer(GrDirectContext* gr_context,
                   const std::shared_ptr<IOSContext>& ios_context,
                   MTLPixelFormat pixel_format);
 
  /// @brief Removes unused layers from the pool. Returns the unused layers.
  std::vector<std::shared_ptr<OverlayLayer>> RemoveUnusedLayers();
 
  /// @brief Marks the layers in the pool as available for reuse.
  void RecycleLayers();
 
  /// @brief The count of layers currently in the pool.
  size_t size() const;
 
 private:
  OverlayLayerPool(const OverlayLayerPool&) = delete;
  OverlayLayerPool& operator=(const OverlayLayerPool&) = delete;
 
  // The index of the entry in the layers_ vector that determines the beginning of the unused
  // layers. For example, consider the following vector:
  //  _____
  //  | 0 |
  /// |---|
  /// | 1 | <-- available_layer_index_
  /// |---|
  /// | 2 |
  /// |---|
  ///
  /// This indicates that entries starting from 1 can be reused meanwhile the entry at position 0
  /// cannot be reused.
  size_t available_layer_index_ = 0;
  std::vector<std::shared_ptr<OverlayLayer>> layers_;
};
 
}  // namespace flutter
 
#endif  // FLUTTER_SHELL_PLATFORM_DARWIN_IOS_FRAMEWORK_SOURCE_OVERLAY_LAYER_POOL_H_