src/embedder/software_surface_producer.h

// Copyright 2022 The Fuchsia 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 SRC_EMBEDDER_SOFTWARE_SURFACE_PRODUCER_H_
#define SRC_EMBEDDER_SOFTWARE_SURFACE_PRODUCER_H_

#include <fuchsia/sysmem/cpp/fidl.h>
#include <fuchsia/ui/composition/cpp/fidl.h>
#include <lib/ui/scenic/cpp/resources.h>
#include <lib/ui/scenic/cpp/session.h>

#include <unordered_map>

#include "src/embedder/software_surface.h"

namespace embedder {

/// Factory for `SoftwareSurface`s that can recycle surfaces
/// and maintains older surfaces.
class SoftwareSurfaceProducer final {
 public:
  // Only keep 12 surfaces at a time.
  static constexpr int kMaxSurfaces = 12;
  // If a surface doesn't get used for 3 or more generations, we discard it.
  static constexpr int kMaxSurfaceAge = 3;

  explicit SoftwareSurfaceProducer();
  ~SoftwareSurfaceProducer();
  SoftwareSurfaceProducer(const SoftwareSurfaceProducer&) = delete;
  SoftwareSurfaceProducer& operator=(const SoftwareSurfaceProducer&) = delete;

  bool IsValid() const;

  std::unique_ptr<SoftwareSurface> ProduceOffscreenSurface(const Size size);

  std::unique_ptr<SoftwareSurface> ProduceSurface(const Size size);

  void SubmitSurfaces(std::vector<std::unique_ptr<SoftwareSurface>> surfaces);

 private:
  std::unique_ptr<SoftwareSurface> CreateSurface(const Size size);
  void SubmitSurface(std::unique_ptr<SoftwareSurface> surface);
  void RecycleSurface(std::unique_ptr<SoftwareSurface> surface);
  void RecyclePendingSurface(uintptr_t surface_key);

  /// Increments the age of all surfaces, and removes any that are past
  /// `kMaxSurfaceAge`.
  void AgeAndCollectOldBuffers();

  /// The allocator for memory in Flatland.
  ///
  /// Required to allocate a surface for Flatland. See
  /// notes in
  /// https://fuchsia.dev/fuchsia-src/concepts/ui/scenic/flatland?hl=en#design.
  fuchsia::ui::composition::AllocatorPtr flatland_allocator_;

  /// Allocator for memory from sysmem.
  ///
  /// Memory for graphics surfaces on Fuchsia must come from sysmem.
  ///
  /// For more details on how sysmem works and how to interact with
  /// sysmem, see
  /// https://fuchsia.dev/fuchsia-src/development/graphics/sysmem/concepts/sysmem.
  fuchsia::sysmem::AllocatorSyncPtr sysmem_allocator_;

  /// These surfaces are available for re-use.
  std::vector<std::unique_ptr<SoftwareSurface>> available_surfaces_;
  /// These surfaces have been written to, but Scenic is not finished reading
  /// from them yet.
  std::unordered_map<uintptr_t, std::unique_ptr<SoftwareSurface>> pending_surfaces_;

  /// True if the `SoftwareSurfaceProducer` is in a valid state to produce
  /// surfaces, false otherwise.
  ///
  /// An invalid `SoftwareSurfaceProducer` is unrecoverable.
  bool valid_ = false;

  // TODO(akbiggs): Add tracing once we figure out how to use the embedder's
  // tracing utilities.
};

}  // namespace embedder

#endif  // SRC_EMBEDDER_SOFTWARE_SURFACE_PRODUCER_H_