flutter_flutter/shell/common/renderer_context_manager.h

// 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_COMMON_RENDERER_CONTEXT_MANAGER_H_
#define FLUTTER_SHELL_COMMON_RENDERER_CONTEXT_MANAGER_H_

#include <functional>
#include <memory>
#include <vector>

#include "flutter/fml/logging.h"
#include "flutter/fml/macros.h"

namespace flutter {

//------------------------------------------------------------------------------
/// An abstract class represents a renderer context
///
/// The subclass should wrap a "Context" object inside this class. For example,
/// in iOS while using GL rendering surface, the subclass should wrap an
/// |EAGLContext|.
class RendererContext {
 public:
  //------------------------------------------------------------------------------
  /// Implement this to set the context wrapped by this |RendererContext| object
  /// to the current context.
  virtual bool SetCurrent() = 0;

  //------------------------------------------------------------------------------
  /// Implement this to remove the context wrapped by this |RendererContext|
  /// object from current context;
  virtual void RemoveCurrent() = 0;

  RendererContext();

  virtual ~RendererContext();

  FML_DISALLOW_COPY_AND_ASSIGN(RendererContext);
};

//------------------------------------------------------------------------------
/// Manages the renderer context.
///
/// Initially, the |RendererContextManager| doesn't know any context that is set
/// by other programs (e.g. a plugin). To make sure not to pollute the other
/// context, use `MakeCurrent` to set other context, so |RendererContextManager|
/// has a reference of the other context. Ideally, this process has to be done
/// everytime before a context used by Flutter is set, if the current context at
/// the moment is not null or used by Flutter.
class RendererContextManager {
 public:
  //------------------------------------------------------------------------------
  /// Switches the renderer context to the a context that is passed in the
  /// constructor.
  ///
  /// In destruction, it should reset the current context back to what was
  /// before the construction of this switch.
  ///
  class RendererContextSwitch {
   public:
    //----------------------------------------------------------------------------
    /// Constructs a |RendererContextSwitch|.
    ///
    /// @param  manager A reference to the manager.
    /// @param  context The context that is going to be set as the current
    /// context.
    RendererContextSwitch(RendererContextManager& manager,
                          std::unique_ptr<RendererContext> context);

    ~RendererContextSwitch();

    //----------------------------------------------------------------------------
    // Returns true if the context switching was successful.
    bool GetResult();

   private:
    RendererContextManager& manager_;
    bool result_;

    FML_DISALLOW_COPY_AND_ASSIGN(RendererContextSwitch);
  };

  RendererContextManager(std::unique_ptr<RendererContext> context,
                         std::unique_ptr<RendererContext> resource_context);

  ~RendererContextManager();

  //----------------------------------------------------------------------------
  /// @brief      Make the `context` to be the current context. It can be used
  /// to set a context set by other programs to be the current context in
  /// |RendererContextManager|. Which make sure Flutter doesn't pollute other
  /// contexts.
  ///
  /// @return     A `RendererContextSwitch` which ensures the `context` is the
  /// current context.
  RendererContextSwitch MakeCurrent(std::unique_ptr<RendererContext> context);

  //----------------------------------------------------------------------------
  /// @brief      Make the context Flutter uses on the raster thread for
  /// onscreen rendering to be the current context.
  ///
  /// @return     A `RendererContextSwitch` which ensures the current context is
  /// the `context` that used in the constructor.
  RendererContextSwitch FlutterMakeCurrent();

  //----------------------------------------------------------------------------
  /// @brief      Make the context Flutter uses for performing texture upload on
  /// the IO thread to be the current context.
  ///
  /// @return     A `RendererContextSwitch` which ensures the current context is
  /// the `resource_context` that used in the constructor.
  RendererContextSwitch FlutterResourceMakeCurrent();

 private:
  std::unique_ptr<RendererContext> context_;
  std::unique_ptr<RendererContext> resource_context_;

  std::unique_ptr<RendererContext> current_;

  std::vector<std::unique_ptr<RendererContext>> stored_;

  bool PushContext(std::unique_ptr<RendererContext> context);
  void PopContext();

  FML_DISALLOW_COPY_AND_ASSIGN(RendererContextManager);
};

}  // namespace flutter

#endif