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//
// Copyright 2016 The ANGLE Project Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// Observer:
// Implements the Observer pattern for sending state change notifications
// from Subject objects to dependent Observer objects.
//
// See design document:
// https://docs.google.com/document/d/15Edfotqg6_l1skTEL8ADQudF_oIdNa7i8Po43k6jMd4/
#ifndef LIBANGLE_OBSERVER_H_
#define LIBANGLE_OBSERVER_H_
#include "common/FastVector.h"
#include "common/angleutils.h"
namespace angle
{
template <typename HaystackT, typename NeedleT>
bool IsInContainer(const HaystackT &haystack, const NeedleT &needle)
{
return std::find(haystack.begin(), haystack.end(), needle) != haystack.end();
}
using SubjectIndex = size_t;
// Messages are used to distinguish different Subject events that get sent to a single Observer.
// It could be possible to improve the handling by using different callback functions instead
// of a single handler function. But in some cases we want to share a single binding between
// Observer and Subject and handle different types of events.
enum class SubjectMessage
{
// Used by gl::VertexArray to notify gl::Context of a gl::Buffer binding count change. Triggers
// a validation cache update.
BindingChanged,
// Only the contents (pixels, bytes, etc) changed in this Subject. Distinct from the object
// storage.
ContentsChanged,
// Sent by gl::Sampler, gl::Texture, gl::Framebuffer and others to notifiy gl::Context. This
// flag indicates to call syncState before next use.
DirtyBitsFlagged,
// Generic state change message. Used in multiple places for different purposes.
SubjectChanged,
// Indicates a bound gl::Buffer is now mapped or unmapped. Passed from gl::Buffer, through
// gl::VertexArray, into gl::Context. Used to track validation.
SubjectMapped,
SubjectUnmapped,
};
// The observing class inherits from this interface class.
class ObserverInterface
{
public:
virtual ~ObserverInterface();
virtual void onSubjectStateChange(SubjectIndex index, SubjectMessage message) = 0;
};
class ObserverBindingBase
{
public:
ObserverBindingBase(ObserverInterface *observer, SubjectIndex subjectIndex)
: mObserver(observer), mIndex(subjectIndex)
{}
virtual ~ObserverBindingBase() {}
ObserverInterface *getObserver() const { return mObserver; }
SubjectIndex getSubjectIndex() const { return mIndex; }
virtual void onSubjectReset() {}
private:
ObserverInterface *mObserver;
SubjectIndex mIndex;
};
// Maintains a list of observer bindings. Sends update messages to the observer.
class Subject : NonCopyable
{
public:
Subject();
virtual ~Subject();
void onStateChange(SubjectMessage message) const;
bool hasObservers() const;
void resetObservers();
ANGLE_INLINE void addObserver(ObserverBindingBase *observer)
{
ASSERT(!IsInContainer(mObservers, observer));
mObservers.push_back(observer);
}
ANGLE_INLINE void removeObserver(ObserverBindingBase *observer)
{
ASSERT(IsInContainer(mObservers, observer));
mObservers.remove_and_permute(observer);
}
private:
// Keep a short list of observers so we can allocate/free them quickly. But since we support
// unlimited bindings, have a spill-over list of that uses dynamic allocation.
static constexpr size_t kMaxFixedObservers = 8;
angle::FastVector<ObserverBindingBase *, kMaxFixedObservers> mObservers;
};
// Keeps a binding between a Subject and Observer, with a specific subject index.
class ObserverBinding final : public ObserverBindingBase
{
public:
ObserverBinding(ObserverInterface *observer, SubjectIndex index);
~ObserverBinding() override;
ObserverBinding(const ObserverBinding &other);
ObserverBinding &operator=(const ObserverBinding &other);
void bind(Subject *subject);
ANGLE_INLINE void reset() { bind(nullptr); }
void onStateChange(SubjectMessage message) const;
void onSubjectReset() override;
ANGLE_INLINE const Subject *getSubject() const { return mSubject; }
ANGLE_INLINE void assignSubject(Subject *subject) { mSubject = subject; }
private:
Subject *mSubject;
};
} // namespace angle
#endif // LIBANGLE_OBSERVER_H_
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