Move Codec2-related code from hardware/google/av

Test: None
Bug: 112362730
Change-Id: Ie2f8ff431d65c40333f267ab9877d47089adeea4
diff --git a/media/codec2/include/C2Buffer.h b/media/codec2/include/C2Buffer.h
new file mode 100644
index 0000000..2997f6e
--- /dev/null
+++ b/media/codec2/include/C2Buffer.h
@@ -0,0 +1,2305 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef C2BUFFER_H_
+#define C2BUFFER_H_
+
+#include <C2.h>
+#include <C2BufferBase.h>
+#include <C2Param.h> // for C2Info
+
+#include <memory>
+#include <vector>
+
+#ifdef __ANDROID__
+#include <android-C2Buffer.h>
+#else
+
+typedef void* C2Handle;
+
+#endif
+
+/// \defgroup buffer Buffers
+/// @{
+
+/// \defgroup buffer_sync Synchronization
+/// @{
+
+/**
+ * Synchronization is accomplished using event and fence objects.
+ *
+ * These are cross-process extensions of promise/future infrastructure.
+ * Events are analogous to std::promise<void>, whereas fences are to std::shared_future<void>.
+ *
+ * Fences and events are shareable/copyable.
+ *
+ * Fences are used in two scenarios, and all copied instances refer to the same event.
+ * \todo do events need to be copyable or should they be unique?
+ *
+ * acquire sync fence object: signaled when it is safe for the component or client to access
+ * (the contents of) an object.
+ *
+ * release sync fence object: \todo
+ *
+ * Fences can be backed by hardware. Hardware fences are guaranteed to signal NO MATTER WHAT within
+ * a short (platform specific) amount of time; this guarantee is usually less than 15 msecs.
+ */
+
+/**
+ * Fence object used by components and the framework.
+ *
+ * Implements the waiting for an event, analogous to a 'future'.
+ *
+ * To be implemented by vendors if using HW fences.
+ */
+class C2Fence {
+public:
+    /**
+     * Waits for a fence to be signaled with a timeout.
+     *
+     * \todo a mechanism to cancel a wait - for now the only way to do this is to abandon the
+     * event, but fences are shared so canceling a wait will cancel all waits.
+     *
+     * \param timeoutNs           the maximum time to wait in nsecs
+     *
+     * \retval C2_OK            the fence has been signaled
+     * \retval C2_TIMED_OUT     the fence has not been signaled within the timeout
+     * \retval C2_BAD_STATE     the fence has been abandoned without being signaled (it will never
+     *                          be signaled)
+     * \retval C2_REFUSED       no permission to wait for the fence (unexpected - system)
+     * \retval C2_CORRUPTED     some unknown error prevented waiting for the fence (unexpected)
+     */
+    c2_status_t wait(c2_nsecs_t timeoutNs);
+
+    /**
+     * Used to check if this fence is valid (if there is a chance for it to be signaled.)
+     * A fence becomes invalid if the controling event is destroyed without it signaling the fence.
+     *
+     * \return whether this fence is valid
+     */
+    bool valid() const;
+
+    /**
+     * Used to check if this fence has been signaled (is ready).
+     *
+     * \return whether this fence has been signaled
+     */
+    bool ready() const;
+
+    /**
+     * Returns a file descriptor that can be used to wait for this fence in a select system call.
+     * \note The returned file descriptor, if valid, must be closed by the caller.
+     *
+     * This can be used in e.g. poll() system calls. This file becomes readable (POLLIN) when the
+     * fence is signaled, and bad (POLLERR) if the fence is abandoned.
+     *
+     * \return a file descriptor representing this fence (with ownership), or -1 if the fence
+     * has already been signaled (\todo or abandoned).
+     *
+     * \todo this must be compatible with fences used by gralloc
+     */
+    int fd() const;
+
+    /**
+     * Returns whether this fence is a hardware-backed fence.
+     * \return whether this is a hardware fence
+     */
+    bool isHW() const;
+
+    /**
+     * Null-fence. A fence that has fired.
+     */
+    constexpr C2Fence() : mImpl(nullptr) { }
+
+private:
+    class Impl;
+    std::shared_ptr<Impl> mImpl;
+    C2Fence(std::shared_ptr<Impl> impl);
+    friend struct _C2FenceFactory;
+};
+
+/**
+ * Event object used by components and the framework.
+ *
+ * Implements the signaling of an event, analogous to a 'promise'.
+ *
+ * Hardware backed events do not go through this object, and must be exposed directly as fences
+ * by vendors.
+ */
+class C2Event {
+public:
+    /**
+     * Returns a fence for this event.
+     */
+    C2Fence fence() const;
+
+    /**
+     * Signals (all) associated fence(s).
+     * This has no effect no effect if the event was already signaled or abandoned.
+     *
+     * \retval C2_OK            the fence(s) were successfully signaled
+     * \retval C2_BAD_STATE     the fence(s) have already been abandoned or merged (caller error)
+     * \retval C2_DUPLICATE     the fence(s) have already been signaled (caller error)
+     * \retval C2_REFUSED       no permission to signal the fence (unexpected - system)
+     * \retval C2_CORRUPTED     some unknown error prevented signaling the fence(s) (unexpected)
+     */
+    c2_status_t fire();
+
+    /**
+     * Trigger this event from the merging of the supplied fences. This means that it will be
+     * abandoned if any of these fences have been abandoned, and it will be fired if all of these
+     * fences have been signaled.
+     *
+     * \retval C2_OK            the merging was successfully done
+     * \retval C2_NO_MEMORY     not enough memory to perform the merging
+     * \retval C2_DUPLICATE     the fence have already been merged (caller error)
+     * \retval C2_BAD_STATE     the fence have already been signaled or abandoned (caller error)
+     * \retval C2_REFUSED       no permission to merge the fence (unexpected - system)
+     * \retval C2_CORRUPTED     some unknown error prevented merging the fence(s) (unexpected)
+     */
+    c2_status_t merge(std::vector<C2Fence> fences);
+
+    /**
+     * Abandons the event and any associated fence(s).
+     * \note Call this to explicitly abandon an event before it is destructed to avoid a warning.
+     *
+     * This has no effect no effect if the event was already signaled or abandoned.
+     *
+     * \retval C2_OK            the fence(s) were successfully signaled
+     * \retval C2_BAD_STATE     the fence(s) have already been signaled or merged (caller error)
+     * \retval C2_DUPLICATE     the fence(s) have already been abandoned (caller error)
+     * \retval C2_REFUSED       no permission to abandon the fence (unexpected - system)
+     * \retval C2_CORRUPTED     some unknown error prevented signaling the fence(s) (unexpected)
+     */
+    c2_status_t abandon();
+
+private:
+    class Impl;
+    std::shared_ptr<Impl> mImpl;
+};
+
+/// \addtogroup buf_internal Internal
+/// @{
+
+/**
+ * Interface for objects that encapsulate an updatable status value.
+ */
+struct _C2InnateStatus {
+    inline c2_status_t status() const { return mStatus; }
+
+protected:
+    _C2InnateStatus(c2_status_t status) : mStatus(status) { }
+
+    c2_status_t mStatus; // this status is updatable by the object
+};
+
+/// @}
+
+/**
+ * This is a utility template for objects protected by an acquire fence, so that errors during
+ * acquiring the object are propagated to the object itself.
+ */
+template<typename T>
+class C2Acquirable : public C2Fence {
+public:
+    /**
+     * Acquires the object protected by an acquire fence. Any errors during the mapping will be
+     * passed to the object.
+     *
+     * \return acquired object potentially invalidated if waiting for the fence failed.
+     */
+    T get() {
+        // TODO:
+        // wait();
+        return mT;
+    }
+
+protected:
+    C2Acquirable(c2_status_t error, C2Fence fence, T t) : C2Fence(fence), mInitialError(error), mT(t) { }
+
+private:
+    c2_status_t mInitialError;
+    T mT; // TODO: move instead of copy
+};
+
+/// @}
+
+/// \defgroup linear Linear Data Blocks
+/// @{
+
+/**************************************************************************************************
+  LINEAR ASPECTS, BLOCKS AND VIEWS
+**************************************************************************************************/
+
+/**
+ * Basic segment math support.
+ */
+struct C2Segment {
+    uint32_t offset;
+    uint32_t size;
+
+    inline constexpr C2Segment(uint32_t offset_, uint32_t size_)
+        : offset(offset_),
+          size(size_) {
+    }
+
+    inline constexpr bool isEmpty() const {
+        return size == 0;
+    }
+
+    inline constexpr bool isValid() const {
+        return offset <= ~size;
+    }
+
+    inline constexpr operator bool() const {
+        return isValid() && !isEmpty();
+    }
+
+    inline constexpr bool operator!() const {
+        return !bool(*this);
+    }
+
+    C2_ALLOW_OVERFLOW
+    inline constexpr bool contains(const C2Segment &other) const {
+        if (!isValid() || !other.isValid()) {
+            return false;
+        } else {
+            return offset <= other.offset
+                    && offset + size >= other.offset + other.size;
+        }
+    }
+
+    inline constexpr bool operator==(const C2Segment &other) const {
+        if (!isValid()) {
+            return !other.isValid();
+        } else {
+            return offset == other.offset && size == other.size;
+        }
+    }
+
+    inline constexpr bool operator!=(const C2Segment &other) const {
+        return !operator==(other);
+    }
+
+    inline constexpr bool operator>=(const C2Segment &other) const {
+        return contains(other);
+    }
+
+    inline constexpr bool operator>(const C2Segment &other) const {
+        return contains(other) && !operator==(other);
+    }
+
+    inline constexpr bool operator<=(const C2Segment &other) const {
+        return other.contains(*this);
+    }
+
+    inline constexpr bool operator<(const C2Segment &other) const {
+        return other.contains(*this) && !operator==(other);
+    }
+
+    C2_ALLOW_OVERFLOW
+    inline constexpr uint32_t end() const {
+        return offset + size;
+    }
+
+    C2_ALLOW_OVERFLOW
+    inline constexpr C2Segment intersect(const C2Segment &other) const {
+        return C2Segment(c2_max(offset, other.offset),
+                         c2_min(end(), other.end()) - c2_max(offset, other.offset));
+    }
+
+    /** clamps end to offset if it overflows */
+    inline constexpr C2Segment normalize() const {
+        return C2Segment(offset, c2_max(offset, end()) - offset);
+    }
+
+    /** clamps end to max if it overflows */
+    inline constexpr C2Segment saturate() const {
+        return C2Segment(offset, c2_min(size, ~offset));
+    }
+
+};
+
+/**
+ * Common aspect for all objects that have a linear capacity.
+ */
+class _C2LinearCapacityAspect {
+/// \name Linear capacity interface
+/// @{
+public:
+    inline constexpr uint32_t capacity() const { return mCapacity; }
+
+    inline constexpr operator C2Segment() const {
+        return C2Segment(0, mCapacity);
+    }
+
+protected:
+
+#if UINTPTR_MAX == 0xffffffff
+    static_assert(sizeof(size_t) == sizeof(uint32_t), "size_t is too big");
+#else
+    static_assert(sizeof(size_t) > sizeof(uint32_t), "size_t is too small");
+    // explicitly disable construction from size_t
+    inline explicit _C2LinearCapacityAspect(size_t capacity) = delete;
+#endif
+
+    inline explicit constexpr _C2LinearCapacityAspect(uint32_t capacity)
+      : mCapacity(capacity) { }
+
+    inline explicit constexpr _C2LinearCapacityAspect(const _C2LinearCapacityAspect *parent)
+        : mCapacity(parent == nullptr ? 0 : parent->capacity()) { }
+
+private:
+    uint32_t mCapacity;
+/// @}
+};
+
+/**
+ * Aspect for objects that have a linear range inside a linear capacity.
+ *
+ * This class is copiable.
+ */
+class _C2LinearRangeAspect : public _C2LinearCapacityAspect {
+/// \name Linear range interface
+/// @{
+public:
+    inline constexpr uint32_t offset() const { return mOffset; }
+    inline constexpr uint32_t endOffset() const { return mOffset + mSize; }
+    inline constexpr uint32_t size() const { return mSize; }
+
+    inline constexpr operator C2Segment() const {
+        return C2Segment(mOffset, mSize);
+    }
+
+private:
+    // subrange of capacity [0, capacity] & [size, size + offset]
+    inline constexpr _C2LinearRangeAspect(uint32_t capacity_, size_t offset, size_t size)
+        : _C2LinearCapacityAspect(capacity_),
+          mOffset(c2_min(offset, capacity())),
+          mSize(c2_min(size, capacity() - mOffset)) {
+    }
+
+protected:
+    // copy constructor (no error check)
+    inline constexpr _C2LinearRangeAspect(const _C2LinearRangeAspect &other)
+        : _C2LinearCapacityAspect(other.capacity()),
+          mOffset(other.offset()),
+          mSize(other.size()) {
+    }
+
+    // parent capacity range [0, capacity]
+    inline constexpr explicit _C2LinearRangeAspect(const _C2LinearCapacityAspect *parent)
+        : _C2LinearCapacityAspect(parent),
+          mOffset(0),
+          mSize(capacity()) {
+    }
+
+    // subrange of parent capacity [0, capacity] & [size, size + offset]
+    inline constexpr _C2LinearRangeAspect(const _C2LinearCapacityAspect *parent, size_t offset, size_t size)
+        : _C2LinearCapacityAspect(parent),
+          mOffset(c2_min(offset, capacity())),
+          mSize(c2_min(size, capacity() - mOffset)) {
+    }
+
+    // subsection of the parent's and [offset, offset + size] ranges
+    inline constexpr _C2LinearRangeAspect(const _C2LinearRangeAspect *parent, size_t offset, size_t size)
+        : _C2LinearCapacityAspect(parent),
+          mOffset(c2_min(c2_max(offset, parent == nullptr ? 0 : parent->offset()), capacity())),
+          mSize(std::min(c2_min(size, parent == nullptr ? 0 : parent->size()), capacity() - mOffset)) {
+    }
+
+public:
+    inline constexpr _C2LinearRangeAspect childRange(size_t offset, size_t size) const {
+        return _C2LinearRangeAspect(
+            mSize,
+            c2_min(c2_max(offset, mOffset), capacity()) - mOffset,
+            c2_min(c2_min(size, mSize), capacity() - c2_min(c2_max(offset, mOffset), capacity())));
+    }
+
+    friend class _C2EditableLinearRangeAspect;
+    // invariants 0 <= mOffset <= mOffset + mSize <= capacity()
+    uint32_t mOffset;
+    uint32_t mSize;
+/// @}
+};
+
+/**
+ * Utility class for safe range calculations using size_t-s.
+ */
+class C2LinearRange : public _C2LinearRangeAspect {
+public:
+    inline constexpr C2LinearRange(const _C2LinearCapacityAspect &parent, size_t offset, size_t size)
+        : _C2LinearRangeAspect(&parent, offset, size) { }
+
+    inline constexpr C2LinearRange(const _C2LinearRangeAspect &parent, size_t offset, size_t size)
+        : _C2LinearRangeAspect(&parent, offset, size) { }
+
+    inline constexpr C2LinearRange intersect(size_t offset, size_t size) const {
+        return C2LinearRange(*this, offset, size);
+    }
+};
+
+/**
+ * Utility class for simple and safe capacity and range construction.
+ */
+class C2LinearCapacity : public _C2LinearCapacityAspect {
+public:
+    inline constexpr explicit C2LinearCapacity(size_t capacity)
+        : _C2LinearCapacityAspect(c2_min(capacity, std::numeric_limits<uint32_t>::max())) { }
+
+    inline constexpr C2LinearRange range(size_t offset, size_t size) const {
+        return C2LinearRange(*this, offset, size);
+    }
+};
+
+/**
+ * Aspect for objects that have an editable linear range.
+ *
+ * This class is copiable.
+ */
+class _C2EditableLinearRangeAspect : public _C2LinearRangeAspect {
+    using _C2LinearRangeAspect::_C2LinearRangeAspect;
+
+public:
+/// \name Editable linear range interface
+/// @{
+
+    /**
+     * Sets the offset to |offset|, while trying to keep the end of the buffer unchanged (e.g.
+     * size will grow if offset is decreased, and may shrink if offset is increased.) Returns
+     * true if successful, which is equivalent to if 0 <= |offset| <= capacity().
+     *
+     * Note: setting offset and size will yield different result depending on the order of the
+     * operations. Always set offset first to ensure proper size.
+     */
+    inline bool setOffset(uint32_t offset) {
+        if (offset > capacity()) {
+            return false;
+        }
+
+        if (offset > mOffset + mSize) {
+            mSize = 0;
+        } else {
+            mSize = mOffset + mSize - offset;
+        }
+        mOffset = offset;
+        return true;
+    }
+
+    /**
+     * Sets the size to |size|. Returns true if successful, which is equivalent to
+     * if 0 <= |size| <= capacity() - offset().
+     *
+     * Note: setting offset and size will yield different result depending on the order of the
+     * operations. Always set offset first to ensure proper size.
+     */
+    inline bool setSize(uint32_t size) {
+        if (size > capacity() - mOffset) {
+            return false;
+        } else {
+            mSize = size;
+            return true;
+        }
+    }
+
+    /**
+     * Sets the offset to |offset| with best effort. Same as setOffset() except that offset will
+     * be clamped to the buffer capacity.
+     *
+     * Note: setting offset and size (even using best effort) will yield different result depending
+     * on the order of the operations. Always set offset first to ensure proper size.
+     */
+    inline void setOffset_be(uint32_t offset) {
+        (void)setOffset(c2_min(offset, capacity()));
+    }
+
+    /**
+     * Sets the size to |size| with best effort. Same as setSize() except that the selected region
+     * will be clamped to the buffer capacity (e.g. size is clamped to [0, capacity() - offset()]).
+     *
+     * Note: setting offset and size (even using best effort) will yield different result depending
+     * on the order of the operations. Always set offset first to ensure proper size.
+     */
+    inline void setSize_be(uint32_t size) {
+        mSize = c2_min(size, capacity() - mOffset);
+    }
+/// @}
+};
+
+/**************************************************************************************************
+  ALLOCATIONS
+**************************************************************************************************/
+
+/// \ingroup allocator Allocation and memory placement
+/// @{
+
+class C2LinearAllocation;
+class C2GraphicAllocation;
+
+/**
+ *  Allocators are used by the framework to allocate memory (allocations) for buffers. They can
+ *  support either 1D or 2D allocations.
+ *
+ *  \note In theory they could support both, but in practice, we will use only one or the other.
+ *
+ *  Never constructed on stack.
+ *
+ *  Allocators are provided by vendors.
+ */
+class C2Allocator {
+public:
+    /**
+     * Allocator ID type.
+     */
+    typedef uint32_t id_t;
+    enum : id_t {
+        BAD_ID = 0xBADD, // invalid allocator ID
+    };
+
+    /**
+     * Allocation types. This is a bitmask and is used in C2Allocator::Info
+     * to list the supported allocation types of an allocator.
+     */
+    enum type_t : uint32_t {
+        LINEAR  = 1 << 0, //
+        GRAPHIC = 1 << 1,
+    };
+
+    /**
+     * Information about an allocator.
+     *
+     * Allocators don't have a query API so all queriable information is stored here.
+     */
+    struct Traits {
+        C2String name;              ///< allocator name
+        id_t id;                    ///< allocator ID
+        type_t supportedTypes;      ///< supported allocation types
+        C2MemoryUsage minimumUsage; ///< usage that is minimally required for allocations
+        C2MemoryUsage maximumUsage; ///< usage that is maximally allowed for allocations
+    };
+
+    /**
+     * Returns the unique name of this allocator.
+     *
+     * This method MUST be "non-blocking" and return within 1ms.
+     *
+     * \return the name of this allocator.
+     * \retval an empty string if there was not enough memory to allocate the actual name.
+     */
+    virtual C2String getName() const = 0;
+
+    /**
+     * Returns a unique ID for this allocator. This ID is used to get this allocator from the
+     * allocator store, and to identify this allocator across all processes.
+     *
+     * This method MUST be "non-blocking" and return within 1ms.
+     *
+     * \return a unique ID for this allocator.
+     */
+    virtual id_t getId() const = 0;
+
+    /**
+     * Returns the allocator traits.
+     *
+     * This method MUST be "non-blocking" and return within 1ms.
+     *
+     * Allocators don't have a full-fledged query API, only this method.
+     *
+     * \return allocator information
+     */
+    virtual std::shared_ptr<const Traits> getTraits() const = 0;
+
+    /**
+     * Allocates a 1D allocation of given |capacity| and |usage|. If successful, the allocation is
+     * stored in |allocation|. Otherwise, |allocation| is set to 'nullptr'.
+     *
+     * \param capacity      the size of requested allocation (the allocation could be slightly
+     *                      larger, e.g. to account for any system-required alignment)
+     * \param usage         the memory usage info for the requested allocation. \note that the
+     *                      returned allocation may be later used/mapped with different usage.
+     *                      The allocator should layout the buffer to be optimized for this usage,
+     *                      but must support any usage. One exception: protected buffers can
+     *                      only be used in a protected scenario.
+     * \param allocation    pointer to where the allocation shall be stored on success. nullptr
+     *                      will be stored here on failure
+     *
+     * \retval C2_OK        the allocation was successful
+     * \retval C2_NO_MEMORY not enough memory to complete the allocation
+     * \retval C2_TIMED_OUT the allocation timed out
+     * \retval C2_REFUSED   no permission to complete the allocation
+     * \retval C2_BAD_VALUE capacity or usage are not supported (invalid) (caller error)
+     * \retval C2_OMITTED   this allocator does not support 1D allocations
+     * \retval C2_CORRUPTED some unknown, unrecoverable error occured during allocation (unexpected)
+     */
+    virtual c2_status_t newLinearAllocation(
+            uint32_t capacity __unused, C2MemoryUsage usage __unused,
+            std::shared_ptr<C2LinearAllocation> *allocation /* nonnull */) {
+        *allocation = nullptr;
+        return C2_OMITTED;
+    }
+
+    /**
+     * (Re)creates a 1D allocation from a native |handle|. If successful, the allocation is stored
+     * in |allocation|. Otherwise, |allocation| is set to 'nullptr'.
+     *
+     * \param handle      the handle for the existing allocation. On success, the allocation will
+     *                    take ownership of |handle|.
+     * \param allocation  pointer to where the allocation shall be stored on success. nullptr
+     *                    will be stored here on failure
+     *
+     * \retval C2_OK        the allocation was recreated successfully
+     * \retval C2_NO_MEMORY not enough memory to recreate the allocation
+     * \retval C2_TIMED_OUT the recreation timed out (unexpected)
+     * \retval C2_REFUSED   no permission to recreate the allocation
+     * \retval C2_BAD_VALUE invalid handle (caller error)
+     * \retval C2_OMITTED   this allocator does not support 1D allocations
+     * \retval C2_CORRUPTED some unknown, unrecoverable error occured during allocation (unexpected)
+     */
+    virtual c2_status_t priorLinearAllocation(
+            const C2Handle *handle __unused,
+            std::shared_ptr<C2LinearAllocation> *allocation /* nonnull */) {
+        *allocation = nullptr;
+        return C2_OMITTED;
+    }
+
+    /**
+     * Allocates a 2D allocation of given |width|, |height|, |format| and |usage|. If successful,
+     * the allocation is stored in |allocation|. Otherwise, |allocation| is set to 'nullptr'.
+     *
+     * \param width         the width of requested allocation (the allocation could be slightly
+     *                      larger, e.g. to account for any system-required alignment)
+     * \param height        the height of requested allocation (the allocation could be slightly
+     *                      larger, e.g. to account for any system-required alignment)
+     * \param format        the pixel format of requested allocation. This could be a vendor
+     *                      specific format.
+     * \param usage         the memory usage info for the requested allocation. \note that the
+     *                      returned allocation may be later used/mapped with different usage.
+     *                      The allocator should layout the buffer to be optimized for this usage,
+     *                      but must support any usage. One exception: protected buffers can
+     *                      only be used in a protected scenario.
+     * \param allocation    pointer to where the allocation shall be stored on success. nullptr
+     *                      will be stored here on failure
+     *
+     * \retval C2_OK        the allocation was successful
+     * \retval C2_NO_MEMORY not enough memory to complete the allocation
+     * \retval C2_TIMED_OUT the allocation timed out
+     * \retval C2_REFUSED   no permission to complete the allocation
+     * \retval C2_BAD_VALUE width, height, format or usage are not supported (invalid) (caller error)
+     * \retval C2_OMITTED   this allocator does not support 2D allocations
+     * \retval C2_CORRUPTED some unknown, unrecoverable error occured during allocation (unexpected)
+     */
+    virtual c2_status_t newGraphicAllocation(
+            uint32_t width __unused, uint32_t height __unused, uint32_t format __unused,
+            C2MemoryUsage usage __unused,
+            std::shared_ptr<C2GraphicAllocation> *allocation /* nonnull */) {
+        *allocation = nullptr;
+        return C2_OMITTED;
+    }
+
+    /**
+     * (Re)creates a 2D allocation from a native handle.  If successful, the allocation is stored
+     * in |allocation|. Otherwise, |allocation| is set to 'nullptr'.
+     *
+     * \param handle      the handle for the existing allocation. On success, the allocation will
+     *                    take ownership of |handle|.
+     * \param allocation  pointer to where the allocation shall be stored on success. nullptr
+     *                    will be stored here on failure
+     *
+     * \retval C2_OK        the allocation was recreated successfully
+     * \retval C2_NO_MEMORY not enough memory to recreate the allocation
+     * \retval C2_TIMED_OUT the recreation timed out (unexpected)
+     * \retval C2_REFUSED   no permission to recreate the allocation
+     * \retval C2_BAD_VALUE invalid handle (caller error)
+     * \retval C2_OMITTED   this allocator does not support 2D allocations
+     * \retval C2_CORRUPTED some unknown, unrecoverable error occured during recreation (unexpected)
+     */
+    virtual c2_status_t priorGraphicAllocation(
+            const C2Handle *handle __unused,
+            std::shared_ptr<C2GraphicAllocation> *allocation /* nonnull */) {
+        *allocation = nullptr;
+        return C2_OMITTED;
+    }
+
+    virtual ~C2Allocator() = default;
+protected:
+    C2Allocator() = default;
+};
+
+/**
+ * \ingroup linear allocator
+ * 1D allocation interface.
+ */
+class C2LinearAllocation : public _C2LinearCapacityAspect {
+public:
+    /**
+     * Maps a portion of an allocation starting from |offset| with |size| into local process memory.
+     * Stores the starting address into |addr|, or NULL if the operation was unsuccessful.
+     * |fence| will contain an acquire sync fence object. If it is already
+     * safe to access the buffer contents, then it will contain an empty (already fired) fence.
+     *
+     * \param offset        starting position of the portion to be mapped (this does not have to
+     *                      be page aligned)
+     * \param size          size of the portion to be mapped (this does not have to be page
+     *                      aligned)
+     * \param usage         the desired usage. \todo this must be kSoftwareRead and/or
+     *                      kSoftwareWrite.
+     * \param fence         a pointer to a fence object if an async mapping is requested. If
+     *                      not-null, and acquire fence will be stored here on success, or empty
+     *                      fence on failure. If null, the mapping will be synchronous.
+     * \param addr          a pointer to where the starting address of the mapped portion will be
+     *                      stored. On failure, nullptr will be stored here.
+     *
+     * \todo Only one portion can be mapped at the same time - this is true for gralloc, but there
+     *       is no need for this for 1D buffers.
+     * \todo Do we need to support sync operation as we could just wait for the fence?
+     *
+     * \retval C2_OK        the operation was successful
+     * \retval C2_REFUSED   no permission to map the portion
+     * \retval C2_TIMED_OUT the operation timed out
+     * \retval C2_DUPLICATE if the allocation is already mapped.
+     * \retval C2_NO_MEMORY not enough memory to complete the operation
+     * \retval C2_BAD_VALUE the parameters (offset/size) are invalid or outside the allocation, or
+     *                      the usage flags are invalid (caller error)
+     * \retval C2_CORRUPTED some unknown error prevented the operation from completing (unexpected)
+     */
+    virtual c2_status_t map(
+            size_t offset, size_t size, C2MemoryUsage usage, C2Fence *fence /* nullable */,
+            void **addr /* nonnull */) = 0;
+
+    /**
+     * Unmaps a portion of an allocation at |addr| with |size|. These must be parameters previously
+     * passed to and returned by |map|; otherwise, this operation is a no-op.
+     *
+     * \param addr          starting address of the mapped region
+     * \param size          size of the mapped region
+     * \param fence         a pointer to a fence object if an async unmapping is requested. If
+     *                      not-null, a release fence will be stored here on success, or empty fence
+     *                      on failure. This fence signals when the original allocation contains
+     *                      all changes that happened to the mapped region. If null, the unmapping
+     *                      will be synchronous.
+     *
+     * \retval C2_OK        the operation was successful
+     * \retval C2_TIMED_OUT the operation timed out
+     * \retval C2_NOT_FOUND if the allocation was not mapped previously.
+     * \retval C2_BAD_VALUE the parameters (addr/size) do not correspond to previously mapped
+     *                      regions (caller error)
+     * \retval C2_CORRUPTED some unknown error prevented the operation from completing (unexpected)
+     * \retval C2_REFUSED   no permission to unmap the portion (unexpected - system)
+     */
+    virtual c2_status_t unmap(void *addr, size_t size, C2Fence *fence /* nullable */) = 0;
+
+    /**
+     * Returns the allocator ID for this allocation. This is useful to put the handle into context.
+     */
+    virtual C2Allocator::id_t getAllocatorId() const = 0;
+
+    /**
+     * Returns a pointer to the allocation handle.
+     */
+    virtual const C2Handle *handle() const = 0;
+
+    /**
+     * Returns true if this is the same allocation as |other|.
+     */
+    virtual bool equals(const std::shared_ptr<C2LinearAllocation> &other) const = 0;
+
+protected:
+    // \todo should we limit allocation directly?
+    C2LinearAllocation(size_t capacity) : _C2LinearCapacityAspect(c2_min(capacity, UINT32_MAX)) {}
+    virtual ~C2LinearAllocation() = default;
+};
+
+class C2CircularBlock;
+class C2LinearBlock;
+class C2GraphicBlock;
+
+/**
+ *  Block pools are used by components to obtain output buffers in an efficient way. They can
+ *  support either linear (1D), circular (1D) or graphic (2D) blocks.
+ *
+ *  Block pools decouple the recycling of memory/allocations from the components. They are meant to
+ *  be an opaque service (there are no public APIs other than obtaining blocks) provided by the
+ *  platform. Block pools are also meant to decouple allocations from memory used by buffers. This
+ *  is accomplished by allowing pools to allot multiple memory 'blocks' on a single allocation. As
+ *  their name suggest, block pools maintain a pool of memory blocks. When a component asks for
+ *  a memory block, pools will try to return a free memory block already in the pool. If no such
+ *  block exists, they will allocate memory using the backing allocator and allot a block on that
+ *  allocation. When blocks are no longer used in the system, they are recycled back to the block
+ *  pool and are available as free blocks.
+ *
+ *  Never constructed on stack.
+ */
+class C2BlockPool {
+public:
+    /**
+     * Block pool ID type.
+     */
+    typedef uint64_t local_id_t;
+
+    enum : local_id_t {
+        BASIC_LINEAR = 0,  ///< ID of basic (unoptimized) block pool for fetching 1D blocks
+        BASIC_GRAPHIC = 1, ///< ID of basic (unoptimized) block pool for fetching 2D blocks
+        PLATFORM_START = 0x10,
+    };
+
+    /**
+     * Returns the ID for this block pool. This ID is used to get this block pool from the platform.
+     * It is only valid in the current process.
+     *
+     * This method MUST be "non-blocking" and return within 1ms.
+     *
+     * \return a local ID for this block pool.
+     */
+    virtual local_id_t getLocalId() const = 0;
+
+    /**
+     * Returns the ID of the backing allocator of this block pool.
+     *
+     * This method MUST be "non-blocking" and return within 1ms.
+     *
+     * \return the ID of the backing allocator of this block pool.
+     */
+    virtual C2Allocator::id_t getAllocatorId() const = 0;
+
+    /**
+     * Obtains a linear writeable block of given |capacity| and |usage|. If successful, the
+     * block is stored in |block|. Otherwise, |block| is set to 'nullptr'.
+     *
+     * \param capacity the size of requested block.
+     * \param usage    the memory usage info for the requested block. Returned blocks will be
+     *                 optimized for this usage, but may be used with any usage. One exception:
+     *                 protected blocks/buffers can only be used in a protected scenario.
+     * \param block    pointer to where the obtained block shall be stored on success. nullptr will
+     *                 be stored here on failure
+     *
+     * \retval C2_OK        the operation was successful
+     * \retval C2_NO_MEMORY not enough memory to complete any required allocation
+     * \retval C2_TIMED_OUT the operation timed out
+     * \retval C2_REFUSED   no permission to complete any required allocation
+     * \retval C2_BAD_VALUE capacity or usage are not supported (invalid) (caller error)
+     * \retval C2_OMITTED   this pool does not support linear blocks
+     * \retval C2_CORRUPTED some unknown, unrecoverable error occured during operation (unexpected)
+     */
+    virtual c2_status_t fetchLinearBlock(
+            uint32_t capacity __unused, C2MemoryUsage usage __unused,
+            std::shared_ptr<C2LinearBlock> *block /* nonnull */) {
+        *block = nullptr;
+        return C2_OMITTED;
+    }
+
+    /**
+     * Obtains a circular writeable block of given |capacity| and |usage|. If successful, the
+     * block is stored in |block|. Otherwise, |block| is set to 'nullptr'.
+     *
+     * \param capacity the size of requested circular block. (note: the size of the obtained
+     *                 block could be slightly larger, e.g. to accommodate any system-required
+     *                 alignment)
+     * \param usage    the memory usage info for the requested block. Returned blocks will be
+     *                 optimized for this usage, but may be used with any usage. One exception:
+     *                 protected blocks/buffers can only be used in a protected scenario.
+     * \param block    pointer to where the obtained block shall be stored on success. nullptr
+     *                 will be stored here on failure
+     *
+     * \retval C2_OK        the operation was successful
+     * \retval C2_NO_MEMORY not enough memory to complete any required allocation
+     * \retval C2_TIMED_OUT the operation timed out
+     * \retval C2_REFUSED   no permission to complete any required allocation
+     * \retval C2_BAD_VALUE capacity or usage are not supported (invalid) (caller error)
+     * \retval C2_OMITTED   this pool does not support circular blocks
+     * \retval C2_CORRUPTED some unknown, unrecoverable error occured during operation (unexpected)
+     */
+    virtual c2_status_t fetchCircularBlock(
+            uint32_t capacity __unused, C2MemoryUsage usage __unused,
+            std::shared_ptr<C2CircularBlock> *block /* nonnull */) {
+        *block = nullptr;
+        return C2_OMITTED;
+    }
+
+    /**
+     * Obtains a 2D graphic block of given |width|, |height|, |format| and |usage|. If successful,
+     * the block is stored in |block|. Otherwise, |block| is set to 'nullptr'.
+     *
+     * \param width  the width of requested block (the obtained block could be slightly larger, e.g.
+     *               to accommodate any system-required alignment)
+     * \param height the height of requested block (the obtained block could be slightly larger,
+     *               e.g. to accommodate any system-required alignment)
+     * \param format the pixel format of requested block. This could be a vendor specific format.
+     * \param usage  the memory usage info for the requested block. Returned blocks will be
+     *               optimized for this usage, but may be used with any usage. One exception:
+     *               protected blocks/buffers can only be used in a protected scenario.
+     * \param block  pointer to where the obtained block shall be stored on success. nullptr
+     *               will be stored here on failure
+     *
+     * \retval C2_OK        the operation was successful
+     * \retval C2_NO_MEMORY not enough memory to complete any required allocation
+     * \retval C2_TIMED_OUT the operation timed out
+     * \retval C2_REFUSED   no permission to complete any required allocation
+     * \retval C2_BAD_VALUE width, height, format or usage are not supported (invalid) (caller
+     *                      error)
+     * \retval C2_OMITTED   this pool does not support 2D blocks
+     * \retval C2_CORRUPTED some unknown, unrecoverable error occured during operation (unexpected)
+     */
+    virtual c2_status_t fetchGraphicBlock(
+            uint32_t width __unused, uint32_t height __unused, uint32_t format __unused,
+            C2MemoryUsage usage __unused,
+            std::shared_ptr<C2GraphicBlock> *block /* nonnull */) {
+        *block = nullptr;
+        return C2_OMITTED;
+    }
+
+    virtual ~C2BlockPool() = default;
+protected:
+    C2BlockPool() = default;
+};
+
+/// @}
+
+// ================================================================================================
+//  BLOCKS
+// ================================================================================================
+
+/**
+ * Blocks are sections of allocations. They can be either 1D or 2D.
+ */
+
+class C2LinearAllocation;
+
+/**
+ * A 1D block.
+ *
+ * \note capacity() is not meaningful for users of blocks; instead size() is the capacity of the
+ * usable portion. Use and offset() and size() if accessing the block directly through its handle
+ * to represent the allotted range of the underlying allocation to this block.
+ */
+class C2Block1D : public _C2LinearRangeAspect {
+public:
+    /**
+     * Returns the underlying handle for this allocation.
+     *
+     * \note that the block and its block pool has shared ownership of the handle
+     *       and if all references to the block are released, the underlying block
+     *       allocation may get reused even if a client keeps a clone of this handle.
+     */
+    const C2Handle *handle() const;
+
+    /**
+     * Returns the allocator's ID that created the underlying allocation for this block. This
+     * provides the context for understanding the handle.
+     */
+    C2Allocator::id_t getAllocatorId() const;
+
+protected:
+    class Impl;
+    /** construct a block. */
+    C2Block1D(std::shared_ptr<Impl> impl, const _C2LinearRangeAspect &range);
+
+    friend struct _C2BlockFactory;
+    std::shared_ptr<Impl> mImpl;
+};
+
+/**
+ * Read view provides read-only access for a linear memory segment.
+ *
+ * This class is copiable.
+ */
+class C2ReadView : public _C2LinearCapacityAspect {
+public:
+    /**
+     * \return pointer to the start of the block or nullptr on error.
+     *         This pointer is only valid during the lifetime of this view or until it is released.
+     */
+    const uint8_t *data() const;
+
+    /**
+     * Returns a portion of this view.
+     *
+     * \param offset  the start offset of the portion. \note This is clamped to the capacity of this
+     *              view.
+     * \param size    the size of the portion. \note This is clamped to the remaining data from offset.
+     *
+     * \return a read view containing a portion of this view
+     */
+    C2ReadView subView(size_t offset, size_t size) const;
+
+    /**
+     * \return error during the creation/mapping of this view.
+     */
+    c2_status_t error() const;
+
+    /**
+     * Releases this view. This sets error to C2_NO_INIT.
+     */
+    //void release();
+
+protected:
+    class Impl;
+    C2ReadView(std::shared_ptr<Impl> impl, uint32_t offset, uint32_t size);
+    explicit C2ReadView(c2_status_t error);
+
+private:
+    friend struct _C2BlockFactory;
+    std::shared_ptr<Impl> mImpl;
+    uint32_t mOffset; /**< offset into the linear block backing this read view */
+};
+
+/**
+ * Write view provides read/write access for a linear memory segment.
+ *
+ * This class is copiable. \todo movable only?
+ */
+class C2WriteView : public _C2EditableLinearRangeAspect {
+public:
+    /**
+     * Start of the block.
+     *
+     * \return pointer to the start of the block or nullptr on error.
+     *         This pointer is only valid during the lifetime of this view or until it is released.
+     */
+    uint8_t *base();
+
+    /**
+     * \return pointer to the block at the current offset or nullptr on error.
+     *         This pointer is only valid during the lifetime of this view or until it is released.
+     */
+    uint8_t *data();
+
+    /**
+     * \return error during the creation/mapping of this view.
+     */
+    c2_status_t error() const;
+
+    /**
+     * Releases this view. This sets error to C2_NO_INIT.
+     */
+    //void release();
+
+protected:
+    class Impl;
+    C2WriteView(std::shared_ptr<Impl> impl);
+    explicit C2WriteView(c2_status_t error);
+
+private:
+    friend struct _C2BlockFactory;
+    std::shared_ptr<Impl> mImpl;
+};
+
+/**
+ * A constant (read-only) linear block (portion of an allocation) with an acquire fence.
+ * Blocks are unmapped when created, and can be mapped into a read view on demand.
+ *
+ * This class is copiable and contains a reference to the allocation that it is based on.
+ */
+class C2ConstLinearBlock : public C2Block1D {
+public:
+    /**
+     * Maps this block into memory and returns a read view for it.
+     *
+     * \return a read view for this block.
+     */
+    C2Acquirable<C2ReadView> map() const;
+
+    /**
+     * Returns a portion of this block.
+     *
+     * \param offset  the start offset of the portion. \note This is clamped to the capacity of this
+     *              block.
+     * \param size    the size of the portion. \note This is clamped to the remaining data from offset.
+     *
+     * \return a constant linear block containing a portion of this block
+     */
+    C2ConstLinearBlock subBlock(size_t offset, size_t size) const;
+
+    /**
+     * Returns the acquire fence for this block.
+     *
+     * \return a fence that must be waited on before reading the block.
+     */
+    C2Fence fence() const { return mFence; }
+
+protected:
+    C2ConstLinearBlock(std::shared_ptr<Impl> impl, const _C2LinearRangeAspect &range, C2Fence mFence);
+
+private:
+    friend struct _C2BlockFactory;
+    C2Fence mFence;
+};
+
+/**
+ * Linear block is a writeable 1D block. Once written, it can be shared in whole or in parts with
+ * consumers/readers as read-only const linear block(s).
+ */
+class C2LinearBlock : public C2Block1D {
+public:
+    /**
+     * Maps this block into memory and returns a write view for it.
+     *
+     * \return a write view for this block.
+     */
+    C2Acquirable<C2WriteView> map();
+
+    /**
+     * Creates a read-only const linear block for a portion of this block; optionally protected
+     * by an acquire fence. There are two ways to use this:
+     *
+     * 1) share ready block after writing data into the block. In this case no fence shall be
+     *    supplied, and the block shall not be modified after calling this method.
+     * 2) share block metadata before actually (finishing) writing the data into the block. In
+     *    this case a fence must be supplied that will be triggered when the data is written.
+     *    The block shall be modified only until firing the event for the fence.
+     */
+    C2ConstLinearBlock share(size_t offset, size_t size, C2Fence fence);
+
+protected:
+    C2LinearBlock(std::shared_ptr<Impl> impl, const _C2LinearRangeAspect &range);
+
+    friend struct _C2BlockFactory;
+};
+
+/// @}
+
+/**************************************************************************************************
+  CIRCULAR BLOCKS AND VIEWS
+**************************************************************************************************/
+
+/// \defgroup circular Circular buffer support
+/// @{
+
+/**
+ * Circular blocks can be used to share data between a writer and a reader (and/or other consumers)-
+ * in a memory-efficient way by reusing a section of memory. Circular blocks are a bit more complex
+ * than single reader/single writer schemes to facilitate block-based consuming of data.
+ *
+ * They can operate in two modes:
+ *
+ * 1) one writer that creates blocks to be consumed (this model can be used by components)
+ *
+ * 2) one writer that writes continuously, and one reader that can creates blocks to be consumed
+ *    by further recipients (this model is used by the framework, and cannot be used by components.)
+ *
+ * Circular blocks have four segments with running pointers:
+ *  - reserved: data reserved and available for the writer
+ *  - committed: data committed by the writer and available to the reader (if present)
+ *  - used: data used by consumers (if present)
+ *  - available: unused data available to be reserved
+ */
+class C2CircularBlock : public C2Block1D {
+    // TODO: add methods
+
+private:
+    size_t mReserved __unused;   // end of reserved section
+    size_t mCommitted __unused;  // end of committed section
+    size_t mUsed __unused;       // end of used section
+    size_t mFree __unused;       // end of free section
+};
+
+class _C2CircularBlockSegment : public _C2LinearCapacityAspect {
+public:
+    /**
+     * Returns the available size for this segment.
+     *
+     * \return currently available size for this segment
+     */
+    size_t available() const;
+
+    /**
+     * Reserve some space for this segment from its current start.
+     *
+     * \param size    desired space in bytes
+     * \param fence   a pointer to an acquire fence. If non-null, the reservation is asynchronous and
+     *              a fence will be stored here that will be signaled when the reservation is
+     *              complete. If null, the reservation is synchronous.
+     *
+     * \retval C2_OK            the space was successfully reserved
+     * \retval C2_NO_MEMORY     the space requested cannot be reserved
+     * \retval C2_TIMED_OUT     the reservation timed out \todo when?
+     * \retval C2_CORRUPTED     some unknown error prevented reserving space. (unexpected)
+     */
+    c2_status_t reserve(size_t size, C2Fence *fence /* nullable */);
+
+    /**
+     * Abandons a portion of this segment. This will move to the beginning of this segment.
+     *
+     * \note This methods is only allowed if this segment is producing blocks.
+     *
+     * \param size    number of bytes to abandon
+     *
+     * \retval C2_OK            the data was successfully abandoned
+     * \retval C2_TIMED_OUT     the operation timed out (unexpected)
+     * \retval C2_CORRUPTED     some unknown error prevented abandoning the data (unexpected)
+     */
+    c2_status_t abandon(size_t size);
+
+    /**
+     * Share a portion as block(s) with consumers (these are moved to the used section).
+     *
+     * \note This methods is only allowed if this segment is producing blocks.
+     * \note Share does not move the beginning of the segment. (\todo add abandon/offset?)
+     *
+     * \param size    number of bytes to share
+     * \param fence   fence to be used for the section
+     * \param blocks  vector where the blocks of the section are appended to
+     *
+     * \retval C2_OK            the portion was successfully shared
+     * \retval C2_NO_MEMORY     not enough memory to share the portion
+     * \retval C2_TIMED_OUT     the operation timed out (unexpected)
+     * \retval C2_CORRUPTED     some unknown error prevented sharing the data (unexpected)
+     */
+    c2_status_t share(size_t size, C2Fence fence, std::vector<C2ConstLinearBlock> &blocks);
+
+    /**
+     * Returns the beginning offset of this segment from the start of this circular block.
+     *
+     * @return beginning offset
+     */
+    size_t begin();
+
+    /**
+     * Returns the end offset of this segment from the start of this circular block.
+     *
+     * @return end offset
+     */
+    size_t end();
+};
+
+/**
+ * A circular write-view is a dynamic mapped view for a segment of a circular block. Care must be
+ * taken when using this view so that only the section owned by the segment is modified.
+ */
+class C2CircularWriteView : public _C2LinearCapacityAspect {
+public:
+    /**
+     * Start of the circular block.
+     * \note the segment does not own this pointer.
+     *
+     * \return pointer to the start of the circular block or nullptr on error.
+     */
+    uint8_t *base();
+
+    /**
+     * \return error during the creation/mapping of this view.
+     */
+    c2_status_t error() const;
+};
+
+/**
+ * The writer of a circular buffer.
+ *
+ * Can commit data to a reader (not supported for components) OR share data blocks directly with a
+ * consumer.
+ *
+ * If a component supports outputting data into circular buffers, it must allocate a circular
+ * block and use a circular writer.
+ */
+class C2CircularWriter : public _C2CircularBlockSegment {
+public:
+    /**
+     * Commits a portion of this segment to the next segment. This moves the beginning of the
+     * segment.
+     *
+     * \param size    number of bytes to commit to the next segment
+     * \param fence   fence used for the commit (the fence must signal before the data is committed)
+     */
+    c2_status_t commit(size_t size, C2Fence fence);
+
+    /**
+     * Maps this block into memory and returns a write view for it.
+     *
+     * \return a write view for this block.
+     */
+    C2Acquirable<C2CircularWriteView> map();
+};
+
+/// @}
+
+/// \defgroup graphic Graphic Data Blocks
+/// @{
+
+/**
+ * C2Rect: rectangle type with non-negative coordinates.
+ *
+ * \note This struct has public fields without getters/setters. All methods are inline.
+ */
+struct C2Rect {
+// public:
+    uint32_t width;
+    uint32_t height;
+    uint32_t left;
+    uint32_t top;
+
+    constexpr inline C2Rect()
+        : C2Rect(0, 0, 0, 0) { }
+
+    constexpr inline C2Rect(uint32_t width_, uint32_t height_)
+        : C2Rect(width_, height_, 0, 0) { }
+
+    constexpr C2Rect inline at(uint32_t left_, uint32_t top_) const {
+        return C2Rect(width, height, left_, top_);
+    }
+
+    // utility methods
+
+    inline constexpr bool isEmpty() const {
+        return width == 0 || height == 0;
+    }
+
+    inline constexpr bool isValid() const {
+        return left <= ~width && top <= ~height;
+    }
+
+    inline constexpr operator bool() const {
+        return isValid() && !isEmpty();
+    }
+
+    inline constexpr bool operator!() const {
+        return !bool(*this);
+    }
+
+    C2_ALLOW_OVERFLOW
+    inline constexpr bool contains(const C2Rect &other) const {
+        if (!isValid() || !other.isValid()) {
+            return false;
+        } else {
+            return left <= other.left && top <= other.top
+                    && left + width >= other.left + other.width
+                    && top + height >= other.top + other.height;
+        }
+    }
+
+    inline constexpr bool operator==(const C2Rect &other) const {
+        if (!isValid()) {
+            return !other.isValid();
+        } else {
+            return left == other.left && top == other.top
+                    && width == other.width && height == other.height;
+        }
+    }
+
+    inline constexpr bool operator!=(const C2Rect &other) const {
+        return !operator==(other);
+    }
+
+    inline constexpr bool operator>=(const C2Rect &other) const {
+        return contains(other);
+    }
+
+    inline constexpr bool operator>(const C2Rect &other) const {
+        return contains(other) && !operator==(other);
+    }
+
+    inline constexpr bool operator<=(const C2Rect &other) const {
+        return other.contains(*this);
+    }
+
+    inline constexpr bool operator<(const C2Rect &other) const {
+        return other.contains(*this) && !operator==(other);
+    }
+
+    C2_ALLOW_OVERFLOW
+    inline constexpr uint32_t right() const {
+        return left + width;
+    }
+
+    C2_ALLOW_OVERFLOW
+    inline constexpr uint32_t bottom() const {
+        return top + height;
+    }
+
+    C2_ALLOW_OVERFLOW
+    inline constexpr C2Rect intersect(const C2Rect &other) const {
+        return C2Rect(c2_min(right(), other.right()) - c2_max(left, other.left),
+                      c2_min(bottom(), other.bottom()) - c2_max(top, other.top),
+                      c2_max(left, other.left),
+                      c2_max(top, other.top));
+    }
+
+    /** clamps right and bottom to top, left if they overflow */
+    inline constexpr C2Rect normalize() const {
+        return C2Rect(c2_max(left, right()) - left, c2_max(top, bottom()) - top, left, top);
+    }
+
+private:
+    /// note: potentially unusual argument order
+    constexpr inline C2Rect(uint32_t width_, uint32_t height_, uint32_t left_, uint32_t top_)
+        : width(width_),
+          height(height_),
+          left(left_),
+          top(top_) { }
+};
+
+/**
+ * Interface for objects that have a width and height (planar capacity).
+ */
+class _C2PlanarCapacityAspect {
+/// \name Planar capacity interface
+/// @{
+public:
+    inline constexpr uint32_t width() const { return _mWidth; }
+    inline constexpr uint32_t height() const { return _mHeight; }
+
+    inline constexpr operator C2Rect() const {
+        return C2Rect(_mWidth, _mHeight);
+    }
+
+protected:
+    inline constexpr _C2PlanarCapacityAspect(uint32_t width, uint32_t height)
+      : _mWidth(width), _mHeight(height) { }
+
+    inline explicit constexpr _C2PlanarCapacityAspect(const _C2PlanarCapacityAspect *parent)
+        : _mWidth(parent == nullptr ? 0 : parent->width()),
+          _mHeight(parent == nullptr ? 0 : parent->height()) { }
+
+private:
+    uint32_t _mWidth;
+    uint32_t _mHeight;
+/// @}
+};
+
+/**
+ * C2PlaneInfo: information on the layout of a singe flexible plane.
+ *
+ * Public fields without getters/setters.
+ */
+struct C2PlaneInfo {
+//public:
+    enum channel_t : uint32_t {
+        CHANNEL_Y,  ///< luma
+        CHANNEL_R,  ///< red
+        CHANNEL_G,  ///< green
+        CHANNEL_B,  ///< blue
+        CHANNEL_A,  ///< alpha
+        CHANNEL_CR, ///< Cr
+        CHANNEL_CB, ///< Cb
+    } channel;
+
+    int32_t colInc;       ///< column increment in bytes. may be negative
+    int32_t rowInc;       ///< row increment in bytes. may be negative
+
+    uint32_t colSampling; ///< subsampling compared to width (must be a power of 2)
+    uint32_t rowSampling; ///< subsampling compared to height (must be a power of 2)
+
+    uint32_t allocatedDepth; ///< size of each sample (must be a multiple of 8)
+    uint32_t bitDepth;       ///< significant bits per sample
+    /**
+     * the right shift of the significant bits in the sample. E.g. if a 10-bit significant
+     * value is laid out in a 16-bit allocation aligned to LSB (values 0-1023), rightShift
+     * would be 0 as the 16-bit value read from the sample does not need to be right shifted
+     * and can be used as is (after applying a 10-bit mask of 0x3FF).
+     *
+     * +--------+--------+
+     * |      VV|VVVVVVVV|
+     * +--------+--------+
+     *  15     8 7      0
+     *
+     * If the value is laid out aligned to MSB, rightShift would be 6, as the value read
+     * from the allocated sample must be right-shifted by 6 to get the actual sample value.
+     *
+     * +--------+--------+
+     * |VVVVVVVV|VV      |
+     * +--------+--------+
+     *  15     8 7      0
+     */
+    uint32_t rightShift;
+
+    enum endianness_t : uint32_t {
+        NATIVE,
+        LITTLE_END, // LITTLE_ENDIAN is reserved macro
+        BIG_END,    // BIG_ENDIAN is a reserved macro
+    } endianness; ///< endianness of the samples
+
+    /**
+     * The following two fields define the relation between multiple planes. If multiple planes are
+     * interleaved, they share a root plane (whichever plane's start address is the lowest), and
+     * |offset| is the offset of this plane inside the root plane (in bytes). |rootIx| is the index
+     * of the root plane. If a plane is independent, rootIx is its index and offset is 0.
+     */
+    uint32_t rootIx; ///< index of the root plane
+    uint32_t offset; ///< offset of this plane inside of the root plane
+
+    inline constexpr ssize_t minOffset(uint32_t width, uint32_t height) const {
+        ssize_t offs = 0;
+        if (width > 0 && colInc < 0) {
+            offs += colInc * (ssize_t)(width - 1);
+        }
+        if (height > 0 && rowInc < 0) {
+            offs += rowInc * (ssize_t)(height - 1);
+        }
+        return offs;
+    }
+
+    inline constexpr ssize_t maxOffset(uint32_t width, uint32_t height) const {
+        ssize_t offs = (allocatedDepth + 7) >> 3;
+        if (width > 0 && colInc > 0) {
+            offs += colInc * (ssize_t)(width - 1);
+        }
+        if (height > 0 && rowInc > 0) {
+            offs += rowInc * (ssize_t)(height - 1);
+        }
+        return offs;
+    }
+} C2_PACK;
+
+struct C2PlanarLayout {
+//public:
+    enum type_t : uint32_t {
+        TYPE_UNKNOWN = 0,
+        TYPE_YUV = 0x100,   ///< YUV image with 3 planes
+        TYPE_YUVA,          ///< YUVA image with 4 planes
+        TYPE_RGB,           ///< RGB image with 3 planes
+        TYPE_RGBA,          ///< RBGA image with 4 planes
+    };
+
+    type_t type;                    // image type
+    uint32_t numPlanes;             // number of component planes
+    uint32_t rootPlanes;            // number of layout planes (root planes)
+
+    enum plane_index_t : uint32_t {
+        PLANE_Y = 0,
+        PLANE_U = 1,
+        PLANE_V = 2,
+        PLANE_R = 0,
+        PLANE_G = 1,
+        PLANE_B = 2,
+        PLANE_A = 3,
+        MAX_NUM_PLANES = 4,
+    };
+
+    C2PlaneInfo planes[MAX_NUM_PLANES];
+};
+
+/**
+ * Aspect for objects that have a planar section (crop rectangle).
+ *
+ * This class is copiable.
+ */
+class _C2PlanarSectionAspect : public _C2PlanarCapacityAspect {
+/// \name Planar section interface
+/// @{
+private:
+    inline constexpr _C2PlanarSectionAspect(uint32_t width, uint32_t height, const C2Rect &crop)
+        : _C2PlanarCapacityAspect(width, height),
+          mCrop(C2Rect(std::min(width - std::min(crop.left, width), crop.width),
+                       std::min(height - std::min(crop.top, height), crop.height)).at(
+                               std::min(crop.left, width),
+                               std::min(crop.height, height))) {
+    }
+
+public:
+    // crop can be an empty rect, does not have to line up with subsampling
+    // NOTE: we do not support floating-point crop
+    inline constexpr C2Rect crop() const { return mCrop; }
+
+    /**
+     * Returns a child planar section for |crop|, where the capacity represents this section.
+     */
+    inline constexpr _C2PlanarSectionAspect childSection(const C2Rect &crop) const {
+        return _C2PlanarSectionAspect(
+                mCrop.width, mCrop.height,
+                // crop and translate |crop| rect
+                C2Rect(c2_min(mCrop.right() - c2_clamp(mCrop.left, crop.left, mCrop.right()),
+                              crop.width),
+                       c2_min(mCrop.bottom() - c2_clamp(mCrop.top, crop.top, mCrop.bottom()),
+                              crop.height))
+                .at(c2_clamp(mCrop.left, crop.left, mCrop.right()) - mCrop.left,
+                    c2_clamp(mCrop.top, crop.top, mCrop.bottom()) - mCrop.top));
+    }
+
+protected:
+    inline constexpr _C2PlanarSectionAspect(const _C2PlanarCapacityAspect *parent)
+        : _C2PlanarCapacityAspect(parent), mCrop(width(), height()) {}
+
+    inline constexpr _C2PlanarSectionAspect(const _C2PlanarCapacityAspect *parent, const C2Rect &crop)
+        : _C2PlanarCapacityAspect(parent),
+          mCrop(parent == nullptr ? C2Rect() : ((C2Rect)*parent).intersect(crop).normalize()) { }
+
+    inline constexpr _C2PlanarSectionAspect(const _C2PlanarSectionAspect *parent, const C2Rect &crop)
+        : _C2PlanarCapacityAspect(parent),
+          mCrop(parent == nullptr ? C2Rect() : parent->crop().intersect(crop).normalize()) { }
+
+private:
+    friend class _C2EditablePlanarSectionAspect;
+    C2Rect mCrop;
+/// @}
+};
+
+/**
+ * Aspect for objects that have an editable planar section (crop rectangle).
+ *
+ * This class is copiable.
+ */
+class _C2EditablePlanarSectionAspect : public _C2PlanarSectionAspect {
+/// \name Planar section interface
+/// @{
+    using _C2PlanarSectionAspect::_C2PlanarSectionAspect;
+
+public:
+    // crop can be an empty rect, does not have to line up with subsampling
+    // NOTE: we do not support floating-point crop
+    inline constexpr C2Rect crop() const { return mCrop; }
+
+    /**
+     *  Sets crop to crop intersected with [(0,0) .. (width, height)]
+     */
+    inline void setCrop_be(const C2Rect &crop) {
+        mCrop.left = std::min(width(), crop.left);
+        mCrop.top = std::min(height(), crop.top);
+        // It's guaranteed that mCrop.left <= width() && mCrop.top <= height()
+        mCrop.width = std::min(width() - mCrop.left, crop.width);
+        mCrop.height = std::min(height() - mCrop.top, crop.height);
+    }
+
+    /**
+     * If crop is within the dimensions of this object, it sets crop to it.
+     *
+     * \return true iff crop is within the dimensions of this object
+     */
+    inline bool setCrop(const C2Rect &crop) {
+        if (width() < crop.width || height() < crop.height
+                || width() - crop.width < crop.left || height() - crop.height < crop.top) {
+            return false;
+        }
+        mCrop = crop;
+        return true;
+    }
+/// @}
+};
+
+/**
+ * Utility class for safe range calculations using size_t-s.
+ */
+class C2PlanarSection : public _C2PlanarSectionAspect {
+public:
+    inline constexpr C2PlanarSection(const _C2PlanarCapacityAspect &parent, const C2Rect &crop)
+        : _C2PlanarSectionAspect(&parent, crop) { }
+
+    inline constexpr C2PlanarSection(const _C2PlanarSectionAspect &parent, const C2Rect &crop)
+        : _C2PlanarSectionAspect(&parent, crop) { }
+
+    inline constexpr C2PlanarSection intersect(const C2Rect &crop) const {
+        return C2PlanarSection(*this, crop);
+    }
+};
+
+/**
+ * Utility class for simple and safe planar capacity and section construction.
+ */
+class C2PlanarCapacity : public _C2PlanarCapacityAspect {
+public:
+    inline constexpr explicit C2PlanarCapacity(size_t width, size_t height)
+        : _C2PlanarCapacityAspect(c2_min(width, std::numeric_limits<uint32_t>::max()),
+                                  c2_min(height, std::numeric_limits<uint32_t>::max())) { }
+
+    inline constexpr C2PlanarSection section(const C2Rect &crop) const {
+        return C2PlanarSection(*this, crop);
+    }
+};
+
+
+/**
+ * \ingroup graphic allocator
+ * 2D allocation interface.
+ */
+class C2GraphicAllocation : public _C2PlanarCapacityAspect {
+public:
+    /**
+     * Maps a rectangular section (as defined by |rect|) of a 2D allocation into local process
+     * memory for flexible access. On success, it fills out |layout| with the plane specifications
+     * and fills the |addr| array with pointers to the first byte of the top-left pixel of each
+     * plane used. Otherwise, it leaves |layout| and |addr| untouched. |fence| will contain
+     * an acquire sync fence object. If it is already safe to access the
+     * buffer contents, then it will be an empty (already fired) fence.
+     *
+     * Safe regions for the pointer addresses returned can be gotten via C2LayoutInfo.minOffset()/
+     * maxOffset().
+     *
+     * \param rect          section to be mapped (this does not have to be aligned)
+     * \param usage         the desired usage. \todo this must be kSoftwareRead and/or
+     *                      kSoftwareWrite.
+     * \param fence         a pointer to a fence object if an async mapping is requested. If
+     *                      not-null, and acquire fence will be stored here on success, or empty
+     *                      fence on failure. If null, the mapping will be synchronous.
+     * \param layout        a pointer to where the mapped planes' descriptors will be
+     *                      stored. On failure, nullptr will be stored here.
+     * \param addr          pointer to an array with at least C2PlanarLayout::MAX_NUM_PLANES
+     *                      elements. Only layout.numPlanes elements will be modified on success.
+     *
+     * \retval C2_OK        the operation was successful
+     * \retval C2_REFUSED   no permission to map the section
+     * \retval C2_DUPLICATE there is already a mapped region and this allocation cannot support
+     *                      multi-mapping (caller error)
+     * \retval C2_TIMED_OUT the operation timed out
+     * \retval C2_NO_MEMORY not enough memory to complete the operation
+     * \retval C2_BAD_VALUE the parameters (rect) are invalid or outside the allocation, or the
+     *                      usage flags are invalid (caller error)
+     * \retval C2_CORRUPTED some unknown error prevented the operation from completing (unexpected)
+
+     */
+    virtual c2_status_t map(
+            C2Rect rect, C2MemoryUsage usage, C2Fence *fence,
+            C2PlanarLayout *layout /* nonnull */, uint8_t **addr /* nonnull */) = 0;
+
+    /**
+     * Unmaps a section of an allocation at |addr| with |rect|. These must be parameters previously
+     * passed to and returned by |map|; otherwise, this operation is a no-op.
+     *
+     * \param addr          pointer to an array with at least C2PlanarLayout::MAX_NUM_PLANES
+     *                      elements containing the starting addresses of the mapped layers
+     * \param rect          boundaries of the mapped section
+     * \param fence         a pointer to a fence object if an async unmapping is requested. If
+     *                      not-null, a release fence will be stored here on success, or empty fence
+     *                      on failure. This fence signals when the original allocation contains
+     *                      all changes that happened to the mapped section. If null, the unmapping
+     *                      will be synchronous.
+     *
+     * \retval C2_OK        the operation was successful
+     * \retval C2_TIMED_OUT the operation timed out
+     * \retval C2_NOT_FOUND there is no such mapped region (caller error)
+     * \retval C2_CORRUPTED some unknown error prevented the operation from completing (unexpected)
+     * \retval C2_REFUSED   no permission to unmap the section (unexpected - system)
+     */
+    virtual c2_status_t unmap(
+            uint8_t **addr /* nonnull */, C2Rect rect, C2Fence *fence /* nullable */) = 0;
+
+    /**
+     * Returns the allocator ID for this allocation. This is useful to put the handle into context.
+     */
+    virtual C2Allocator::id_t getAllocatorId() const = 0;
+
+    /**
+     * Returns a pointer to the allocation handle.
+     */
+    virtual const C2Handle *handle() const = 0;
+
+    /**
+     * Returns true if this is the same allocation as |other|.
+     */
+    virtual bool equals(const std::shared_ptr<const C2GraphicAllocation> &other) const = 0;
+
+protected:
+    using _C2PlanarCapacityAspect::_C2PlanarCapacityAspect;
+    virtual ~C2GraphicAllocation() = default;
+};
+
+class C2GraphicAllocation;
+
+/**
+ * A 2D block.
+ *
+ * \note width()/height() is not meaningful for users of blocks; instead, crop().width() and
+ * crop().height() is the capacity of the usable portion. Use and crop() if accessing the block
+ * directly through its handle to represent the allotted region of the underlying allocation to this
+ * block.
+ */
+class C2Block2D : public _C2PlanarSectionAspect {
+public:
+    /**
+     * Returns the underlying handle for this allocation.
+     *
+     * \note that the block and its block pool has shared ownership of the handle
+     *       and if all references to the block are released, the underlying block
+     *       allocation may get reused even if a client keeps a clone of this handle.
+     */
+    const C2Handle *handle() const;
+
+    /**
+     * Returns the allocator's ID that created the underlying allocation for this block. This
+     * provides the context for understanding the handle.
+     */
+    C2Allocator::id_t getAllocatorId() const;
+
+protected:
+    class Impl;
+    C2Block2D(std::shared_ptr<Impl> impl, const _C2PlanarSectionAspect &section);
+
+    friend struct _C2BlockFactory;
+    std::shared_ptr<Impl> mImpl;
+};
+
+/**
+ * Graphic view provides read or read-write access for a graphic block.
+ *
+ * This class is copiable.
+ *
+ * \note Due to the subsampling of graphic buffers, a read view must still contain a crop rectangle
+ * to ensure subsampling is followed. This results in nearly identical interface between read and
+ * write views, so C2GraphicView can encompass both of them.
+ */
+class C2GraphicView : public _C2EditablePlanarSectionAspect {
+public:
+    /**
+     * \return array of pointers (of layout().numPlanes elements) to the start of the planes or
+     * nullptr on error. Regardless of crop rect, they always point to the top-left corner of each
+     * plane. Access outside of the crop rect results in an undefined behavior.
+     */
+    const uint8_t *const *data() const;
+
+    /**
+     * \return array of pointers (of layout().numPlanes elements) to the start of the planes or
+     * nullptr on error. Regardless of crop rect, they always point to the top-left corner of each
+     * plane. Access outside of the crop rect results in an undefined behavior.
+     */
+    uint8_t *const *data();
+
+    /**
+     * \return layout of the graphic block to interpret the returned data.
+     */
+    const C2PlanarLayout layout() const;
+
+    /**
+     * Returns a section of this view.
+     *
+     * \param rect    the dimension of the section. \note This is clamped to the crop of this view.
+     *
+     * \return a read view containing the requested section of this view
+     */
+    const C2GraphicView subView(const C2Rect &rect) const;
+    C2GraphicView subView(const C2Rect &rect);
+
+    /**
+     * \return error during the creation/mapping of this view.
+     */
+    c2_status_t error() const;
+
+protected:
+    class Impl;
+    C2GraphicView(std::shared_ptr<Impl> impl, const _C2PlanarSectionAspect &section);
+    explicit C2GraphicView(c2_status_t error);
+
+private:
+    friend struct _C2BlockFactory;
+    std::shared_ptr<Impl> mImpl;
+};
+
+/**
+ * A constant (read-only) graphic block (portion of an allocation) with an acquire fence.
+ * Blocks are unmapped when created, and can be mapped into a read view on demand.
+ *
+ * This class is copiable and contains a reference to the allocation that it is based on.
+ */
+class C2ConstGraphicBlock : public C2Block2D {
+public:
+    /**
+     * Maps this block into memory and returns a read view for it.
+     *
+     * \return a read view for this block.
+     */
+    C2Acquirable<const C2GraphicView> map() const;
+
+    /**
+     * Returns a section of this block.
+     *
+     * \param rect    the coordinates of the section. \note This is clamped to the crop rectangle of
+     *              this block.
+     *
+     * \return a constant graphic block containing a portion of this block
+     */
+    C2ConstGraphicBlock subBlock(const C2Rect &rect) const;
+
+    /**
+     * Returns the acquire fence for this block.
+     *
+     * \return a fence that must be waited on before reading the block.
+     */
+    C2Fence fence() const { return mFence; }
+
+protected:
+    C2ConstGraphicBlock(
+            std::shared_ptr<Impl> impl, const _C2PlanarSectionAspect &section, C2Fence fence);
+
+private:
+    friend struct _C2BlockFactory;
+    C2Fence mFence;
+};
+
+/**
+ * Graphic block is a writeable 2D block. Once written, it can be shared in whole or in part with
+ * consumers/readers as read-only const graphic block.
+ */
+class C2GraphicBlock : public C2Block2D {
+public:
+    /**
+     * Maps this block into memory and returns a write view for it.
+     *
+     * \return a write view for this block.
+     */
+    C2Acquirable<C2GraphicView> map();
+
+    /**
+     * Creates a read-only const linear block for a portion of this block; optionally protected
+     * by an acquire fence. There are two ways to use this:
+     *
+     * 1) share ready block after writing data into the block. In this case no fence shall be
+     *    supplied, and the block shall not be modified after calling this method.
+     * 2) share block metadata before actually (finishing) writing the data into the block. In
+     *    this case a fence must be supplied that will be triggered when the data is written.
+     *    The block shall be modified only until firing the event for the fence.
+     */
+    C2ConstGraphicBlock share(const C2Rect &crop, C2Fence fence);
+
+protected:
+    C2GraphicBlock(std::shared_ptr<Impl> impl, const _C2PlanarSectionAspect &section);
+
+    friend struct _C2BlockFactory;
+};
+
+/// @}
+
+/// \defgroup buffer_onj Buffer objects
+/// @{
+
+// ================================================================================================
+//  BUFFERS
+// ================================================================================================
+
+/// \todo: Do we still need this?
+///
+// There are 2 kinds of buffers: linear or graphic. Linear buffers can contain a single block, or
+// a list of blocks (LINEAR_CHUNKS). Support for list of blocks is optional, and can allow consuming
+// data from circular buffers or scattered data sources without extra memcpy. Currently, list of
+// graphic blocks is not supported.
+
+class C2LinearBuffer;   // read-write buffer
+class C2GraphicBuffer;  // read-write buffer
+class C2LinearChunksBuffer;
+
+/**
+ * C2BufferData: the main, non-meta data of a buffer. A buffer can contain either linear blocks
+ * or graphic blocks, and can contain either a single block or multiple blocks. This is determined
+ * by its type.
+ */
+class C2BufferData {
+public:
+    /**
+     *  The type of buffer data.
+     */
+    enum type_t : uint32_t {
+        INVALID,            ///< invalid buffer type. Do not use.
+        LINEAR,             ///< the buffer contains a single linear block
+        LINEAR_CHUNKS,      ///< the buffer contains one or more linear blocks
+        GRAPHIC,            ///< the buffer contains a single graphic block
+        GRAPHIC_CHUNKS,     ///< the buffer contains one of more graphic blocks
+    };
+    typedef type_t Type; // deprecated
+
+    /**
+     * Gets the type of this buffer (data).
+     * \return the type of this buffer data.
+     */
+    type_t type() const;
+
+    /**
+     * Gets the linear blocks of this buffer.
+     * \return a constant list of const linear blocks of this buffer.
+     * \retval empty list if this buffer does not contain linear block(s).
+     */
+    const std::vector<C2ConstLinearBlock> linearBlocks() const;
+
+    /**
+     * Gets the graphic blocks of this buffer.
+     * \return a constant list of const graphic blocks of this buffer.
+     * \retval empty list if this buffer does not contain graphic block(s).
+     */
+    const std::vector<C2ConstGraphicBlock> graphicBlocks() const;
+
+private:
+    class Impl;
+    std::shared_ptr<Impl> mImpl;
+
+protected:
+    // no public constructor
+    explicit C2BufferData(const std::vector<C2ConstLinearBlock> &blocks);
+    explicit C2BufferData(const std::vector<C2ConstGraphicBlock> &blocks);
+};
+
+/**
+ * C2Buffer: buffer base class. These are always used as shared_ptrs. Though the underlying buffer
+ * objects (native buffers, ion buffers, or dmabufs) are reference-counted by the system,
+ * C2Buffers hold only a single reference.
+ *
+ * These objects cannot be used on the stack.
+ */
+class C2Buffer {
+public:
+    /**
+     * Gets the buffer's data.
+     *
+     * \return the buffer's data.
+     */
+    const C2BufferData data() const;
+
+    /**
+     * These will still work if used in onDeathNotify.
+     */
+#if 0
+    inline std::shared_ptr<C2LinearBuffer> asLinearBuffer() const {
+        return mType == LINEAR ? std::shared_ptr::reinterpret_cast<C2LinearBuffer>(this) : nullptr;
+    }
+
+    inline std::shared_ptr<C2GraphicBuffer> asGraphicBuffer() const {
+        return mType == GRAPHIC ? std::shared_ptr::reinterpret_cast<C2GraphicBuffer>(this) : nullptr;
+    }
+
+    inline std::shared_ptr<C2CircularBuffer> asCircularBuffer() const {
+        return mType == CIRCULAR ? std::shared_ptr::reinterpret_cast<C2CircularBuffer>(this) : nullptr;
+    }
+#endif
+
+    ///@name Pre-destroy notification handling
+    ///@{
+
+    /**
+     * Register for notification just prior to the destruction of this object.
+     */
+    typedef void (*OnDestroyNotify) (const C2Buffer *buf, void *arg);
+
+    /**
+     * Registers for a pre-destroy notification. This is called just prior to the destruction of
+     * this buffer (when this buffer is no longer valid.)
+     *
+     * \param onDestroyNotify   the notification callback
+     * \param arg               an arbitrary parameter passed to the callback
+     *
+     * \retval C2_OK        the registration was successful.
+     * \retval C2_DUPLICATE a notification was already registered for this callback and argument
+     * \retval C2_NO_MEMORY not enough memory to register for this callback
+     * \retval C2_CORRUPTED an unknown error prevented the registration (unexpected)
+     */
+    c2_status_t registerOnDestroyNotify(OnDestroyNotify onDestroyNotify, void *arg = nullptr);
+
+    /**
+     * Unregisters a previously registered pre-destroy notification.
+     *
+     * \param onDestroyNotify   the notification callback
+     * \param arg               an arbitrary parameter passed to the callback
+     *
+     * \retval C2_OK        the unregistration was successful.
+     * \retval C2_NOT_FOUND the notification was not found
+     * \retval C2_CORRUPTED an unknown error prevented the registration (unexpected)
+     */
+    c2_status_t unregisterOnDestroyNotify(OnDestroyNotify onDestroyNotify, void *arg = nullptr);
+
+    ///@}
+
+    virtual ~C2Buffer() = default;
+
+    ///@name Buffer-specific arbitrary metadata handling
+    ///@{
+
+    /**
+     * Gets the list of metadata associated with this buffer.
+     *
+     * \return a constant list of info objects associated with this buffer.
+     */
+    const std::vector<std::shared_ptr<const C2Info>> info() const;
+
+    /**
+     * Attaches (or updates) an (existing) metadata for this buffer.
+     * If the metadata is stream specific, the stream information will be reset.
+     *
+     * \param info Metadata to update
+     *
+     * \retval C2_OK        the metadata was successfully attached/updated.
+     * \retval C2_NO_MEMORY not enough memory to attach the metadata (this return value is not
+     *                      used if the same kind of metadata is already attached to the buffer).
+     */
+    c2_status_t setInfo(const std::shared_ptr<C2Info> &info);
+
+    /**
+     * Checks if there is a certain type of metadata attached to this buffer.
+     *
+     * \param index the parameter type of the metadata
+     *
+     * \return true iff there is a metadata with the parameter type attached to this buffer.
+     */
+    bool hasInfo(C2Param::Type index) const;
+
+    /**
+     * Checks if there is a certain type of metadata attached to this buffer, and returns a
+     * shared pointer to it if there is. Returns an empty shared pointer object (nullptr) if there
+     * is not.
+     *
+     * \param index the parameter type of the metadata
+     *
+     * \return shared pointer to the metadata.
+     */
+    std::shared_ptr<const C2Info> getInfo(C2Param::Type index) const;
+
+    /**
+     * Removes a metadata from the buffer.
+     */
+    std::shared_ptr<C2Info> removeInfo(C2Param::Type index);
+    ///@}
+
+    /**
+     * Creates a buffer containing a single linear block.
+     *
+     * \param block the content of the buffer.
+     *
+     * \return shared pointer to the created buffer.
+     */
+    static std::shared_ptr<C2Buffer> CreateLinearBuffer(const C2ConstLinearBlock &block);
+
+    /**
+     * Creates a buffer containing a single graphic block.
+     *
+     * \param block the content of the buffer.
+     *
+     * \return shared pointer to the created buffer.
+     */
+    static std::shared_ptr<C2Buffer> CreateGraphicBuffer(const C2ConstGraphicBlock &block);
+
+
+
+protected:
+    // no public constructor
+    explicit C2Buffer(const std::vector<C2ConstLinearBlock> &blocks);
+    explicit C2Buffer(const std::vector<C2ConstGraphicBlock> &blocks);
+
+private:
+    class Impl;
+    std::shared_ptr<Impl> mImpl;
+//    Type _mType;
+};
+
+/**
+ * An extension of C2Info objects that can contain arbitrary buffer data.
+ *
+ * \note This object is not describable and contains opaque data.
+ */
+class C2InfoBuffer {
+public:
+    /**
+     * Gets the index of this info object.
+     *
+     * \return the parameter index.
+     */
+    const C2Param::Index index() const;
+
+    /**
+     * Gets the buffer's data.
+     *
+     * \return the buffer's data.
+     */
+    const C2BufferData data() const;
+};
+
+/// @}
+
+/// \cond INTERNAL
+
+/// \todo These are no longer used
+
+/// \addtogroup linear
+/// @{
+
+/** \deprecated */
+class C2LinearBuffer
+    : public C2Buffer, public _C2LinearRangeAspect,
+      public std::enable_shared_from_this<C2LinearBuffer> {
+public:
+    /** \todo what is this? */
+    const C2Handle *handle() const;
+
+protected:
+    inline C2LinearBuffer(const C2ConstLinearBlock &block);
+
+private:
+    class Impl;
+    Impl *mImpl;
+};
+
+class C2ReadCursor;
+
+class C2WriteCursor {
+public:
+    uint32_t remaining() const; // remaining data to be read
+    void commit(); // commits the current position. discard data before current position
+    void reset() const;  // resets position to the last committed position
+    // slices off at most |size| bytes, and moves cursor ahead by the number of bytes
+    // sliced off.
+    C2ReadCursor slice(uint32_t size) const;
+    // slices off at most |size| bytes, and moves cursor ahead by the number of bytes
+    // sliced off.
+    C2WriteCursor reserve(uint32_t size);
+    // bool read(T&);
+    // bool write(T&);
+    C2Fence waitForSpace(uint32_t size);
+};
+
+/// @}
+
+/// \addtogroup graphic
+/// @{
+
+struct C2ColorSpace {
+//public:
+    enum Standard {
+        BT601,
+        BT709,
+        BT2020,
+        // TODO
+    };
+
+    enum Range {
+        LIMITED,
+        FULL,
+        // TODO
+    };
+
+    enum TransferFunction {
+        BT709Transfer,
+        BT2020Transfer,
+        HybridLogGamma2,
+        HybridLogGamma4,
+        // TODO
+    };
+};
+
+/** \deprecated */
+class C2GraphicBuffer : public C2Buffer {
+public:
+    // constant attributes
+    inline uint32_t width() const  { return mWidth; }
+    inline uint32_t height() const { return mHeight; }
+    inline uint32_t format() const { return mFormat; }
+    inline const C2MemoryUsage usage() const { return mUsage; }
+
+    // modifiable attributes
+
+
+    virtual const C2ColorSpace colorSpace() const = 0;
+    // best effort
+    virtual void setColorSpace_be(const C2ColorSpace &colorSpace) = 0;
+    virtual bool setColorSpace(const C2ColorSpace &colorSpace) = 0;
+
+    const C2Handle *handle() const;
+
+protected:
+    uint32_t mWidth;
+    uint32_t mHeight;
+    uint32_t mFormat;
+    C2MemoryUsage mUsage;
+
+    class Impl;
+    Impl *mImpl;
+};
+
+/// @}
+
+/// \endcond
+
+/// @}
+
+#endif  // C2BUFFER_H_