m_relation_history.h

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// Copyright 2021, Collabora, Ltd.
// SPDX-License-Identifier: BSL-1.0
/*!
 * @file
 * @brief Small utility for keeping track of the history of an xrt_space_relation, ie. for knowing where a HMD or
 * controller was in the past
 * @author Moshi Turner <moshiturner@protonmail.com>
 * @author Rylie Pavlik <rylie.pavlik@collabora.com>
 * @author Korcan Hussein <korcan.hussein@collabora.com>
 * @ingroup aux_util
 */
#pragma once
 
#include "xrt/xrt_defines.h"
 
#ifdef __cplusplus
extern "C" {
#endif
 
/**
 * @brief Opaque type for storing the history of a space relation in a ring buffer
 *
 * @note Unlike the bare C++ data structure @ref HistoryBuffer this wraps, **this is a thread safe interface**,
 * and is safe for concurrent access from multiple threads.
 * (It is using a simple mutex, not a reader/writer lock, but that is fine until proven to be a bottleneck.)
 *
 * @ingroup aux_util
 */
struct m_relation_history;
 
/**
 * @brief Describes how the resulting space relation for the desired time stamp was generated.
 *
 * @relates m_relation_history
 */
enum m_relation_history_result
{
        M_RELATION_HISTORY_RESULT_INVALID = 0,       //!< The supplied timestamp was invalid (0) or buffer was empty
        M_RELATION_HISTORY_RESULT_EXACT,             //!< The exact desired timestamp was found
        M_RELATION_HISTORY_RESULT_INTERPOLATED,      //!< The desired timestamp was between two entries
        M_RELATION_HISTORY_RESULT_PREDICTED,         //!< The desired timestamp was newer than the most recent entry
        M_RELATION_HISTORY_RESULT_REVERSE_PREDICTED, //!< The desired timestamp was older than the oldest entry
};
 
/*!
 * Creates an opaque relation_history object.
 *
 * @public @memberof m_relation_history
 */
void
m_relation_history_create(struct m_relation_history **rh);
 
/*!
 * Pushes a new pose to the history.
 *
 * If the history is full, it will also pop a pose out of the other side of the buffer.
 *
 * @return false if the timestamp is earlier than the most recent timestamp already recorded
 *
 * @public @memberof m_relation_history
 */
bool
m_relation_history_push(struct m_relation_history *rh, struct xrt_space_relation const *in_relation, int64_t timestamp);
 
/*!
 * Interpolates or extrapolates to the desired timestamp.
 *
 * Read-only operation - doesn't remove anything from the buffer or anything like that - you can call this as often as
 * you want.
 *
 * @public @memberof m_relation_history
 */
enum m_relation_history_result
m_relation_history_get(const struct m_relation_history *rh,
                       int64_t at_timestamp_ns,
                       struct xrt_space_relation *out_relation);
 
/*!
 * Estimates the movement (velocity and angular velocity) of a new relation based on
 * the latest relation found in the buffer (as returned by m_relation_history_get_latest).
 *
 * Read-only on m_relation_history and in_relation.
 * Copies in_relation->pose to out_relation->pose, and writes new flags and linear/angular velocities to
 * out_relation->pose. OK to alias in_relation and out_relation.
 *
 * @public @memberof m_relation_history
 */
bool
m_relation_history_estimate_motion(struct m_relation_history *rh,
                                   const struct xrt_space_relation *in_relation,
                                   int64_t timestamp,
                                   struct xrt_space_relation *out_relation);
 
/*!
 * Get the latest report in the buffer, if any.
 *
 * @param rh self
 * @param[out] out_time_ns Populated with the latest report time, if any
 * @param[out] out_relation Populated with the latest relation, if any
 *
 * @return false if the history is empty.
 *
 * @public @memberof m_relation_history
 */
bool
m_relation_history_get_latest(const struct m_relation_history *rh,
                              int64_t *out_time_ns,
                              struct xrt_space_relation *out_relation);
 
/*!
 * Returns the number of items in the history.
 *
 * @public @memberof m_relation_history
 */
uint32_t
m_relation_history_get_size(const struct m_relation_history *rh);
 
/*!
 * Clears the history from all of the items.
 *
 * @public @memberof m_relation_history
 */
void
m_relation_history_clear(struct m_relation_history *rh);
 
/*!
 * Destroys an opaque relation_history object.
 *
 * @public @memberof m_relation_history
 */
void
m_relation_history_destroy(struct m_relation_history **rh);
 
#ifdef __cplusplus
}
#endif
 
 
#ifdef __cplusplus
namespace xrt::auxiliary::math {
 
/*!
 * C++ interface for @ref m_relation_history, non-copyable/deletable.
 *
 * @ingroup aux_math
 */
class RelationHistory
{
public:
        /*!
         * @copydoc m_relation_history_result
         */
        typedef m_relation_history_result Result;
 
 
private:
        m_relation_history *mPtr{nullptr};
 
 
public:
        // clang-format off
        RelationHistory() noexcept { m_relation_history_create(&mPtr); }
        ~RelationHistory() { m_relation_history_destroy(&mPtr); }
        // clang-format on
 
        // Special non-copyable reference.
        RelationHistory(RelationHistory const &) = delete;
        RelationHistory(RelationHistory &&) = delete;
        RelationHistory &
        operator=(RelationHistory const &) = delete;
        RelationHistory &
        operator=(RelationHistory &&) = delete;
 
 
        /*!
         * @copydoc m_relation_history_push
         */
        bool
        push(xrt_space_relation const &relation, int64_t ts) noexcept
        {
                return m_relation_history_push(mPtr, &relation, ts);
        }
 
        /*!
         * @copydoc m_relation_history_get
         */
        Result
        get(int64_t at_time_ns, xrt_space_relation *out_relation) const noexcept
        {
                return m_relation_history_get(mPtr, at_time_ns, out_relation);
        }
 
        /*!
         * @copydoc m_relation_history_get_latest
         */
        bool
        get_latest(int64_t *out_time_ns, xrt_space_relation *out_relation) const noexcept
        {
                return m_relation_history_get_latest(mPtr, out_time_ns, out_relation);
        }
 
        /*!
         * @copydoc m_relation_history_get_size
         */
        size_t
        size() const noexcept
        {
                return m_relation_history_get_size(mPtr);
        }
 
        /*!
         * @copydoc m_relation_history_clear
         */
        void
        clear() noexcept
        {
                return m_relation_history_clear(mPtr);
        }
};
 
} // namespace xrt::auxiliary::math
#endif