aom_dsp/flow_estimation/corner_detect.h

/*
 * Copyright (c) 2016, Alliance for Open Media. All rights reserved
 *
 * This source code is subject to the terms of the BSD 2 Clause License and
 * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
 * was not distributed with this source code in the LICENSE file, you can
 * obtain it at www.aomedia.org/license/software. If the Alliance for Open
 * Media Patent License 1.0 was not distributed with this source code in the
 * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
 */

#ifndef AOM_AOM_DSP_FLOW_ESTIMATION_CORNER_DETECT_H_
#define AOM_AOM_DSP_FLOW_ESTIMATION_CORNER_DETECT_H_

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <memory.h>

#include "aom_dsp/pyramid.h"
#include "aom_util/aom_thread.h"

#ifdef __cplusplus
extern "C" {
#endif

#define MAX_CORNERS 4096

typedef struct corner_list {
#if CONFIG_MULTITHREAD
  // Mutex which is used to prevent the corner list from being computed twice
  // at the same time
  //
  // Semantics:
  // * This mutex must be held whenever reading or writing the `valid` flag
  //
  // * This mutex must also be held while computing the image pyramid,
  //   to ensure that only one thread may do so at a time.
  //
  // * However, once you have read the valid flag and seen a true value,
  //   it is safe to drop the mutex and read from the remaining fields.
  //   This is because, once the image pyramid is computed, its contents
  //   will not be changed until the parent frame buffer is recycled,
  //   which will not happen until there are no more outstanding references
  //   to the frame buffer.
  pthread_mutex_t mutex;
#endif  // CONFIG_MULTITHREAD
  // Flag indicating whether the corner list contains valid data
  bool valid;
  // Number of corners found
  int num_corners;
  // (x, y) coordinates of each corner
  int corners[2 * MAX_CORNERS];
} CornerList;

size_t av1_get_corner_list_size(void);

CornerList *av1_alloc_corner_list(void);

bool av1_compute_corner_list(const ImagePyramid *pyr, CornerList *corners);

#ifndef NDEBUG
// Check if a corner list has already been computed.
// This is mostly a debug helper - as it is necessary to hold corners->mutex
// while reading the valid flag, we cannot just write:
//   assert(corners->valid);
// This function allows the check to be correctly written as:
//   assert(aom_is_corner_list_valid(corners));
bool aom_is_corner_list_valid(CornerList *corners);
#endif

void av1_invalidate_corner_list(CornerList *corners);

void av1_free_corner_list(CornerList *corners);

#ifdef __cplusplus
}
#endif

#endif  // AOM_AOM_DSP_FLOW_ESTIMATION_CORNER_DETECT_H_