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+/*
+ * Copyright (c) 2022, 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_PYRAMID_H_
+#define AOM_AOM_DSP_PYRAMID_H_
+
+#include <stddef.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+#include "config/aom_config.h"
+
+#include "aom_scale/yv12config.h"
+#include "aom_util/aom_thread.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Minimum dimensions of a downsampled image
+#define MIN_PYRAMID_SIZE_LOG2 3
+#define MIN_PYRAMID_SIZE (1 << MIN_PYRAMID_SIZE_LOG2)
+
+// Size of border around each pyramid image, in pixels
+// Similarly to the border around regular image buffers, this border is filled
+// with copies of the outermost pixels of the frame, to allow for more efficient
+// convolution code
+// TODO(rachelbarker): How many pixels do we actually need here?
+// I think we only need 9 for disflow, but how many for corner matching?
+#define PYRAMID_PADDING 16
+
+// Byte alignment of each line within the image pyramids.
+// That is, the first pixel inside the image (ie, not in the border region),
+// on each row of each pyramid level, is aligned to this byte alignment.
+// This value must be a power of 2.
+#define PYRAMID_ALIGNMENT 32
+
+typedef struct {
+  uint8_t *buffer;
+  int width;
+  int height;
+  int stride;
+} PyramidLayer;
+
+// Struct for an image pyramid
+typedef struct image_pyramid {
+#if CONFIG_MULTITHREAD
+  // Mutex which is used to prevent the pyramid 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
+  // Flag indicating whether the pyramid contains valid data
+  bool valid;
+  // Number of allocated/filled levels in this pyramid
+  int n_levels;
+  // Pointer to allocated buffer
+  uint8_t *buffer_alloc;
+  // Data for each level
+  // The `buffer` pointers inside this array point into the region which
+  // is stored in the `buffer_alloc` field here
+  PyramidLayer *layers;
+} ImagePyramid;
+
+size_t aom_get_pyramid_alloc_size(int width, int height, int n_levels,
+                                  bool image_is_16bit);
+
+ImagePyramid *aom_alloc_pyramid(int width, int height, int n_levels,
+                                bool image_is_16bit);
+
+// Fill out a downsampling pyramid for a given frame.
+//
+// The top level (index 0) will always be an 8-bit copy of the input frame,
+// regardless of the input bit depth. Additional levels are then downscaled
+// by powers of 2.
+//
+// For small input frames, the number of levels actually constructed
+// will be limited so that the smallest image is at least MIN_PYRAMID_SIZE
+// pixels along each side.
+//
+// However, if the input frame has a side of length < MIN_PYRAMID_SIZE,
+// we will still construct the top level.
+bool aom_compute_pyramid(const YV12_BUFFER_CONFIG *frame, int bit_depth,
+                         ImagePyramid *pyr);
+
+#ifndef NDEBUG
+// Check if a pyramid has already been computed.
+// This is mostly a debug helper - as it is necessary to hold pyr->mutex
+// while reading the valid flag, we cannot just write:
+//   assert(pyr->valid);
+// This function allows the check to be correctly written as:
+//   assert(aom_is_pyramid_valid(pyr));
+bool aom_is_pyramid_valid(ImagePyramid *pyr);
+#endif
+
+// Mark a pyramid as no longer containing valid data.
+// This must be done whenever the corresponding frame buffer is reused
+void aom_invalidate_pyramid(ImagePyramid *pyr);
+
+// Release the memory associated with a pyramid
+void aom_free_pyramid(ImagePyramid *pyr);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif  // AOM_AOM_DSP_PYRAMID_H_