tor-browser

pyramid.c (18549B)

---

/*
* 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.
*/

#include "aom_dsp/pyramid.h"
#include "aom_mem/aom_mem.h"
#include "aom_ports/bitops.h"
#include "aom_util/aom_pthread.h"

// TODO(rachelbarker): Move needed code from av1/ to aom_dsp/
#include "av1/common/resize.h"

#include <assert.h>
#include <string.h>

// Lifecycle:
// * Frame buffer alloc code calls aom_get_pyramid_alloc_size()
//   to work out how much space is needed for a given number of pyramid
//   levels. This is counted in the size checked against the max allocation
//   limit
// * Then calls aom_alloc_pyramid() to actually create the pyramid
// * Pyramid is initially marked as containing no valid data
// * Each pyramid layer is computed on-demand, the first time it is requested
// * Whenever frame buffer is reused, reset the counter of filled levels.
//   This invalidates all of the existing pyramid levels.
// * Whenever frame buffer is resized, reallocate pyramid

size_t aom_get_pyramid_alloc_size(int width, int height, bool image_is_16bit) {
 // Allocate the maximum possible number of layers for this width and height
 const int msb = get_msb(AOMMIN(width, height));
 const int n_levels = AOMMAX(msb - MIN_PYRAMID_SIZE_LOG2, 1);

 size_t alloc_size = 0;
 alloc_size += sizeof(ImagePyramid);
 alloc_size += n_levels * sizeof(PyramidLayer);

 // Calculate how much memory is needed for downscaled frame buffers
 size_t buffer_size = 0;

 // Work out if we need to allocate a few extra bytes for alignment.
 // aom_memalign() will ensure that the start of the allocation is aligned
 // to a multiple of PYRAMID_ALIGNMENT. But we want the first image pixel
 // to be aligned, not the first byte of the allocation.
 //
 // In the loop below, we ensure that the stride of every image is a multiple
 // of PYRAMID_ALIGNMENT. Thus the allocated size of each pyramid level will
 // also be a multiple of PYRAMID_ALIGNMENT. Thus, as long as we can get the
 // first pixel in the first pyramid layer aligned properly, that will
 // automatically mean that the first pixel of every row of every layer is
 // properly aligned too.
 //
 // Thus all we need to consider is the first pixel in the first layer.
 // This is located at offset
 //   extra_bytes + level_stride * PYRAMID_PADDING + PYRAMID_PADDING
 // bytes into the buffer. Since level_stride is a multiple of
 // PYRAMID_ALIGNMENT, we can ignore that. So we need
 //   extra_bytes + PYRAMID_PADDING = multiple of PYRAMID_ALIGNMENT
 //
 // To solve this, we can round PYRAMID_PADDING up to the next multiple
 // of PYRAMID_ALIGNMENT, then subtract the orginal value to calculate
 // how many extra bytes are needed.
 size_t first_px_offset =
     (PYRAMID_PADDING + PYRAMID_ALIGNMENT - 1) & ~(PYRAMID_ALIGNMENT - 1);
 size_t extra_bytes = first_px_offset - PYRAMID_PADDING;
 buffer_size += extra_bytes;

 // If the original image is stored in an 8-bit buffer, then we can point the
 // lowest pyramid level at that buffer rather than allocating a new one.
 int first_allocated_level = image_is_16bit ? 0 : 1;

 for (int level = first_allocated_level; level < n_levels; level++) {
   int level_width = width >> level;
   int level_height = height >> level;

   // Allocate padding for each layer
   int padded_width = level_width + 2 * PYRAMID_PADDING;
   int padded_height = level_height + 2 * PYRAMID_PADDING;

   // Align the layer stride to be a multiple of PYRAMID_ALIGNMENT
   // This ensures that, as long as the top-left pixel in this pyramid level is
   // properly aligned, then so will the leftmost pixel in every row of the
   // pyramid level.
   int level_stride =
       (padded_width + PYRAMID_ALIGNMENT - 1) & ~(PYRAMID_ALIGNMENT - 1);

   buffer_size += level_stride * padded_height;
 }

 alloc_size += buffer_size;

 return alloc_size;
}

ImagePyramid *aom_alloc_pyramid(int width, int height, bool image_is_16bit) {
 // Allocate the maximum possible number of layers for this width and height
 const int msb = get_msb(AOMMIN(width, height));
 const int n_levels = AOMMAX(msb - MIN_PYRAMID_SIZE_LOG2, 1);

 ImagePyramid *pyr = aom_calloc(1, sizeof(*pyr));
 if (!pyr) {
   return NULL;
 }

 pyr->layers = aom_calloc(n_levels, sizeof(*pyr->layers));
 if (!pyr->layers) {
   aom_free(pyr);
   return NULL;
 }

 pyr->max_levels = n_levels;
 pyr->filled_levels = 0;

 // Compute sizes and offsets for each pyramid level
 // These are gathered up first, so that we can allocate all pyramid levels
 // in a single buffer
 size_t buffer_size = 0;
 size_t *layer_offsets = aom_calloc(n_levels, sizeof(*layer_offsets));
 if (!layer_offsets) {
   aom_free(pyr->layers);
   aom_free(pyr);
   return NULL;
 }

 // Work out if we need to allocate a few extra bytes for alignment.
 // aom_memalign() will ensure that the start of the allocation is aligned
 // to a multiple of PYRAMID_ALIGNMENT. But we want the first image pixel
 // to be aligned, not the first byte of the allocation.
 //
 // In the loop below, we ensure that the stride of every image is a multiple
 // of PYRAMID_ALIGNMENT. Thus the allocated size of each pyramid level will
 // also be a multiple of PYRAMID_ALIGNMENT. Thus, as long as we can get the
 // first pixel in the first pyramid layer aligned properly, that will
 // automatically mean that the first pixel of every row of every layer is
 // properly aligned too.
 //
 // Thus all we need to consider is the first pixel in the first layer.
 // This is located at offset
 //   extra_bytes + level_stride * PYRAMID_PADDING + PYRAMID_PADDING
 // bytes into the buffer. Since level_stride is a multiple of
 // PYRAMID_ALIGNMENT, we can ignore that. So we need
 //   extra_bytes + PYRAMID_PADDING = multiple of PYRAMID_ALIGNMENT
 //
 // To solve this, we can round PYRAMID_PADDING up to the next multiple
 // of PYRAMID_ALIGNMENT, then subtract the orginal value to calculate
 // how many extra bytes are needed.
 size_t first_px_offset =
     (PYRAMID_PADDING + PYRAMID_ALIGNMENT - 1) & ~(PYRAMID_ALIGNMENT - 1);
 size_t extra_bytes = first_px_offset - PYRAMID_PADDING;
 buffer_size += extra_bytes;

 // If the original image is stored in an 8-bit buffer, then we can point the
 // lowest pyramid level at that buffer rather than allocating a new one.
 int first_allocated_level = image_is_16bit ? 0 : 1;

 for (int level = first_allocated_level; level < n_levels; level++) {
   PyramidLayer *layer = &pyr->layers[level];

   int level_width = width >> level;
   int level_height = height >> level;

   // Allocate padding for each layer
   int padded_width = level_width + 2 * PYRAMID_PADDING;
   int padded_height = level_height + 2 * PYRAMID_PADDING;

   // Align the layer stride to be a multiple of PYRAMID_ALIGNMENT
   // This ensures that, as long as the top-left pixel in this pyramid level is
   // properly aligned, then so will the leftmost pixel in every row of the
   // pyramid level.
   int level_stride =
       (padded_width + PYRAMID_ALIGNMENT - 1) & ~(PYRAMID_ALIGNMENT - 1);

   size_t level_alloc_start = buffer_size;
   size_t level_start =
       level_alloc_start + PYRAMID_PADDING * level_stride + PYRAMID_PADDING;

   buffer_size += level_stride * padded_height;

   layer_offsets[level] = level_start;
   layer->width = level_width;
   layer->height = level_height;
   layer->stride = level_stride;
 }

 pyr->buffer_alloc =
     aom_memalign(PYRAMID_ALIGNMENT, buffer_size * sizeof(*pyr->buffer_alloc));
 if (!pyr->buffer_alloc) {
   aom_free(pyr->layers);
   aom_free(pyr);
   aom_free(layer_offsets);
   return NULL;
 }

 // Fill in pointers for each level
 // If image is 8-bit, then the lowest level is left unconfigured for now,
 // and will be set up properly when the pyramid is filled in
 for (int level = first_allocated_level; level < n_levels; level++) {
   PyramidLayer *layer = &pyr->layers[level];
   layer->buffer = pyr->buffer_alloc + layer_offsets[level];
 }

#if CONFIG_MULTITHREAD
 pthread_mutex_init(&pyr->mutex, NULL);
#endif  // CONFIG_MULTITHREAD

 aom_free(layer_offsets);
 return pyr;
}

// Fill the border region of a pyramid frame.
// This must be called after the main image area is filled out.
// `img_buf` should point to the first pixel in the image area,
// ie. it should be pyr->level_buffer + pyr->level_loc[level].
static inline void fill_border(uint8_t *img_buf, const int width,
                              const int height, const int stride) {
 // Fill left and right areas
 for (int row = 0; row < height; row++) {
   uint8_t *row_start = &img_buf[row * stride];
   uint8_t left_pixel = row_start[0];
   memset(row_start - PYRAMID_PADDING, left_pixel, PYRAMID_PADDING);
   uint8_t right_pixel = row_start[width - 1];
   memset(row_start + width, right_pixel, PYRAMID_PADDING);
 }

 // Fill top area
 for (int row = -PYRAMID_PADDING; row < 0; row++) {
   uint8_t *row_start = &img_buf[row * stride];
   memcpy(row_start - PYRAMID_PADDING, img_buf - PYRAMID_PADDING,
          width + 2 * PYRAMID_PADDING);
 }

 // Fill bottom area
 uint8_t *last_row_start = &img_buf[(height - 1) * stride];
 for (int row = height; row < height + PYRAMID_PADDING; row++) {
   uint8_t *row_start = &img_buf[row * stride];
   memcpy(row_start - PYRAMID_PADDING, last_row_start - PYRAMID_PADDING,
          width + 2 * PYRAMID_PADDING);
 }
}

// Compute downsampling pyramid for a frame
//
// This function will ensure that the first `n_levels` levels of the pyramid
// are filled, unless the frame is too small to have this many levels.
// In that case, we will fill all available levels and then stop.
//
// Returns the actual number of levels filled, capped at n_levels,
// or -1 on error.
//
// This must only be called while holding frame_pyr->mutex
static inline int fill_pyramid(const YV12_BUFFER_CONFIG *frame, int bit_depth,
                              int n_levels, ImagePyramid *frame_pyr) {
 int already_filled_levels = frame_pyr->filled_levels;

 // This condition should already be enforced by aom_compute_pyramid
 assert(n_levels <= frame_pyr->max_levels);

 if (already_filled_levels >= n_levels) {
   return n_levels;
 }

 const int frame_width = frame->y_crop_width;
 const int frame_height = frame->y_crop_height;
 const int frame_stride = frame->y_stride;
 assert((frame_width >> n_levels) >= 0);
 assert((frame_height >> n_levels) >= 0);

 if (already_filled_levels == 0) {
   // Fill in largest level from the original image
   PyramidLayer *first_layer = &frame_pyr->layers[0];
   if (frame->flags & YV12_FLAG_HIGHBITDEPTH) {
     // For frames stored in a 16-bit buffer, we need to downconvert to 8 bits
     assert(first_layer->width == frame_width);
     assert(first_layer->height == frame_height);

     uint16_t *frame_buffer = CONVERT_TO_SHORTPTR(frame->y_buffer);
     uint8_t *pyr_buffer = first_layer->buffer;
     int pyr_stride = first_layer->stride;
     for (int y = 0; y < frame_height; y++) {
       uint16_t *frame_row = frame_buffer + y * frame_stride;
       uint8_t *pyr_row = pyr_buffer + y * pyr_stride;
       for (int x = 0; x < frame_width; x++) {
         pyr_row[x] = frame_row[x] >> (bit_depth - 8);
       }
     }

     fill_border(pyr_buffer, frame_width, frame_height, pyr_stride);
   } else {
     // For frames stored in an 8-bit buffer, we don't need to copy anything -
     // we can just reference the original image buffer
     first_layer->buffer = frame->y_buffer;
     first_layer->width = frame_width;
     first_layer->height = frame_height;
     first_layer->stride = frame_stride;
   }

   already_filled_levels = 1;
 }

 // Fill in the remaining levels through progressive downsampling
 for (int level = already_filled_levels; level < n_levels; ++level) {
   bool mem_status = false;
   PyramidLayer *prev_layer = &frame_pyr->layers[level - 1];
   uint8_t *prev_buffer = prev_layer->buffer;
   int prev_stride = prev_layer->stride;

   PyramidLayer *this_layer = &frame_pyr->layers[level];
   uint8_t *this_buffer = this_layer->buffer;
   int this_width = this_layer->width;
   int this_height = this_layer->height;
   int this_stride = this_layer->stride;

   // The width and height of the previous layer that needs to be considered to
   // derive the current layer frame.
   const int input_layer_width = this_width << 1;
   const int input_layer_height = this_height << 1;

   // Compute the this pyramid level by downsampling the current level.
   //
   // We downsample by a factor of exactly 2, clipping the rightmost and
   // bottommost pixel off of the current level if needed. We do this for
   // two main reasons:
   //
   // 1) In the disflow code, when stepping from a higher pyramid level to a
   //    lower pyramid level, we need to not just interpolate the flow field
   //    but also to scale each flow vector by the upsampling ratio.
   //    So it is much more convenient if this ratio is simply 2.
   //
   // 2) Up/downsampling by a factor of 2 can be implemented much more
   //    efficiently than up/downsampling by a generic ratio.
   //    TODO(rachelbarker): Use optimized downsample-by-2 function

   // SIMD support has been added specifically for cases where the downsample
   // factor is exactly 2. In such instances, horizontal and vertical resizing
   // is performed utilizing the down2_symeven() function, which considers the
   // even dimensions of the input layer.
   if (should_resize_by_half(input_layer_height, input_layer_width,
                             this_height, this_width)) {
     assert(input_layer_height % 2 == 0 && input_layer_width % 2 == 0 &&
            "Input width or height cannot be odd.");
     mem_status = av1_resize_plane_to_half(
         prev_buffer, input_layer_height, input_layer_width, prev_stride,
         this_buffer, this_height, this_width, this_stride);
   } else {
     mem_status = av1_resize_plane(prev_buffer, input_layer_height,
                                   input_layer_width, prev_stride, this_buffer,
                                   this_height, this_width, this_stride);
   }

   // Terminate early in cases of memory allocation failure.
   if (!mem_status) {
     frame_pyr->filled_levels = n_levels;
     return -1;
   }

   fill_border(this_buffer, this_width, this_height, this_stride);
 }

 frame_pyr->filled_levels = n_levels;
 return n_levels;
}

// 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.
//
// This function will ensure that the first `n_levels` levels of the pyramid
// are filled, unless the frame is too small to have this many levels.
// In that case, we will fill all available levels and then stop.
// No matter how small the frame is, at least one level is guaranteed
// to be filled.
//
// Returns the actual number of levels filled, capped at n_levels,
// or -1 on error.
int aom_compute_pyramid(const YV12_BUFFER_CONFIG *frame, int bit_depth,
                       int n_levels, ImagePyramid *pyr) {
 assert(pyr);

 // Per the comments in the ImagePyramid struct, we must take this mutex
 // before reading or writing the filled_levels field, and hold it while
 // computing any additional pyramid levels, to ensure proper behaviour
 // when multithreading is used
#if CONFIG_MULTITHREAD
 pthread_mutex_lock(&pyr->mutex);
#endif  // CONFIG_MULTITHREAD

 n_levels = AOMMIN(n_levels, pyr->max_levels);
 int result = n_levels;
 if (pyr->filled_levels < n_levels) {
   // Compute any missing levels that we need
   result = fill_pyramid(frame, bit_depth, n_levels, pyr);
 }

 // At this point, as long as result >= 0, the requested number of pyramid
 // levels are guaranteed to be valid, and can be safely read from without
 // holding the mutex any further
 assert(IMPLIES(result >= 0, pyr->filled_levels >= n_levels));
#if CONFIG_MULTITHREAD
 pthread_mutex_unlock(&pyr->mutex);
#endif  // CONFIG_MULTITHREAD
 return result;
}

#ifndef NDEBUG
// Check if a pyramid has already been computed to at least n levels
// This is mostly a debug helper - as it is necessary to hold pyr->mutex
// while reading the number of already-computed levels, we cannot just write:
//   assert(pyr->filled_levels >= n_levels);
// This function allows the check to be correctly written as:
//   assert(aom_is_pyramid_valid(pyr, n_levels));
//
// Note: This deliberately does not restrict n_levels based on the maximum
// number of permitted levels for the frame size. This allows the check to
// catch cases where the caller forgets to handle the case where
// max_levels is less than the requested number of levels
bool aom_is_pyramid_valid(ImagePyramid *pyr, int n_levels) {
 assert(pyr);

 // Per the comments in the ImagePyramid struct, we must take this mutex
 // before reading or writing the filled_levels field, to ensure proper
 // behaviour when multithreading is used
#if CONFIG_MULTITHREAD
 pthread_mutex_lock(&pyr->mutex);
#endif  // CONFIG_MULTITHREAD

 bool result = (pyr->filled_levels >= n_levels);

#if CONFIG_MULTITHREAD
 pthread_mutex_unlock(&pyr->mutex);
#endif  // CONFIG_MULTITHREAD

 return result;
}
#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) {
 if (pyr) {
#if CONFIG_MULTITHREAD
   pthread_mutex_lock(&pyr->mutex);
#endif  // CONFIG_MULTITHREAD
   pyr->filled_levels = 0;
#if CONFIG_MULTITHREAD
   pthread_mutex_unlock(&pyr->mutex);
#endif  // CONFIG_MULTITHREAD
 }
}

// Release the memory associated with a pyramid
void aom_free_pyramid(ImagePyramid *pyr) {
 if (pyr) {
#if CONFIG_MULTITHREAD
   pthread_mutex_destroy(&pyr->mutex);
#endif  // CONFIG_MULTITHREAD
   aom_free(pyr->buffer_alloc);
   aom_free(pyr->layers);
   aom_free(pyr);
 }
}