src/utils/rescaler_utils.c

// Copyright 2012 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
// Rescaling functions
//
// Author: Skal (pascal.massimino@gmail.com)

#include <assert.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include "src/dsp/dsp.h"
#include "src/utils/rescaler_utils.h"
#include "src/utils/utils.h"

//------------------------------------------------------------------------------

int WebPRescalerInit(WebPRescaler* const rescaler,
                     int src_width, int src_height,
                     uint8_t* const dst,
                     int dst_width, int dst_height, int dst_stride,
                     int num_channels, rescaler_t* const work) {
  const int x_add = src_width, x_sub = dst_width;
  const int y_add = src_height, y_sub = dst_height;
  const uint64_t total_size = 2ull * dst_width * num_channels * sizeof(*work);
  if (!CheckSizeOverflow(total_size)) return 0;

  rescaler->x_expand = (src_width < dst_width);
  rescaler->y_expand = (src_height < dst_height);
  rescaler->src_width = src_width;
  rescaler->src_height = src_height;
  rescaler->dst_width = dst_width;
  rescaler->dst_height = dst_height;
  rescaler->src_y = 0;
  rescaler->dst_y = 0;
  rescaler->dst = dst;
  rescaler->dst_stride = dst_stride;
  rescaler->num_channels = num_channels;

  // for 'x_expand', we use bilinear interpolation
  rescaler->x_add = rescaler->x_expand ? (x_sub - 1) : x_add;
  rescaler->x_sub = rescaler->x_expand ? (x_add - 1) : x_sub;
  if (!rescaler->x_expand) {  // fx_scale is not used otherwise
    rescaler->fx_scale = WEBP_RESCALER_FRAC(1, rescaler->x_sub);
  }
  // vertical scaling parameters
  rescaler->y_add = rescaler->y_expand ? y_add - 1 : y_add;
  rescaler->y_sub = rescaler->y_expand ? y_sub - 1 : y_sub;
  rescaler->y_accum = rescaler->y_expand ? rescaler->y_sub : rescaler->y_add;
  if (!rescaler->y_expand) {
    // This is WEBP_RESCALER_FRAC(dst_height, x_add * y_add) without the cast.
    // Its value is <= WEBP_RESCALER_ONE, because dst_height <= rescaler->y_add
    // and rescaler->x_add >= 1;
    const uint64_t num = (uint64_t)dst_height * WEBP_RESCALER_ONE;
    const uint64_t den = (uint64_t)rescaler->x_add * rescaler->y_add;
    const uint64_t ratio = num / den;
    if (ratio != (uint32_t)ratio) {
      // When ratio == WEBP_RESCALER_ONE, we can't represent the ratio with the
      // current fixed-point precision. This happens when src_height ==
      // rescaler->y_add (which == src_height), and rescaler->x_add == 1.
      // => We special-case fxy_scale = 0, in WebPRescalerExportRow().
      rescaler->fxy_scale = 0;
    } else {
      rescaler->fxy_scale = (uint32_t)ratio;
    }
    rescaler->fy_scale = WEBP_RESCALER_FRAC(1, rescaler->y_sub);
  } else {
    rescaler->fy_scale = WEBP_RESCALER_FRAC(1, rescaler->x_add);
    // rescaler->fxy_scale is unused here.
  }
  rescaler->irow = work;
  rescaler->frow = work + num_channels * dst_width;
  memset(work, 0, (size_t)total_size);

  WebPRescalerDspInit();
  return 1;
}

int WebPRescalerGetScaledDimensions(int src_width, int src_height,
                                    int* const scaled_width,
                                    int* const scaled_height) {
  assert(scaled_width != NULL);
  assert(scaled_height != NULL);
  {
    int width = *scaled_width;
    int height = *scaled_height;
    const int max_size = INT_MAX / 2;

    // if width is unspecified, scale original proportionally to height ratio.
    if (width == 0 && src_height > 0) {
      width =
          (int)(((uint64_t)src_width * height + src_height - 1) / src_height);
    }
    // if height is unspecified, scale original proportionally to width ratio.
    if (height == 0 && src_width > 0) {
      height =
          (int)(((uint64_t)src_height * width + src_width - 1) / src_width);
    }
    // Check if the overall dimensions still make sense.
    if (width <= 0 || height <= 0 || width > max_size || height > max_size) {
      return 0;
    }

    *scaled_width = width;
    *scaled_height = height;
    return 1;
  }
}

//------------------------------------------------------------------------------
// all-in-one calls

int WebPRescaleNeededLines(const WebPRescaler* const rescaler,
                           int max_num_lines) {
  const int num_lines =
      (rescaler->y_accum + rescaler->y_sub - 1) / rescaler->y_sub;
  return (num_lines > max_num_lines) ? max_num_lines : num_lines;
}

int WebPRescalerImport(WebPRescaler* const rescaler, int num_lines,
                       const uint8_t* src, int src_stride) {
  int total_imported = 0;
  while (total_imported < num_lines &&
         !WebPRescalerHasPendingOutput(rescaler)) {
    if (rescaler->y_expand) {
      rescaler_t* const tmp = rescaler->irow;
      rescaler->irow = rescaler->frow;
      rescaler->frow = tmp;
    }
    WebPRescalerImportRow(rescaler, src);
    if (!rescaler->y_expand) {    // Accumulate the contribution of the new row.
      int x;
      for (x = 0; x < rescaler->num_channels * rescaler->dst_width; ++x) {
        rescaler->irow[x] += rescaler->frow[x];
      }
    }
    ++rescaler->src_y;
    src += src_stride;
    ++total_imported;
    rescaler->y_accum -= rescaler->y_sub;
  }
  return total_imported;
}

int WebPRescalerExport(WebPRescaler* const rescaler) {
  int total_exported = 0;
  while (WebPRescalerHasPendingOutput(rescaler)) {
    WebPRescalerExportRow(rescaler);
    ++total_exported;
  }
  return total_exported;
}

//------------------------------------------------------------------------------