Coverage Report

Created: 2024-07-27 06:27

/src/libwebp/src/enc/alpha_enc.c
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// Copyright 2011 Google Inc. All Rights Reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the COPYING file in the root of the source
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// tree. An additional intellectual property rights grant can be found
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// in the file PATENTS. All contributing project authors may
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// be found in the AUTHORS file in the root of the source tree.
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// -----------------------------------------------------------------------------
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//
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// Alpha-plane compression.
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//
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// Author: Skal (pascal.massimino@gmail.com)
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#include <assert.h>
15
#include <stdlib.h>
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#include <string.h>
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18
#include "src/enc/vp8i_enc.h"
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#include "src/dsp/dsp.h"
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#include "src/utils/filters_utils.h"
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#include "src/utils/quant_levels_utils.h"
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#include "src/utils/utils.h"
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#include "src/webp/encode.h"
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#include "src/webp/format_constants.h"
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// -----------------------------------------------------------------------------
27
// Encodes the given alpha data via specified compression method 'method'.
28
// The pre-processing (quantization) is performed if 'quality' is less than 100.
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// For such cases, the encoding is lossy. The valid range is [0, 100] for
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// 'quality' and [0, 1] for 'method':
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//   'method = 0' - No compression;
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//   'method = 1' - Use lossless coder on the alpha plane only
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// 'filter' values [0, 4] correspond to prediction modes none, horizontal,
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// vertical & gradient filters. The prediction mode 4 will try all the
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// prediction modes 0 to 3 and pick the best one.
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// 'effort_level': specifies how much effort must be spent to try and reduce
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//  the compressed output size. In range 0 (quick) to 6 (slow).
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//
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// 'output' corresponds to the buffer containing compressed alpha data.
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//          This buffer is allocated by this method and caller should call
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//          WebPSafeFree(*output) when done.
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// 'output_size' corresponds to size of this compressed alpha buffer.
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//
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// Returns 1 on successfully encoding the alpha and
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//         0 if either:
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//           invalid quality or method, or
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//           memory allocation for the compressed data fails.
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#include "src/enc/vp8li_enc.h"
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static int EncodeLossless(const uint8_t* const data, int width, int height,
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                          int effort_level,  // in [0..6] range
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                          int use_quality_100, VP8LBitWriter* const bw,
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0
                          WebPAuxStats* const stats) {
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0
  int ok = 0;
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0
  WebPConfig config;
57
0
  WebPPicture picture;
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59
0
  if (!WebPPictureInit(&picture)) return 0;
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0
  picture.width = width;
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0
  picture.height = height;
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0
  picture.use_argb = 1;
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0
  picture.stats = stats;
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0
  if (!WebPPictureAlloc(&picture)) return 0;
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  // Transfer the alpha values to the green channel.
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0
  WebPDispatchAlphaToGreen(data, width, picture.width, picture.height,
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0
                           picture.argb, picture.argb_stride);
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70
0
  if (!WebPConfigInit(&config)) return 0;
71
0
  config.lossless = 1;
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  // Enable exact, or it would alter RGB values of transparent alpha, which is
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  // normally OK but not here since we are not encoding the input image but  an
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  // internal encoding-related image containing necessary exact information in
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  // RGB channels.
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0
  config.exact = 1;
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0
  config.method = effort_level;  // impact is very small
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  // Set a low default quality for encoding alpha. Ensure that Alpha quality at
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  // lower methods (3 and below) is less than the threshold for triggering
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  // costly 'BackwardReferencesTraceBackwards'.
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  // If the alpha quality is set to 100 and the method to 6, allow for a high
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  // lossless quality to trigger the cruncher.
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0
  config.quality =
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0
      (use_quality_100 && effort_level == 6) ? 100 : 8.f * effort_level;
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0
  assert(config.quality >= 0 && config.quality <= 100.f);
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  ok = VP8LEncodeStream(&config, &picture, bw);
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0
  WebPPictureFree(&picture);
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0
  ok = ok && !bw->error_;
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0
  if (!ok) {
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0
    VP8LBitWriterWipeOut(bw);
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0
    return 0;
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0
  }
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0
  return 1;
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0
}
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// -----------------------------------------------------------------------------
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// Small struct to hold the result of a filter mode compression attempt.
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typedef struct {
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  size_t score;
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  VP8BitWriter bw;
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  WebPAuxStats stats;
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} FilterTrial;
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// This function always returns an initialized 'bw' object, even upon error.
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static int EncodeAlphaInternal(const uint8_t* const data, int width, int height,
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                               int method, int filter, int reduce_levels,
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                               int effort_level,  // in [0..6] range
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                               uint8_t* const tmp_alpha,
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0
                               FilterTrial* result) {
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0
  int ok = 0;
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0
  const uint8_t* alpha_src;
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0
  WebPFilterFunc filter_func;
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0
  uint8_t header;
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0
  const size_t data_size = width * height;
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0
  const uint8_t* output = NULL;
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0
  size_t output_size = 0;
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0
  VP8LBitWriter tmp_bw;
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121
0
  assert((uint64_t)data_size == (uint64_t)width * height);  // as per spec
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  assert(filter >= 0 && filter < WEBP_FILTER_LAST);
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0
  assert(method >= ALPHA_NO_COMPRESSION);
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0
  assert(method <= ALPHA_LOSSLESS_COMPRESSION);
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0
  assert(sizeof(header) == ALPHA_HEADER_LEN);
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127
0
  filter_func = WebPFilters[filter];
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0
  if (filter_func != NULL) {
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0
    filter_func(data, width, height, width, tmp_alpha);
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0
    alpha_src = tmp_alpha;
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0
  }  else {
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    alpha_src = data;
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0
  }
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0
  if (method != ALPHA_NO_COMPRESSION) {
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    ok = VP8LBitWriterInit(&tmp_bw, data_size >> 3);
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0
    ok = ok && EncodeLossless(alpha_src, width, height, effort_level,
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0
                              !reduce_levels, &tmp_bw, &result->stats);
139
0
    if (ok) {
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0
      output = VP8LBitWriterFinish(&tmp_bw);
141
0
      if (tmp_bw.error_) {
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0
        VP8LBitWriterWipeOut(&tmp_bw);
143
0
        memset(&result->bw, 0, sizeof(result->bw));
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0
        return 0;
145
0
      }
146
0
      output_size = VP8LBitWriterNumBytes(&tmp_bw);
147
0
      if (output_size > data_size) {
148
        // compressed size is larger than source! Revert to uncompressed mode.
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0
        method = ALPHA_NO_COMPRESSION;
150
0
        VP8LBitWriterWipeOut(&tmp_bw);
151
0
      }
152
0
    } else {
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0
      VP8LBitWriterWipeOut(&tmp_bw);
154
0
      memset(&result->bw, 0, sizeof(result->bw));
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0
      return 0;
156
0
    }
157
0
  }
158
159
0
  if (method == ALPHA_NO_COMPRESSION) {
160
0
    output = alpha_src;
161
0
    output_size = data_size;
162
0
    ok = 1;
163
0
  }
164
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  // Emit final result.
166
0
  header = method | (filter << 2);
167
0
  if (reduce_levels) header |= ALPHA_PREPROCESSED_LEVELS << 4;
168
169
0
  if (!VP8BitWriterInit(&result->bw, ALPHA_HEADER_LEN + output_size)) ok = 0;
170
0
  ok = ok && VP8BitWriterAppend(&result->bw, &header, ALPHA_HEADER_LEN);
171
0
  ok = ok && VP8BitWriterAppend(&result->bw, output, output_size);
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173
0
  if (method != ALPHA_NO_COMPRESSION) {
174
0
    VP8LBitWriterWipeOut(&tmp_bw);
175
0
  }
176
0
  ok = ok && !result->bw.error_;
177
0
  result->score = VP8BitWriterSize(&result->bw);
178
0
  return ok;
179
0
}
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// -----------------------------------------------------------------------------
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183
static int GetNumColors(const uint8_t* data, int width, int height,
184
0
                        int stride) {
185
0
  int j;
186
0
  int colors = 0;
187
0
  uint8_t color[256] = { 0 };
188
189
0
  for (j = 0; j < height; ++j) {
190
0
    int i;
191
0
    const uint8_t* const p = data + j * stride;
192
0
    for (i = 0; i < width; ++i) {
193
0
      color[p[i]] = 1;
194
0
    }
195
0
  }
196
0
  for (j = 0; j < 256; ++j) {
197
0
    if (color[j] > 0) ++colors;
198
0
  }
199
0
  return colors;
200
0
}
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202
0
#define FILTER_TRY_NONE (1 << WEBP_FILTER_NONE)
203
0
#define FILTER_TRY_ALL ((1 << WEBP_FILTER_LAST) - 1)
204
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// Given the input 'filter' option, return an OR'd bit-set of filters to try.
206
static uint32_t GetFilterMap(const uint8_t* alpha, int width, int height,
207
0
                             int filter, int effort_level) {
208
0
  uint32_t bit_map = 0U;
209
0
  if (filter == WEBP_FILTER_FAST) {
210
    // Quick estimate of the best candidate.
211
0
    int try_filter_none = (effort_level > 3);
212
0
    const int kMinColorsForFilterNone = 16;
213
0
    const int kMaxColorsForFilterNone = 192;
214
0
    const int num_colors = GetNumColors(alpha, width, height, width);
215
    // For low number of colors, NONE yields better compression.
216
0
    filter = (num_colors <= kMinColorsForFilterNone)
217
0
        ? WEBP_FILTER_NONE
218
0
        : WebPEstimateBestFilter(alpha, width, height, width);
219
0
    bit_map |= 1 << filter;
220
    // For large number of colors, try FILTER_NONE in addition to the best
221
    // filter as well.
222
0
    if (try_filter_none || num_colors > kMaxColorsForFilterNone) {
223
0
      bit_map |= FILTER_TRY_NONE;
224
0
    }
225
0
  } else if (filter == WEBP_FILTER_NONE) {
226
0
    bit_map = FILTER_TRY_NONE;
227
0
  } else {  // WEBP_FILTER_BEST -> try all
228
0
    bit_map = FILTER_TRY_ALL;
229
0
  }
230
0
  return bit_map;
231
0
}
232
233
0
static void InitFilterTrial(FilterTrial* const score) {
234
0
  score->score = (size_t)~0U;
235
0
  VP8BitWriterInit(&score->bw, 0);
236
0
}
237
238
static int ApplyFiltersAndEncode(const uint8_t* alpha, int width, int height,
239
                                 size_t data_size, int method, int filter,
240
                                 int reduce_levels, int effort_level,
241
                                 uint8_t** const output,
242
                                 size_t* const output_size,
243
0
                                 WebPAuxStats* const stats) {
244
0
  int ok = 1;
245
0
  FilterTrial best;
246
0
  uint32_t try_map =
247
0
      GetFilterMap(alpha, width, height, filter, effort_level);
248
0
  InitFilterTrial(&best);
249
250
0
  if (try_map != FILTER_TRY_NONE) {
251
0
    uint8_t* filtered_alpha =  (uint8_t*)WebPSafeMalloc(1ULL, data_size);
252
0
    if (filtered_alpha == NULL) return 0;
253
254
0
    for (filter = WEBP_FILTER_NONE; ok && try_map; ++filter, try_map >>= 1) {
255
0
      if (try_map & 1) {
256
0
        FilterTrial trial;
257
0
        ok = EncodeAlphaInternal(alpha, width, height, method, filter,
258
0
                                 reduce_levels, effort_level, filtered_alpha,
259
0
                                 &trial);
260
0
        if (ok && trial.score < best.score) {
261
0
          VP8BitWriterWipeOut(&best.bw);
262
0
          best = trial;
263
0
        } else {
264
0
          VP8BitWriterWipeOut(&trial.bw);
265
0
        }
266
0
      }
267
0
    }
268
0
    WebPSafeFree(filtered_alpha);
269
0
  } else {
270
0
    ok = EncodeAlphaInternal(alpha, width, height, method, WEBP_FILTER_NONE,
271
0
                             reduce_levels, effort_level, NULL, &best);
272
0
  }
273
0
  if (ok) {
274
0
#if !defined(WEBP_DISABLE_STATS)
275
0
    if (stats != NULL) {
276
0
      stats->lossless_features = best.stats.lossless_features;
277
0
      stats->histogram_bits = best.stats.histogram_bits;
278
0
      stats->transform_bits = best.stats.transform_bits;
279
0
      stats->cross_color_transform_bits = best.stats.cross_color_transform_bits;
280
0
      stats->cache_bits = best.stats.cache_bits;
281
0
      stats->palette_size = best.stats.palette_size;
282
0
      stats->lossless_size = best.stats.lossless_size;
283
0
      stats->lossless_hdr_size = best.stats.lossless_hdr_size;
284
0
      stats->lossless_data_size = best.stats.lossless_data_size;
285
0
    }
286
#else
287
    (void)stats;
288
#endif
289
0
    *output_size = VP8BitWriterSize(&best.bw);
290
0
    *output = VP8BitWriterBuf(&best.bw);
291
0
  } else {
292
0
    VP8BitWriterWipeOut(&best.bw);
293
0
  }
294
0
  return ok;
295
0
}
296
297
static int EncodeAlpha(VP8Encoder* const enc,
298
                       int quality, int method, int filter,
299
                       int effort_level,
300
0
                       uint8_t** const output, size_t* const output_size) {
301
0
  const WebPPicture* const pic = enc->pic_;
302
0
  const int width = pic->width;
303
0
  const int height = pic->height;
304
305
0
  uint8_t* quant_alpha = NULL;
306
0
  const size_t data_size = width * height;
307
0
  uint64_t sse = 0;
308
0
  int ok = 1;
309
0
  const int reduce_levels = (quality < 100);
310
311
  // quick correctness checks
312
0
  assert((uint64_t)data_size == (uint64_t)width * height);  // as per spec
313
0
  assert(enc != NULL && pic != NULL && pic->a != NULL);
314
0
  assert(output != NULL && output_size != NULL);
315
0
  assert(width > 0 && height > 0);
316
0
  assert(pic->a_stride >= width);
317
0
  assert(filter >= WEBP_FILTER_NONE && filter <= WEBP_FILTER_FAST);
318
319
0
  if (quality < 0 || quality > 100) {
320
0
    return WebPEncodingSetError(pic, VP8_ENC_ERROR_INVALID_CONFIGURATION);
321
0
  }
322
323
0
  if (method < ALPHA_NO_COMPRESSION || method > ALPHA_LOSSLESS_COMPRESSION) {
324
0
    return WebPEncodingSetError(pic, VP8_ENC_ERROR_INVALID_CONFIGURATION);
325
0
  }
326
327
0
  if (method == ALPHA_NO_COMPRESSION) {
328
    // Don't filter, as filtering will make no impact on compressed size.
329
0
    filter = WEBP_FILTER_NONE;
330
0
  }
331
332
0
  quant_alpha = (uint8_t*)WebPSafeMalloc(1ULL, data_size);
333
0
  if (quant_alpha == NULL) {
334
0
    return WebPEncodingSetError(pic, VP8_ENC_ERROR_OUT_OF_MEMORY);
335
0
  }
336
337
  // Extract alpha data (width x height) from raw_data (stride x height).
338
0
  WebPCopyPlane(pic->a, pic->a_stride, quant_alpha, width, width, height);
339
340
0
  if (reduce_levels) {  // No Quantization required for 'quality = 100'.
341
    // 16 alpha levels gives quite a low MSE w.r.t original alpha plane hence
342
    // mapped to moderate quality 70. Hence Quality:[0, 70] -> Levels:[2, 16]
343
    // and Quality:]70, 100] -> Levels:]16, 256].
344
0
    const int alpha_levels = (quality <= 70) ? (2 + quality / 5)
345
0
                                             : (16 + (quality - 70) * 8);
346
0
    ok = QuantizeLevels(quant_alpha, width, height, alpha_levels, &sse);
347
0
  }
348
349
0
  if (ok) {
350
0
    VP8FiltersInit();
351
0
    ok = ApplyFiltersAndEncode(quant_alpha, width, height, data_size, method,
352
0
                               filter, reduce_levels, effort_level, output,
353
0
                               output_size, pic->stats);
354
0
    if (!ok) {
355
0
      WebPEncodingSetError(pic, VP8_ENC_ERROR_OUT_OF_MEMORY);  // imprecise
356
0
    }
357
0
#if !defined(WEBP_DISABLE_STATS)
358
0
    if (pic->stats != NULL) {  // need stats?
359
0
      pic->stats->coded_size += (int)(*output_size);
360
0
      enc->sse_[3] = sse;
361
0
    }
362
0
#endif
363
0
  }
364
365
0
  WebPSafeFree(quant_alpha);
366
0
  return ok;
367
0
}
368
369
//------------------------------------------------------------------------------
370
// Main calls
371
372
0
static int CompressAlphaJob(void* arg1, void* unused) {
373
0
  VP8Encoder* const enc = (VP8Encoder*)arg1;
374
0
  const WebPConfig* config = enc->config_;
375
0
  uint8_t* alpha_data = NULL;
376
0
  size_t alpha_size = 0;
377
0
  const int effort_level = config->method;  // maps to [0..6]
378
0
  const WEBP_FILTER_TYPE filter =
379
0
      (config->alpha_filtering == 0) ? WEBP_FILTER_NONE :
380
0
      (config->alpha_filtering == 1) ? WEBP_FILTER_FAST :
381
0
                                       WEBP_FILTER_BEST;
382
0
  if (!EncodeAlpha(enc, config->alpha_quality, config->alpha_compression,
383
0
                   filter, effort_level, &alpha_data, &alpha_size)) {
384
0
    return 0;
385
0
  }
386
0
  if (alpha_size != (uint32_t)alpha_size) {  // Soundness check.
387
0
    WebPSafeFree(alpha_data);
388
0
    return 0;
389
0
  }
390
0
  enc->alpha_data_size_ = (uint32_t)alpha_size;
391
0
  enc->alpha_data_ = alpha_data;
392
0
  (void)unused;
393
0
  return 1;
394
0
}
395
396
0
void VP8EncInitAlpha(VP8Encoder* const enc) {
397
0
  WebPInitAlphaProcessing();
398
0
  enc->has_alpha_ = WebPPictureHasTransparency(enc->pic_);
399
0
  enc->alpha_data_ = NULL;
400
0
  enc->alpha_data_size_ = 0;
401
0
  if (enc->thread_level_ > 0) {
402
0
    WebPWorker* const worker = &enc->alpha_worker_;
403
0
    WebPGetWorkerInterface()->Init(worker);
404
0
    worker->data1 = enc;
405
0
    worker->data2 = NULL;
406
0
    worker->hook = CompressAlphaJob;
407
0
  }
408
0
}
409
410
0
int VP8EncStartAlpha(VP8Encoder* const enc) {
411
0
  if (enc->has_alpha_) {
412
0
    if (enc->thread_level_ > 0) {
413
0
      WebPWorker* const worker = &enc->alpha_worker_;
414
      // Makes sure worker is good to go.
415
0
      if (!WebPGetWorkerInterface()->Reset(worker)) {
416
0
        return WebPEncodingSetError(enc->pic_, VP8_ENC_ERROR_OUT_OF_MEMORY);
417
0
      }
418
0
      WebPGetWorkerInterface()->Launch(worker);
419
0
      return 1;
420
0
    } else {
421
0
      return CompressAlphaJob(enc, NULL);   // just do the job right away
422
0
    }
423
0
  }
424
0
  return 1;
425
0
}
426
427
0
int VP8EncFinishAlpha(VP8Encoder* const enc) {
428
0
  if (enc->has_alpha_) {
429
0
    if (enc->thread_level_ > 0) {
430
0
      WebPWorker* const worker = &enc->alpha_worker_;
431
0
      if (!WebPGetWorkerInterface()->Sync(worker)) return 0;  // error
432
0
    }
433
0
  }
434
0
  return WebPReportProgress(enc->pic_, enc->percent_ + 20, &enc->percent_);
435
0
}
436
437
0
int VP8EncDeleteAlpha(VP8Encoder* const enc) {
438
0
  int ok = 1;
439
0
  if (enc->thread_level_ > 0) {
440
0
    WebPWorker* const worker = &enc->alpha_worker_;
441
    // finish anything left in flight
442
0
    ok = WebPGetWorkerInterface()->Sync(worker);
443
    // still need to end the worker, even if !ok
444
0
    WebPGetWorkerInterface()->End(worker);
445
0
  }
446
0
  WebPSafeFree(enc->alpha_data_);
447
0
  enc->alpha_data_ = NULL;
448
0
  enc->alpha_data_size_ = 0;
449
0
  enc->has_alpha_ = 0;
450
0
  return ok;
451
0
}