int VP8EncTokenLoop()

in Extended/libwebp/src/enc/frame_enc.c [774:879]

• 99 lines of code
• 23 McCabe index (conditional complexity)

int VP8EncTokenLoop(VP8Encoder* const enc) {
  // Roughly refresh the proba eight times per pass
  int max_count = (enc->mb_w_ * enc->mb_h_) >> 3;
  int num_pass_left = enc->config_->pass;
  const int do_search = enc->do_search_;
  VP8EncIterator it;
  VP8EncProba* const proba = &enc->proba_;
  const VP8RDLevel rd_opt = enc->rd_opt_level_;
  const uint64_t pixel_count = enc->mb_w_ * enc->mb_h_ * 384;
  PassStats stats;
  int ok;

  InitPassStats(enc, &stats);
  ok = PreLoopInitialize(enc);
  if (!ok) return 0;

  if (max_count < MIN_COUNT) max_count = MIN_COUNT;

  assert(enc->num_parts_ == 1);
  assert(enc->use_tokens_);
  assert(proba->use_skip_proba_ == 0);
  assert(rd_opt >= RD_OPT_BASIC);   // otherwise, token-buffer won't be useful
  assert(num_pass_left > 0);

  while (ok && num_pass_left-- > 0) {
    const int is_last_pass = (fabs(stats.dq) <= DQ_LIMIT) ||
                             (num_pass_left == 0) ||
                             (enc->max_i4_header_bits_ == 0);
    uint64_t size_p0 = 0;
    uint64_t distortion = 0;
    int cnt = max_count;
    VP8IteratorInit(enc, &it);
    SetLoopParams(enc, stats.q);
    if (is_last_pass) {
      ResetTokenStats(enc);
      VP8InitFilter(&it);  // don't collect stats until last pass (too costly)
    }
    VP8TBufferClear(&enc->tokens_);
    do {
      VP8ModeScore info;
      VP8IteratorImport(&it, NULL);
      if (--cnt < 0) {
        FinalizeTokenProbas(proba);
        VP8CalculateLevelCosts(proba);  // refresh cost tables for rd-opt
        cnt = max_count;
      }
      VP8Decimate(&it, &info, rd_opt);
      ok = RecordTokens(&it, &info, &enc->tokens_);
      if (!ok) {
        WebPEncodingSetError(enc->pic_, VP8_ENC_ERROR_OUT_OF_MEMORY);
        break;
      }
      size_p0 += info.H;
      distortion += info.D;
      if (is_last_pass) {
        StoreSideInfo(&it);
        VP8StoreFilterStats(&it);
        VP8IteratorExport(&it);
        ok = VP8IteratorProgress(&it, 20);
      }
      VP8IteratorSaveBoundary(&it);
    } while (ok && VP8IteratorNext(&it));
    if (!ok) break;

    size_p0 += enc->segment_hdr_.size_;
    if (stats.do_size_search) {
      uint64_t size = FinalizeTokenProbas(&enc->proba_);
      size += VP8EstimateTokenSize(&enc->tokens_,
                                   (const uint8_t*)proba->coeffs_);
      size = (size + size_p0 + 1024) >> 11;  // -> size in bytes
      size += HEADER_SIZE_ESTIMATE;
      stats.value = (double)size;
    } else {  // compute and store PSNR
      stats.value = GetPSNR(distortion, pixel_count);
    }

#if (DEBUG_SEARCH > 0)
    printf("#%2d metric:%.1lf -> %.1lf   last_q=%.2lf q=%.2lf dq=%.2lf\n",
           num_pass_left, stats.last_value, stats.value,
           stats.last_q, stats.q, stats.dq);
#endif
    if (enc->max_i4_header_bits_ > 0 && size_p0 > PARTITION0_SIZE_LIMIT) {
      ++num_pass_left;
      enc->max_i4_header_bits_ >>= 1;  // strengthen header bit limitation...
      if (is_last_pass) {
        ResetSideInfo(&it);
      }
      continue;                        // ...and start over
    }
    if (is_last_pass) {
      break;   // done
    }
    if (do_search) {
      ComputeNextQ(&stats);  // Adjust q
    }
  }
  if (ok) {
    if (!stats.do_size_search) {
      FinalizeTokenProbas(&enc->proba_);
    }
    ok = VP8EmitTokens(&enc->tokens_, enc->parts_ + 0,
                       (const uint8_t*)proba->coeffs_, 1);
  }
  ok = ok && WebPReportProgress(enc->pic_, enc->percent_ + 20, &enc->percent_);
  return PostLoopFinalize(&it, ok);
}