third_party/libwebp/dec/vp8.c

   1 // Copyright 2010 Google Inc. All Rights Reserved.
   2 //
   3 // Use of this source code is governed by a BSD-style license
   4 // that can be found in the COPYING file in the root of the source
   5 // tree. An additional intellectual property rights grant can be found
   6 // in the file PATENTS. All contributing project authors may
   7 // be found in the AUTHORS file in the root of the source tree.
   8 // -----------------------------------------------------------------------------
   9 //
  10 // main entry for the decoder
  11 //
  12 // Author: Skal (pascal.massimino@gmail.com)
  13
  14 #include <stdlib.h>
  15
  16 #include "./alphai.h"
  17 #include "./vp8i.h"
  18 #include "./vp8li.h"
  19 #include "./webpi.h"
  20 #include "../utils/bit_reader_inl.h"
  21 #include "../utils/utils.h"
  22
  23 //------------------------------------------------------------------------------
  24
  25 int WebPGetDecoderVersion(void) {
  26   return (DEC_MAJ_VERSION << 16) | (DEC_MIN_VERSION << 8) | DEC_REV_VERSION;
  27 }
  28
  29 //------------------------------------------------------------------------------
  30 // VP8Decoder
  31
  32 static void SetOk(VP8Decoder* const dec) {
  33   dec->status_ = VP8_STATUS_OK;
  34   dec->error_msg_ = "OK";
  35 }
  36
  37 int VP8InitIoInternal(VP8Io* const io, int version) {
  38   if (WEBP_ABI_IS_INCOMPATIBLE(version, WEBP_DECODER_ABI_VERSION)) {
  39     return 0;  // mismatch error
  40   }
  41   if (io != NULL) {
  42     memset(io, 0, sizeof(*io));
  43   }
  44   return 1;
  45 }
  46
  47 VP8Decoder* VP8New(void) {
  48   VP8Decoder* const dec = (VP8Decoder*)WebPSafeCalloc(1ULL, sizeof(*dec));
  49   if (dec != NULL) {
  50     SetOk(dec);
  51     WebPGetWorkerInterface()->Init(&dec->worker_);
  52     dec->ready_ = 0;
  53     dec->num_parts_ = 1;
  54   }
  55   return dec;
  56 }
  57
  58 VP8StatusCode VP8Status(VP8Decoder* const dec) {
  59   if (!dec) return VP8_STATUS_INVALID_PARAM;
  60   return dec->status_;
  61 }
  62
  63 const char* VP8StatusMessage(VP8Decoder* const dec) {
  64   if (dec == NULL) return "no object";
  65   if (!dec->error_msg_) return "OK";
  66   return dec->error_msg_;
  67 }
  68
  69 void VP8Delete(VP8Decoder* const dec) {
  70   if (dec != NULL) {
  71     VP8Clear(dec);
  72     WebPSafeFree(dec);
  73   }
  74 }
  75
  76 int VP8SetError(VP8Decoder* const dec,
  77                 VP8StatusCode error, const char* const msg) {
  78   // TODO This check would be unnecessary if alpha decompression was separated
  79   // from VP8ProcessRow/FinishRow. This avoids setting 'dec->status_' to
  80   // something other than VP8_STATUS_BITSTREAM_ERROR on alpha decompression
  81   // failure.
  82   if (dec->status_ == VP8_STATUS_OK) {
  83     dec->status_ = error;
  84     dec->error_msg_ = msg;
  85     dec->ready_ = 0;
  86   }
  87   return 0;
  88 }
  89
  90 //------------------------------------------------------------------------------
  91
  92 int VP8CheckSignature(const uint8_t* const data, size_t data_size) {
  93   return (data_size >= 3 &&
  94           data[0] == 0x9d && data[1] == 0x01 && data[2] == 0x2a);
  95 }
  96
  97 int VP8GetInfo(const uint8_t* data, size_t data_size, size_t chunk_size,
  98                int* const width, int* const height) {
  99   if (data == NULL || data_size < VP8_FRAME_HEADER_SIZE) {
 100     return 0;         // not enough data
 101   }
 102   // check signature
 103   if (!VP8CheckSignature(data + 3, data_size - 3)) {
 104     return 0;         // Wrong signature.
 105   } else {
 106     const uint32_t bits = data[0] | (data[1] << 8) | (data[2] << 16);
 107     const int key_frame = !(bits & 1);
 108     const int w = ((data[7] << 8) | data[6]) & 0x3fff;
 109     const int h = ((data[9] << 8) | data[8]) & 0x3fff;
 110
 111     if (!key_frame) {   // Not a keyframe.
 112       return 0;
 113     }
 114
 115     if (((bits >> 1) & 7) > 3) {
 116       return 0;         // unknown profile
 117     }
 118     if (!((bits >> 4) & 1)) {
 119       return 0;         // first frame is invisible!
 120     }
 121     if (((bits >> 5)) >= chunk_size) {  // partition_length
 122       return 0;         // inconsistent size information.
 123     }
 124     if (w == 0 || h == 0) {
 125       return 0;         // We don't support both width and height to be zero.
 126     }
 127
 128     if (width) {
 129       *width = w;
 130     }
 131     if (height) {
 132       *height = h;
 133     }
 134
 135     return 1;
 136   }
 137 }
 138
 139 //------------------------------------------------------------------------------
 140 // Header parsing
 141
 142 static void ResetSegmentHeader(VP8SegmentHeader* const hdr) {
 143   assert(hdr != NULL);
 144   hdr->use_segment_ = 0;
 145   hdr->update_map_ = 0;
 146   hdr->absolute_delta_ = 1;
 147   memset(hdr->quantizer_, 0, sizeof(hdr->quantizer_));
 148   memset(hdr->filter_strength_, 0, sizeof(hdr->filter_strength_));
 149 }
 150
 151 // Paragraph 9.3
 152 static int ParseSegmentHeader(VP8BitReader* br,
 153                               VP8SegmentHeader* hdr, VP8Proba* proba) {
 154   assert(br != NULL);
 155   assert(hdr != NULL);
 156   hdr->use_segment_ = VP8Get(br);
 157   if (hdr->use_segment_) {
 158     hdr->update_map_ = VP8Get(br);
 159     if (VP8Get(br)) {   // update data
 160       int s;
 161       hdr->absolute_delta_ = VP8Get(br);
 162       for (s = 0; s < NUM_MB_SEGMENTS; ++s) {
 163         hdr->quantizer_[s] = VP8Get(br) ? VP8GetSignedValue(br, 7) : 0;
 164       }
 165       for (s = 0; s < NUM_MB_SEGMENTS; ++s) {
 166         hdr->filter_strength_[s] = VP8Get(br) ? VP8GetSignedValue(br, 6) : 0;
 167       }
 168     }
 169     if (hdr->update_map_) {
 170       int s;
 171       for (s = 0; s < MB_FEATURE_TREE_PROBS; ++s) {
 172         proba->segments_[s] = VP8Get(br) ? VP8GetValue(br, 8) : 255u;
 173       }
 174     }
 175   } else {
 176     hdr->update_map_ = 0;
 177   }
 178   return !br->eof_;
 179 }
 180
 181 // Paragraph 9.5
 182 // This function returns VP8_STATUS_SUSPENDED if we don't have all the
 183 // necessary data in 'buf'.
 184 // This case is not necessarily an error (for incremental decoding).
 185 // Still, no bitreader is ever initialized to make it possible to read
 186 // unavailable memory.
 187 // If we don't even have the partitions' sizes, than VP8_STATUS_NOT_ENOUGH_DATA
 188 // is returned, and this is an unrecoverable error.
 189 // If the partitions were positioned ok, VP8_STATUS_OK is returned.
 190 static VP8StatusCode ParsePartitions(VP8Decoder* const dec,
 191                                      const uint8_t* buf, size_t size) {
 192   VP8BitReader* const br = &dec->br_;
 193   const uint8_t* sz = buf;
 194   const uint8_t* buf_end = buf + size;
 195   const uint8_t* part_start;
 196   int last_part;
 197   int p;
 198
 199   dec->num_parts_ = 1 << VP8GetValue(br, 2);
 200   last_part = dec->num_parts_ - 1;
 201   part_start = buf + last_part * 3;
 202   if (buf_end < part_start) {
 203     // we can't even read the sizes with sz[]! That's a failure.
 204     return VP8_STATUS_NOT_ENOUGH_DATA;
 205   }
 206   for (p = 0; p < last_part; ++p) {
 207     const uint32_t psize = sz[0] | (sz[1] << 8) | (sz[2] << 16);
 208     const uint8_t* part_end = part_start + psize;
 209     if (part_end > buf_end) part_end = buf_end;
 210     VP8InitBitReader(dec->parts_ + p, part_start, part_end);
 211     part_start = part_end;
 212     sz += 3;
 213   }
 214   VP8InitBitReader(dec->parts_ + last_part, part_start, buf_end);
 215   return (part_start < buf_end) ? VP8_STATUS_OK :
 216            VP8_STATUS_SUSPENDED;   // Init is ok, but there's not enough data
 217 }
 218
 219 // Paragraph 9.4
 220 static int ParseFilterHeader(VP8BitReader* br, VP8Decoder* const dec) {
 221   VP8FilterHeader* const hdr = &dec->filter_hdr_;
 222   hdr->simple_    = VP8Get(br);
 223   hdr->level_     = VP8GetValue(br, 6);
 224   hdr->sharpness_ = VP8GetValue(br, 3);
 225   hdr->use_lf_delta_ = VP8Get(br);
 226   if (hdr->use_lf_delta_) {
 227     if (VP8Get(br)) {   // update lf-delta?
 228       int i;
 229       for (i = 0; i < NUM_REF_LF_DELTAS; ++i) {
 230         if (VP8Get(br)) {
 231           hdr->ref_lf_delta_[i] = VP8GetSignedValue(br, 6);
 232         }
 233       }
 234       for (i = 0; i < NUM_MODE_LF_DELTAS; ++i) {
 235         if (VP8Get(br)) {
 236           hdr->mode_lf_delta_[i] = VP8GetSignedValue(br, 6);
 237         }
 238       }
 239     }
 240   }
 241   dec->filter_type_ = (hdr->level_ == 0) ? 0 : hdr->simple_ ? 1 : 2;
 242   return !br->eof_;
 243 }
 244
 245 // Topmost call
 246 int VP8GetHeaders(VP8Decoder* const dec, VP8Io* const io) {
 247   const uint8_t* buf;
 248   size_t buf_size;
 249   VP8FrameHeader* frm_hdr;
 250   VP8PictureHeader* pic_hdr;
 251   VP8BitReader* br;
 252   VP8StatusCode status;
 253
 254   if (dec == NULL) {
 255     return 0;
 256   }
 257   SetOk(dec);
 258   if (io == NULL) {
 259     return VP8SetError(dec, VP8_STATUS_INVALID_PARAM,
 260                        "null VP8Io passed to VP8GetHeaders()");
 261   }
 262   buf = io->data;
 263   buf_size = io->data_size;
 264   if (buf_size < 4) {
 265     return VP8SetError(dec, VP8_STATUS_NOT_ENOUGH_DATA,
 266                        "Truncated header.");
 267   }
 268
 269   // Paragraph 9.1
 270   {
 271     const uint32_t bits = buf[0] | (buf[1] << 8) | (buf[2] << 16);
 272     frm_hdr = &dec->frm_hdr_;
 273     frm_hdr->key_frame_ = !(bits & 1);
 274     frm_hdr->profile_ = (bits >> 1) & 7;
 275     frm_hdr->show_ = (bits >> 4) & 1;
 276     frm_hdr->partition_length_ = (bits >> 5);
 277     if (frm_hdr->profile_ > 3)
 278       return VP8SetError(dec, VP8_STATUS_BITSTREAM_ERROR,
 279                          "Incorrect keyframe parameters.");
 280     if (!frm_hdr->show_)
 281       return VP8SetError(dec, VP8_STATUS_UNSUPPORTED_FEATURE,
 282                          "Frame not displayable.");
 283     buf += 3;
 284     buf_size -= 3;
 285   }
 286
 287   pic_hdr = &dec->pic_hdr_;
 288   if (frm_hdr->key_frame_) {
 289     // Paragraph 9.2
 290     if (buf_size < 7) {
 291       return VP8SetError(dec, VP8_STATUS_NOT_ENOUGH_DATA,
 292                          "cannot parse picture header");
 293     }
 294     if (!VP8CheckSignature(buf, buf_size)) {
 295       return VP8SetError(dec, VP8_STATUS_BITSTREAM_ERROR,
 296                          "Bad code word");
 297     }
 298     pic_hdr->width_ = ((buf[4] << 8) | buf[3]) & 0x3fff;
 299     pic_hdr->xscale_ = buf[4] >> 6;   // ratio: 1, 5/4 5/3 or 2
 300     pic_hdr->height_ = ((buf[6] << 8) | buf[5]) & 0x3fff;
 301     pic_hdr->yscale_ = buf[6] >> 6;
 302     buf += 7;
 303     buf_size -= 7;
 304
 305     dec->mb_w_ = (pic_hdr->width_ + 15) >> 4;
 306     dec->mb_h_ = (pic_hdr->height_ + 15) >> 4;
 307     // Setup default output area (can be later modified during io->setup())
 308     io->width = pic_hdr->width_;
 309     io->height = pic_hdr->height_;
 310     io->use_scaling  = 0;
 311     io->use_cropping = 0;
 312     io->crop_top  = 0;
 313     io->crop_left = 0;
 314     io->crop_right  = io->width;
 315     io->crop_bottom = io->height;
 316     io->mb_w = io->width;   // sanity check
 317     io->mb_h = io->height;  // ditto
 318
 319     VP8ResetProba(&dec->proba_);
 320     ResetSegmentHeader(&dec->segment_hdr_);
 321   }
 322
 323   // Check if we have all the partition #0 available, and initialize dec->br_
 324   // to read this partition (and this partition only).
 325   if (frm_hdr->partition_length_ > buf_size) {
 326     return VP8SetError(dec, VP8_STATUS_NOT_ENOUGH_DATA,
 327                        "bad partition length");
 328   }
 329
 330   br = &dec->br_;
 331   VP8InitBitReader(br, buf, buf + frm_hdr->partition_length_);
 332   buf += frm_hdr->partition_length_;
 333   buf_size -= frm_hdr->partition_length_;
 334
 335   if (frm_hdr->key_frame_) {
 336     pic_hdr->colorspace_ = VP8Get(br);
 337     pic_hdr->clamp_type_ = VP8Get(br);
 338   }
 339   if (!ParseSegmentHeader(br, &dec->segment_hdr_, &dec->proba_)) {
 340     return VP8SetError(dec, VP8_STATUS_BITSTREAM_ERROR,
 341                        "cannot parse segment header");
 342   }
 343   // Filter specs
 344   if (!ParseFilterHeader(br, dec)) {
 345     return VP8SetError(dec, VP8_STATUS_BITSTREAM_ERROR,
 346                        "cannot parse filter header");
 347   }
 348   status = ParsePartitions(dec, buf, buf_size);
 349   if (status != VP8_STATUS_OK) {
 350     return VP8SetError(dec, status, "cannot parse partitions");
 351   }
 352
 353   // quantizer change
 354   VP8ParseQuant(dec);
 355
 356   // Frame buffer marking
 357   if (!frm_hdr->key_frame_) {
 358     return VP8SetError(dec, VP8_STATUS_UNSUPPORTED_FEATURE,
 359                        "Not a key frame.");
 360   }
 361
 362   VP8Get(br);   // ignore the value of update_proba_
 363
 364   VP8ParseProba(br, dec);
 365
 366   // sanitized state
 367   dec->ready_ = 1;
 368   return 1;
 369 }
 370
 371 //------------------------------------------------------------------------------
 372 // Residual decoding (Paragraph 13.2 / 13.3)
 373
 374 static const int kBands[16 + 1] = {
 375   0, 1, 2, 3, 6, 4, 5, 6, 6, 6, 6, 6, 6, 6, 6, 7,
 376   0  // extra entry as sentinel
 377 };
 378
 379 static const uint8_t kCat3[] = { 173, 148, 140, 0 };
 380 static const uint8_t kCat4[] = { 176, 155, 140, 135, 0 };
 381 static const uint8_t kCat5[] = { 180, 157, 141, 134, 130, 0 };
 382 static const uint8_t kCat6[] =
 383   { 254, 254, 243, 230, 196, 177, 153, 140, 133, 130, 129, 0 };
 384 static const uint8_t* const kCat3456[] = { kCat3, kCat4, kCat5, kCat6 };
 385 static const uint8_t kZigzag[16] = {
 386   0, 1, 4, 8,  5, 2, 3, 6,  9, 12, 13, 10,  7, 11, 14, 15
 387 };
 388
 389 // See section 13-2: http://tools.ietf.org/html/rfc6386#section-13.2
 390 static int GetLargeValue(VP8BitReader* const br, const uint8_t* const p) {
 391   int v;
 392   if (!VP8GetBit(br, p[3])) {
 393     if (!VP8GetBit(br, p[4])) {
 394       v = 2;
 395     } else {
 396       v = 3 + VP8GetBit(br, p[5]);
 397     }
 398   } else {
 399     if (!VP8GetBit(br, p[6])) {
 400       if (!VP8GetBit(br, p[7])) {
 401         v = 5 + VP8GetBit(br, 159);
 402       } else {
 403         v = 7 + 2 * VP8GetBit(br, 165);
 404         v += VP8GetBit(br, 145);
 405       }
 406     } else {
 407       const uint8_t* tab;
 408       const int bit1 = VP8GetBit(br, p[8]);
 409       const int bit0 = VP8GetBit(br, p[9 + bit1]);
 410       const int cat = 2 * bit1 + bit0;
 411       v = 0;
 412       for (tab = kCat3456[cat]; *tab; ++tab) {
 413         v += v + VP8GetBit(br, *tab);
 414       }
 415       v += 3 + (8 << cat);
 416     }
 417   }
 418   return v;
 419 }
 420
 421 // Returns the position of the last non-zero coeff plus one
 422 static int GetCoeffs(VP8BitReader* const br, const VP8BandProbas* const prob,
 423                      int ctx, const quant_t dq, int n, int16_t* out) {
 424   // n is either 0 or 1 here. kBands[n] is not necessary for extracting '*p'.
 425   const uint8_t* p = prob[n].probas_[ctx];
 426   for (; n < 16; ++n) {
 427     if (!VP8GetBit(br, p[0])) {
 428       return n;  // previous coeff was last non-zero coeff
 429     }
 430     while (!VP8GetBit(br, p[1])) {       // sequence of zero coeffs
 431       p = prob[kBands[++n]].probas_[0];
 432       if (n == 16) return 16;
 433     }
 434     {        // non zero coeff
 435       const VP8ProbaArray* const p_ctx = &prob[kBands[n + 1]].probas_[0];
 436       int v;
 437       if (!VP8GetBit(br, p[2])) {
 438         v = 1;
 439         p = p_ctx[1];
 440       } else {
 441         v = GetLargeValue(br, p);
 442         p = p_ctx[2];
 443       }
 444       out[kZigzag[n]] = VP8GetSigned(br, v) * dq[n > 0];
 445     }
 446   }
 447   return 16;
 448 }
 449
 450 static WEBP_INLINE uint32_t NzCodeBits(uint32_t nz_coeffs, int nz, int dc_nz) {
 451   nz_coeffs <<= 2;
 452   nz_coeffs |= (nz > 3) ? 3 : (nz > 1) ? 2 : dc_nz;
 453   return nz_coeffs;
 454 }
 455
 456 static int ParseResiduals(VP8Decoder* const dec,
 457                           VP8MB* const mb, VP8BitReader* const token_br) {
 458   VP8BandProbas (* const bands)[NUM_BANDS] = dec->proba_.bands_;
 459   const VP8BandProbas* ac_proba;
 460   VP8MBData* const block = dec->mb_data_ + dec->mb_x_;
 461   const VP8QuantMatrix* const q = &dec->dqm_[block->segment_];
 462   int16_t* dst = block->coeffs_;
 463   VP8MB* const left_mb = dec->mb_info_ - 1;
 464   uint8_t tnz, lnz;
 465   uint32_t non_zero_y = 0;
 466   uint32_t non_zero_uv = 0;
 467   int x, y, ch;
 468   uint32_t out_t_nz, out_l_nz;
 469   int first;
 470
 471   memset(dst, 0, 384 * sizeof(*dst));
 472   if (!block->is_i4x4_) {    // parse DC
 473     int16_t dc[16] = { 0 };
 474     const int ctx = mb->nz_dc_ + left_mb->nz_dc_;
 475     const int nz = GetCoeffs(token_br, bands[1], ctx, q->y2_mat_, 0, dc);
 476     mb->nz_dc_ = left_mb->nz_dc_ = (nz > 0);
 477     if (nz > 1) {   // more than just the DC -> perform the full transform
 478       VP8TransformWHT(dc, dst);
 479     } else {        // only DC is non-zero -> inlined simplified transform
 480       int i;
 481       const int dc0 = (dc[0] + 3) >> 3;
 482       for (i = 0; i < 16 * 16; i += 16) dst[i] = dc0;
 483     }
 484     first = 1;
 485     ac_proba = bands[0];
 486   } else {
 487     first = 0;
 488     ac_proba = bands[3];
 489   }
 490
 491   tnz = mb->nz_ & 0x0f;
 492   lnz = left_mb->nz_ & 0x0f;
 493   for (y = 0; y < 4; ++y) {
 494     int l = lnz & 1;
 495     uint32_t nz_coeffs = 0;
 496     for (x = 0; x < 4; ++x) {
 497       const int ctx = l + (tnz & 1);
 498       const int nz = GetCoeffs(token_br, ac_proba, ctx, q->y1_mat_, first, dst);
 499       l = (nz > first);
 500       tnz = (tnz >> 1) | (l << 7);
 501       nz_coeffs = NzCodeBits(nz_coeffs, nz, dst[0] != 0);
 502       dst += 16;
 503     }
 504     tnz >>= 4;
 505     lnz = (lnz >> 1) | (l << 7);
 506     non_zero_y = (non_zero_y << 8) | nz_coeffs;
 507   }
 508   out_t_nz = tnz;
 509   out_l_nz = lnz >> 4;
 510
 511   for (ch = 0; ch < 4; ch += 2) {
 512     uint32_t nz_coeffs = 0;
 513     tnz = mb->nz_ >> (4 + ch);
 514     lnz = left_mb->nz_ >> (4 + ch);
 515     for (y = 0; y < 2; ++y) {
 516       int l = lnz & 1;
 517       for (x = 0; x < 2; ++x) {
 518         const int ctx = l + (tnz & 1);
 519         const int nz = GetCoeffs(token_br, bands[2], ctx, q->uv_mat_, 0, dst);
 520         l = (nz > 0);
 521         tnz = (tnz >> 1) | (l << 3);
 522         nz_coeffs = NzCodeBits(nz_coeffs, nz, dst[0] != 0);
 523         dst += 16;
 524       }
 525       tnz >>= 2;
 526       lnz = (lnz >> 1) | (l << 5);
 527     }
 528     // Note: we don't really need the per-4x4 details for U/V blocks.
 529     non_zero_uv |= nz_coeffs << (4 * ch);
 530     out_t_nz |= (tnz << 4) << ch;
 531     out_l_nz |= (lnz & 0xf0) << ch;
 532   }
 533   mb->nz_ = out_t_nz;
 534   left_mb->nz_ = out_l_nz;
 535
 536   block->non_zero_y_ = non_zero_y;
 537   block->non_zero_uv_ = non_zero_uv;
 538
 539   // We look at the mode-code of each block and check if some blocks have less
 540   // than three non-zero coeffs (code < 2). This is to avoid dithering flat and
 541   // empty blocks.
 542   block->dither_ = (non_zero_uv & 0xaaaa) ? 0 : q->dither_;
 543
 544   return !(non_zero_y | non_zero_uv);  // will be used for further optimization
 545 }
 546
 547 //------------------------------------------------------------------------------
 548 // Main loop
 549
 550 int VP8DecodeMB(VP8Decoder* const dec, VP8BitReader* const token_br) {
 551   VP8MB* const left = dec->mb_info_ - 1;
 552   VP8MB* const mb = dec->mb_info_ + dec->mb_x_;
 553   VP8MBData* const block = dec->mb_data_ + dec->mb_x_;
 554   int skip = dec->use_skip_proba_ ? block->skip_ : 0;
 555
 556   if (!skip) {
 557     skip = ParseResiduals(dec, mb, token_br);
 558   } else {
 559     left->nz_ = mb->nz_ = 0;
 560     if (!block->is_i4x4_) {
 561       left->nz_dc_ = mb->nz_dc_ = 0;
 562     }
 563     block->non_zero_y_ = 0;
 564     block->non_zero_uv_ = 0;
 565     block->dither_ = 0;
 566   }
 567
 568   if (dec->filter_type_ > 0) {  // store filter info
 569     VP8FInfo* const finfo = dec->f_info_ + dec->mb_x_;
 570     *finfo = dec->fstrengths_[block->segment_][block->is_i4x4_];
 571     finfo->f_inner_ |= !skip;
 572   }
 573
 574   return !token_br->eof_;
 575 }
 576
 577 void VP8InitScanline(VP8Decoder* const dec) {
 578   VP8MB* const left = dec->mb_info_ - 1;
 579   left->nz_ = 0;
 580   left->nz_dc_ = 0;
 581   memset(dec->intra_l_, B_DC_PRED, sizeof(dec->intra_l_));
 582   dec->mb_x_ = 0;
 583 }
 584
 585 static int ParseFrame(VP8Decoder* const dec, VP8Io* io) {
 586   for (dec->mb_y_ = 0; dec->mb_y_ < dec->br_mb_y_; ++dec->mb_y_) {
 587     // Parse bitstream for this row.
 588     VP8BitReader* const token_br =
 589         &dec->parts_[dec->mb_y_ & (dec->num_parts_ - 1)];
 590     if (!VP8ParseIntraModeRow(&dec->br_, dec)) {
 591       return VP8SetError(dec, VP8_STATUS_NOT_ENOUGH_DATA,
 592                          "Premature end-of-partition0 encountered.");
 593     }
 594     for (; dec->mb_x_ < dec->mb_w_; ++dec->mb_x_) {
 595       if (!VP8DecodeMB(dec, token_br)) {
 596         return VP8SetError(dec, VP8_STATUS_NOT_ENOUGH_DATA,
 597                            "Premature end-of-file encountered.");
 598       }
 599     }
 600     VP8InitScanline(dec);   // Prepare for next scanline
 601
 602     // Reconstruct, filter and emit the row.
 603     if (!VP8ProcessRow(dec, io)) {
 604       return VP8SetError(dec, VP8_STATUS_USER_ABORT, "Output aborted.");
 605     }
 606   }
 607   if (dec->mt_method_ > 0) {
 608     if (!WebPGetWorkerInterface()->Sync(&dec->worker_)) return 0;
 609   }
 610
 611   return 1;
 612 }
 613
 614 // Main entry point
 615 int VP8Decode(VP8Decoder* const dec, VP8Io* const io) {
 616   int ok = 0;
 617   if (dec == NULL) {
 618     return 0;
 619   }
 620   if (io == NULL) {
 621     return VP8SetError(dec, VP8_STATUS_INVALID_PARAM,
 622                        "NULL VP8Io parameter in VP8Decode().");
 623   }
 624
 625   if (!dec->ready_) {
 626     if (!VP8GetHeaders(dec, io)) {
 627       return 0;
 628     }
 629   }
 630   assert(dec->ready_);
 631
 632   // Finish setting up the decoding parameter. Will call io->setup().
 633   ok = (VP8EnterCritical(dec, io) == VP8_STATUS_OK);
 634   if (ok) {   // good to go.
 635     // Will allocate memory and prepare everything.
 636     if (ok) ok = VP8InitFrame(dec, io);
 637
 638     // Main decoding loop
 639     if (ok) ok = ParseFrame(dec, io);
 640
 641     // Exit.
 642     ok &= VP8ExitCritical(dec, io);
 643   }
 644
 645   if (!ok) {
 646     VP8Clear(dec);
 647     return 0;
 648   }
 649
 650   dec->ready_ = 0;
 651   return ok;
 652 }
 653
 654 void VP8Clear(VP8Decoder* const dec) {
 655   if (dec == NULL) {
 656     return;
 657   }
 658   WebPGetWorkerInterface()->End(&dec->worker_);
 659   ALPHDelete(dec->alph_dec_);
 660   dec->alph_dec_ = NULL;
 661   WebPSafeFree(dec->mem_);
 662   dec->mem_ = NULL;
 663   dec->mem_size_ = 0;
 664   memset(&dec->br_, 0, sizeof(dec->br_));
 665   dec->ready_ = 0;
 666 }
 667
 668 //------------------------------------------------------------------------------
 669