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      1 // Copyright 2011 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 // Set and delete APIs for mux.
     11 //
     12 // Authors: Urvang (urvang (at) google.com)
     13 //          Vikas (vikasa (at) google.com)
     14 
     15 #include <assert.h>
     16 #include "src/mux/muxi.h"
     17 #include "src/utils/utils.h"
     18 
     19 //------------------------------------------------------------------------------
     20 // Life of a mux object.
     21 
     22 static void MuxInit(WebPMux* const mux) {
     23   assert(mux != NULL);
     24   memset(mux, 0, sizeof(*mux));
     25   mux->canvas_width_ = 0;     // just to be explicit
     26   mux->canvas_height_ = 0;
     27 }
     28 
     29 WebPMux* WebPNewInternal(int version) {
     30   if (WEBP_ABI_IS_INCOMPATIBLE(version, WEBP_MUX_ABI_VERSION)) {
     31     return NULL;
     32   } else {
     33     WebPMux* const mux = (WebPMux*)WebPSafeMalloc(1ULL, sizeof(WebPMux));
     34     if (mux != NULL) MuxInit(mux);
     35     return mux;
     36   }
     37 }
     38 
     39 // Delete all images in 'wpi_list'.
     40 static void DeleteAllImages(WebPMuxImage** const wpi_list) {
     41   while (*wpi_list != NULL) {
     42     *wpi_list = MuxImageDelete(*wpi_list);
     43   }
     44 }
     45 
     46 static void MuxRelease(WebPMux* const mux) {
     47   assert(mux != NULL);
     48   DeleteAllImages(&mux->images_);
     49   ChunkListDelete(&mux->vp8x_);
     50   ChunkListDelete(&mux->iccp_);
     51   ChunkListDelete(&mux->anim_);
     52   ChunkListDelete(&mux->exif_);
     53   ChunkListDelete(&mux->xmp_);
     54   ChunkListDelete(&mux->unknown_);
     55 }
     56 
     57 void WebPMuxDelete(WebPMux* mux) {
     58   if (mux != NULL) {
     59     MuxRelease(mux);
     60     WebPSafeFree(mux);
     61   }
     62 }
     63 
     64 //------------------------------------------------------------------------------
     65 // Helper method(s).
     66 
     67 // Handy MACRO, makes MuxSet() very symmetric to MuxGet().
     68 #define SWITCH_ID_LIST(INDEX, LIST)                                            \
     69   if (idx == (INDEX)) {                                                        \
     70     err = ChunkAssignData(&chunk, data, copy_data, tag);                       \
     71     if (err == WEBP_MUX_OK) {                                                  \
     72       err = ChunkSetNth(&chunk, (LIST), nth);                                  \
     73     }                                                                          \
     74     return err;                                                                \
     75   }
     76 
     77 static WebPMuxError MuxSet(WebPMux* const mux, uint32_t tag, uint32_t nth,
     78                            const WebPData* const data, int copy_data) {
     79   WebPChunk chunk;
     80   WebPMuxError err = WEBP_MUX_NOT_FOUND;
     81   const CHUNK_INDEX idx = ChunkGetIndexFromTag(tag);
     82   assert(mux != NULL);
     83   assert(!IsWPI(kChunks[idx].id));
     84 
     85   ChunkInit(&chunk);
     86   SWITCH_ID_LIST(IDX_VP8X,    &mux->vp8x_);
     87   SWITCH_ID_LIST(IDX_ICCP,    &mux->iccp_);
     88   SWITCH_ID_LIST(IDX_ANIM,    &mux->anim_);
     89   SWITCH_ID_LIST(IDX_EXIF,    &mux->exif_);
     90   SWITCH_ID_LIST(IDX_XMP,     &mux->xmp_);
     91   SWITCH_ID_LIST(IDX_UNKNOWN, &mux->unknown_);
     92   return err;
     93 }
     94 #undef SWITCH_ID_LIST
     95 
     96 // Create data for frame given image data, offsets and duration.
     97 static WebPMuxError CreateFrameData(
     98     int width, int height, const WebPMuxFrameInfo* const info,
     99     WebPData* const frame) {
    100   uint8_t* frame_bytes;
    101   const size_t frame_size = kChunks[IDX_ANMF].size;
    102 
    103   assert(width > 0 && height > 0 && info->duration >= 0);
    104   assert(info->dispose_method == (info->dispose_method & 1));
    105   // Note: assertion on upper bounds is done in PutLE24().
    106 
    107   frame_bytes = (uint8_t*)WebPSafeMalloc(1ULL, frame_size);
    108   if (frame_bytes == NULL) return WEBP_MUX_MEMORY_ERROR;
    109 
    110   PutLE24(frame_bytes + 0, info->x_offset / 2);
    111   PutLE24(frame_bytes + 3, info->y_offset / 2);
    112 
    113   PutLE24(frame_bytes + 6, width - 1);
    114   PutLE24(frame_bytes + 9, height - 1);
    115   PutLE24(frame_bytes + 12, info->duration);
    116   frame_bytes[15] =
    117       (info->blend_method == WEBP_MUX_NO_BLEND ? 2 : 0) |
    118       (info->dispose_method == WEBP_MUX_DISPOSE_BACKGROUND ? 1 : 0);
    119 
    120   frame->bytes = frame_bytes;
    121   frame->size = frame_size;
    122   return WEBP_MUX_OK;
    123 }
    124 
    125 // Outputs image data given a bitstream. The bitstream can either be a
    126 // single-image WebP file or raw VP8/VP8L data.
    127 // Also outputs 'is_lossless' to be true if the given bitstream is lossless.
    128 static WebPMuxError GetImageData(const WebPData* const bitstream,
    129                                  WebPData* const image, WebPData* const alpha,
    130                                  int* const is_lossless) {
    131   WebPDataInit(alpha);  // Default: no alpha.
    132   if (bitstream->size < TAG_SIZE ||
    133       memcmp(bitstream->bytes, "RIFF", TAG_SIZE)) {
    134     // It is NOT webp file data. Return input data as is.
    135     *image = *bitstream;
    136   } else {
    137     // It is webp file data. Extract image data from it.
    138     const WebPMuxImage* wpi;
    139     WebPMux* const mux = WebPMuxCreate(bitstream, 0);
    140     if (mux == NULL) return WEBP_MUX_BAD_DATA;
    141     wpi = mux->images_;
    142     assert(wpi != NULL && wpi->img_ != NULL);
    143     *image = wpi->img_->data_;
    144     if (wpi->alpha_ != NULL) {
    145       *alpha = wpi->alpha_->data_;
    146     }
    147     WebPMuxDelete(mux);
    148   }
    149   *is_lossless = VP8LCheckSignature(image->bytes, image->size);
    150   return WEBP_MUX_OK;
    151 }
    152 
    153 static WebPMuxError DeleteChunks(WebPChunk** chunk_list, uint32_t tag) {
    154   WebPMuxError err = WEBP_MUX_NOT_FOUND;
    155   assert(chunk_list);
    156   while (*chunk_list) {
    157     WebPChunk* const chunk = *chunk_list;
    158     if (chunk->tag_ == tag) {
    159       *chunk_list = ChunkDelete(chunk);
    160       err = WEBP_MUX_OK;
    161     } else {
    162       chunk_list = &chunk->next_;
    163     }
    164   }
    165   return err;
    166 }
    167 
    168 static WebPMuxError MuxDeleteAllNamedData(WebPMux* const mux, uint32_t tag) {
    169   const WebPChunkId id = ChunkGetIdFromTag(tag);
    170   assert(mux != NULL);
    171   if (IsWPI(id)) return WEBP_MUX_INVALID_ARGUMENT;
    172   return DeleteChunks(MuxGetChunkListFromId(mux, id), tag);
    173 }
    174 
    175 //------------------------------------------------------------------------------
    176 // Set API(s).
    177 
    178 WebPMuxError WebPMuxSetChunk(WebPMux* mux, const char fourcc[4],
    179                              const WebPData* chunk_data, int copy_data) {
    180   uint32_t tag;
    181   WebPMuxError err;
    182   if (mux == NULL || fourcc == NULL || chunk_data == NULL ||
    183       chunk_data->bytes == NULL || chunk_data->size > MAX_CHUNK_PAYLOAD) {
    184     return WEBP_MUX_INVALID_ARGUMENT;
    185   }
    186   tag = ChunkGetTagFromFourCC(fourcc);
    187 
    188   // Delete existing chunk(s) with the same 'fourcc'.
    189   err = MuxDeleteAllNamedData(mux, tag);
    190   if (err != WEBP_MUX_OK && err != WEBP_MUX_NOT_FOUND) return err;
    191 
    192   // Add the given chunk.
    193   return MuxSet(mux, tag, 1, chunk_data, copy_data);
    194 }
    195 
    196 // Creates a chunk from given 'data' and sets it as 1st chunk in 'chunk_list'.
    197 static WebPMuxError AddDataToChunkList(
    198     const WebPData* const data, int copy_data, uint32_t tag,
    199     WebPChunk** chunk_list) {
    200   WebPChunk chunk;
    201   WebPMuxError err;
    202   ChunkInit(&chunk);
    203   err = ChunkAssignData(&chunk, data, copy_data, tag);
    204   if (err != WEBP_MUX_OK) goto Err;
    205   err = ChunkSetNth(&chunk, chunk_list, 1);
    206   if (err != WEBP_MUX_OK) goto Err;
    207   return WEBP_MUX_OK;
    208  Err:
    209   ChunkRelease(&chunk);
    210   return err;
    211 }
    212 
    213 // Extracts image & alpha data from the given bitstream and then sets wpi.alpha_
    214 // and wpi.img_ appropriately.
    215 static WebPMuxError SetAlphaAndImageChunks(
    216     const WebPData* const bitstream, int copy_data, WebPMuxImage* const wpi) {
    217   int is_lossless = 0;
    218   WebPData image, alpha;
    219   WebPMuxError err = GetImageData(bitstream, &image, &alpha, &is_lossless);
    220   const int image_tag =
    221       is_lossless ? kChunks[IDX_VP8L].tag : kChunks[IDX_VP8].tag;
    222   if (err != WEBP_MUX_OK) return err;
    223   if (alpha.bytes != NULL) {
    224     err = AddDataToChunkList(&alpha, copy_data, kChunks[IDX_ALPHA].tag,
    225                              &wpi->alpha_);
    226     if (err != WEBP_MUX_OK) return err;
    227   }
    228   err = AddDataToChunkList(&image, copy_data, image_tag, &wpi->img_);
    229   if (err != WEBP_MUX_OK) return err;
    230   return MuxImageFinalize(wpi) ? WEBP_MUX_OK : WEBP_MUX_INVALID_ARGUMENT;
    231 }
    232 
    233 WebPMuxError WebPMuxSetImage(WebPMux* mux, const WebPData* bitstream,
    234                              int copy_data) {
    235   WebPMuxImage wpi;
    236   WebPMuxError err;
    237 
    238   // Sanity checks.
    239   if (mux == NULL || bitstream == NULL || bitstream->bytes == NULL ||
    240       bitstream->size > MAX_CHUNK_PAYLOAD) {
    241     return WEBP_MUX_INVALID_ARGUMENT;
    242   }
    243 
    244   if (mux->images_ != NULL) {
    245     // Only one 'simple image' can be added in mux. So, remove present images.
    246     DeleteAllImages(&mux->images_);
    247   }
    248 
    249   MuxImageInit(&wpi);
    250   err = SetAlphaAndImageChunks(bitstream, copy_data, &wpi);
    251   if (err != WEBP_MUX_OK) goto Err;
    252 
    253   // Add this WebPMuxImage to mux.
    254   err = MuxImagePush(&wpi, &mux->images_);
    255   if (err != WEBP_MUX_OK) goto Err;
    256 
    257   // All is well.
    258   return WEBP_MUX_OK;
    259 
    260  Err:  // Something bad happened.
    261   MuxImageRelease(&wpi);
    262   return err;
    263 }
    264 
    265 WebPMuxError WebPMuxPushFrame(WebPMux* mux, const WebPMuxFrameInfo* info,
    266                               int copy_data) {
    267   WebPMuxImage wpi;
    268   WebPMuxError err;
    269   const WebPData* const bitstream = &info->bitstream;
    270 
    271   // Sanity checks.
    272   if (mux == NULL || info == NULL) return WEBP_MUX_INVALID_ARGUMENT;
    273 
    274   if (info->id != WEBP_CHUNK_ANMF) return WEBP_MUX_INVALID_ARGUMENT;
    275 
    276   if (bitstream->bytes == NULL || bitstream->size > MAX_CHUNK_PAYLOAD) {
    277     return WEBP_MUX_INVALID_ARGUMENT;
    278   }
    279 
    280   if (mux->images_ != NULL) {
    281     const WebPMuxImage* const image = mux->images_;
    282     const uint32_t image_id = (image->header_ != NULL) ?
    283         ChunkGetIdFromTag(image->header_->tag_) : WEBP_CHUNK_IMAGE;
    284     if (image_id != info->id) {
    285       return WEBP_MUX_INVALID_ARGUMENT;  // Conflicting frame types.
    286     }
    287   }
    288 
    289   MuxImageInit(&wpi);
    290   err = SetAlphaAndImageChunks(bitstream, copy_data, &wpi);
    291   if (err != WEBP_MUX_OK) goto Err;
    292   assert(wpi.img_ != NULL);  // As SetAlphaAndImageChunks() was successful.
    293 
    294   {
    295     WebPData frame;
    296     const uint32_t tag = kChunks[IDX_ANMF].tag;
    297     WebPMuxFrameInfo tmp = *info;
    298     tmp.x_offset &= ~1;  // Snap offsets to even.
    299     tmp.y_offset &= ~1;
    300     if (tmp.x_offset < 0 || tmp.x_offset >= MAX_POSITION_OFFSET ||
    301         tmp.y_offset < 0 || tmp.y_offset >= MAX_POSITION_OFFSET ||
    302         (tmp.duration < 0 || tmp.duration >= MAX_DURATION) ||
    303         tmp.dispose_method != (tmp.dispose_method & 1)) {
    304       err = WEBP_MUX_INVALID_ARGUMENT;
    305       goto Err;
    306     }
    307     err = CreateFrameData(wpi.width_, wpi.height_, &tmp, &frame);
    308     if (err != WEBP_MUX_OK) goto Err;
    309     // Add frame chunk (with copy_data = 1).
    310     err = AddDataToChunkList(&frame, 1, tag, &wpi.header_);
    311     WebPDataClear(&frame);  // frame owned by wpi.header_ now.
    312     if (err != WEBP_MUX_OK) goto Err;
    313   }
    314 
    315   // Add this WebPMuxImage to mux.
    316   err = MuxImagePush(&wpi, &mux->images_);
    317   if (err != WEBP_MUX_OK) goto Err;
    318 
    319   // All is well.
    320   return WEBP_MUX_OK;
    321 
    322  Err:  // Something bad happened.
    323   MuxImageRelease(&wpi);
    324   return err;
    325 }
    326 
    327 WebPMuxError WebPMuxSetAnimationParams(WebPMux* mux,
    328                                        const WebPMuxAnimParams* params) {
    329   WebPMuxError err;
    330   uint8_t data[ANIM_CHUNK_SIZE];
    331   const WebPData anim = { data, ANIM_CHUNK_SIZE };
    332 
    333   if (mux == NULL || params == NULL) return WEBP_MUX_INVALID_ARGUMENT;
    334   if (params->loop_count < 0 || params->loop_count >= MAX_LOOP_COUNT) {
    335     return WEBP_MUX_INVALID_ARGUMENT;
    336   }
    337 
    338   // Delete any existing ANIM chunk(s).
    339   err = MuxDeleteAllNamedData(mux, kChunks[IDX_ANIM].tag);
    340   if (err != WEBP_MUX_OK && err != WEBP_MUX_NOT_FOUND) return err;
    341 
    342   // Set the animation parameters.
    343   PutLE32(data, params->bgcolor);
    344   PutLE16(data + 4, params->loop_count);
    345   return MuxSet(mux, kChunks[IDX_ANIM].tag, 1, &anim, 1);
    346 }
    347 
    348 WebPMuxError WebPMuxSetCanvasSize(WebPMux* mux,
    349                                   int width, int height) {
    350   WebPMuxError err;
    351   if (mux == NULL) {
    352     return WEBP_MUX_INVALID_ARGUMENT;
    353   }
    354   if (width < 0 || height < 0 ||
    355       width > MAX_CANVAS_SIZE || height > MAX_CANVAS_SIZE) {
    356     return WEBP_MUX_INVALID_ARGUMENT;
    357   }
    358   if (width * (uint64_t)height >= MAX_IMAGE_AREA) {
    359     return WEBP_MUX_INVALID_ARGUMENT;
    360   }
    361   if ((width * height) == 0 && (width | height) != 0) {
    362     // one of width / height is zero, but not both -> invalid!
    363     return WEBP_MUX_INVALID_ARGUMENT;
    364   }
    365   // If we already assembled a VP8X chunk, invalidate it.
    366   err = MuxDeleteAllNamedData(mux, kChunks[IDX_VP8X].tag);
    367   if (err != WEBP_MUX_OK && err != WEBP_MUX_NOT_FOUND) return err;
    368 
    369   mux->canvas_width_ = width;
    370   mux->canvas_height_ = height;
    371   return WEBP_MUX_OK;
    372 }
    373 
    374 //------------------------------------------------------------------------------
    375 // Delete API(s).
    376 
    377 WebPMuxError WebPMuxDeleteChunk(WebPMux* mux, const char fourcc[4]) {
    378   if (mux == NULL || fourcc == NULL) return WEBP_MUX_INVALID_ARGUMENT;
    379   return MuxDeleteAllNamedData(mux, ChunkGetTagFromFourCC(fourcc));
    380 }
    381 
    382 WebPMuxError WebPMuxDeleteFrame(WebPMux* mux, uint32_t nth) {
    383   if (mux == NULL) return WEBP_MUX_INVALID_ARGUMENT;
    384   return MuxImageDeleteNth(&mux->images_, nth);
    385 }
    386 
    387 //------------------------------------------------------------------------------
    388 // Assembly of the WebP RIFF file.
    389 
    390 static WebPMuxError GetFrameInfo(
    391     const WebPChunk* const frame_chunk,
    392     int* const x_offset, int* const y_offset, int* const duration) {
    393   const WebPData* const data = &frame_chunk->data_;
    394   const size_t expected_data_size = ANMF_CHUNK_SIZE;
    395   assert(frame_chunk->tag_ == kChunks[IDX_ANMF].tag);
    396   assert(frame_chunk != NULL);
    397   if (data->size != expected_data_size) return WEBP_MUX_INVALID_ARGUMENT;
    398 
    399   *x_offset = 2 * GetLE24(data->bytes + 0);
    400   *y_offset = 2 * GetLE24(data->bytes + 3);
    401   *duration = GetLE24(data->bytes + 12);
    402   return WEBP_MUX_OK;
    403 }
    404 
    405 static WebPMuxError GetImageInfo(const WebPMuxImage* const wpi,
    406                                  int* const x_offset, int* const y_offset,
    407                                  int* const duration,
    408                                  int* const width, int* const height) {
    409   const WebPChunk* const frame_chunk = wpi->header_;
    410   WebPMuxError err;
    411   assert(wpi != NULL);
    412   assert(frame_chunk != NULL);
    413 
    414   // Get offsets and duration from ANMF chunk.
    415   err = GetFrameInfo(frame_chunk, x_offset, y_offset, duration);
    416   if (err != WEBP_MUX_OK) return err;
    417 
    418   // Get width and height from VP8/VP8L chunk.
    419   if (width != NULL) *width = wpi->width_;
    420   if (height != NULL) *height = wpi->height_;
    421   return WEBP_MUX_OK;
    422 }
    423 
    424 // Returns the tightest dimension for the canvas considering the image list.
    425 static WebPMuxError GetAdjustedCanvasSize(const WebPMux* const mux,
    426                                           int* const width, int* const height) {
    427   WebPMuxImage* wpi = NULL;
    428   assert(mux != NULL);
    429   assert(width != NULL && height != NULL);
    430 
    431   wpi = mux->images_;
    432   assert(wpi != NULL);
    433   assert(wpi->img_ != NULL);
    434 
    435   if (wpi->next_ != NULL) {
    436     int max_x = 0, max_y = 0;
    437     // if we have a chain of wpi's, header_ is necessarily set
    438     assert(wpi->header_ != NULL);
    439     // Aggregate the bounding box for animation frames.
    440     for (; wpi != NULL; wpi = wpi->next_) {
    441       int x_offset = 0, y_offset = 0, duration = 0, w = 0, h = 0;
    442       const WebPMuxError err = GetImageInfo(wpi, &x_offset, &y_offset,
    443                                             &duration, &w, &h);
    444       const int max_x_pos = x_offset + w;
    445       const int max_y_pos = y_offset + h;
    446       if (err != WEBP_MUX_OK) return err;
    447       assert(x_offset < MAX_POSITION_OFFSET);
    448       assert(y_offset < MAX_POSITION_OFFSET);
    449 
    450       if (max_x_pos > max_x) max_x = max_x_pos;
    451       if (max_y_pos > max_y) max_y = max_y_pos;
    452     }
    453     *width = max_x;
    454     *height = max_y;
    455   } else {
    456     // For a single image, canvas dimensions are same as image dimensions.
    457     *width = wpi->width_;
    458     *height = wpi->height_;
    459   }
    460   return WEBP_MUX_OK;
    461 }
    462 
    463 // VP8X format:
    464 // Total Size : 10,
    465 // Flags  : 4 bytes,
    466 // Width  : 3 bytes,
    467 // Height : 3 bytes.
    468 static WebPMuxError CreateVP8XChunk(WebPMux* const mux) {
    469   WebPMuxError err = WEBP_MUX_OK;
    470   uint32_t flags = 0;
    471   int width = 0;
    472   int height = 0;
    473   uint8_t data[VP8X_CHUNK_SIZE];
    474   const WebPData vp8x = { data, VP8X_CHUNK_SIZE };
    475   const WebPMuxImage* images = NULL;
    476 
    477   assert(mux != NULL);
    478   images = mux->images_;  // First image.
    479   if (images == NULL || images->img_ == NULL ||
    480       images->img_->data_.bytes == NULL) {
    481     return WEBP_MUX_INVALID_ARGUMENT;
    482   }
    483 
    484   // If VP8X chunk(s) is(are) already present, remove them (and later add new
    485   // VP8X chunk with updated flags).
    486   err = MuxDeleteAllNamedData(mux, kChunks[IDX_VP8X].tag);
    487   if (err != WEBP_MUX_OK && err != WEBP_MUX_NOT_FOUND) return err;
    488 
    489   // Set flags.
    490   if (mux->iccp_ != NULL && mux->iccp_->data_.bytes != NULL) {
    491     flags |= ICCP_FLAG;
    492   }
    493   if (mux->exif_ != NULL && mux->exif_->data_.bytes != NULL) {
    494     flags |= EXIF_FLAG;
    495   }
    496   if (mux->xmp_ != NULL && mux->xmp_->data_.bytes != NULL) {
    497     flags |= XMP_FLAG;
    498   }
    499   if (images->header_ != NULL) {
    500     if (images->header_->tag_ == kChunks[IDX_ANMF].tag) {
    501       // This is an image with animation.
    502       flags |= ANIMATION_FLAG;
    503     }
    504   }
    505   if (MuxImageCount(images, WEBP_CHUNK_ALPHA) > 0) {
    506     flags |= ALPHA_FLAG;  // Some images have an alpha channel.
    507   }
    508 
    509   err = GetAdjustedCanvasSize(mux, &width, &height);
    510   if (err != WEBP_MUX_OK) return err;
    511 
    512   if (width <= 0 || height <= 0) {
    513     return WEBP_MUX_INVALID_ARGUMENT;
    514   }
    515   if (width > MAX_CANVAS_SIZE || height > MAX_CANVAS_SIZE) {
    516     return WEBP_MUX_INVALID_ARGUMENT;
    517   }
    518 
    519   if (mux->canvas_width_ != 0 || mux->canvas_height_ != 0) {
    520     if (width > mux->canvas_width_ || height > mux->canvas_height_) {
    521       return WEBP_MUX_INVALID_ARGUMENT;
    522     }
    523     width = mux->canvas_width_;
    524     height = mux->canvas_height_;
    525   }
    526 
    527   if (flags == 0 && mux->unknown_ == NULL) {
    528     // For simple file format, VP8X chunk should not be added.
    529     return WEBP_MUX_OK;
    530   }
    531 
    532   if (MuxHasAlpha(images)) {
    533     // This means some frames explicitly/implicitly contain alpha.
    534     // Note: This 'flags' update must NOT be done for a lossless image
    535     // without a VP8X chunk!
    536     flags |= ALPHA_FLAG;
    537   }
    538 
    539   PutLE32(data + 0, flags);   // VP8X chunk flags.
    540   PutLE24(data + 4, width - 1);   // canvas width.
    541   PutLE24(data + 7, height - 1);  // canvas height.
    542 
    543   return MuxSet(mux, kChunks[IDX_VP8X].tag, 1, &vp8x, 1);
    544 }
    545 
    546 // Cleans up 'mux' by removing any unnecessary chunks.
    547 static WebPMuxError MuxCleanup(WebPMux* const mux) {
    548   int num_frames;
    549   int num_anim_chunks;
    550 
    551   // If we have an image with a single frame, and its rectangle
    552   // covers the whole canvas, convert it to a non-animated image
    553   // (to avoid writing ANMF chunk unnecessarily).
    554   WebPMuxError err = WebPMuxNumChunks(mux, kChunks[IDX_ANMF].id, &num_frames);
    555   if (err != WEBP_MUX_OK) return err;
    556   if (num_frames == 1) {
    557     WebPMuxImage* frame = NULL;
    558     err = MuxImageGetNth((const WebPMuxImage**)&mux->images_, 1, &frame);
    559     assert(err == WEBP_MUX_OK);  // We know that one frame does exist.
    560     assert(frame != NULL);
    561     if (frame->header_ != NULL &&
    562         ((mux->canvas_width_ == 0 && mux->canvas_height_ == 0) ||
    563          (frame->width_ == mux->canvas_width_ &&
    564           frame->height_ == mux->canvas_height_))) {
    565       assert(frame->header_->tag_ == kChunks[IDX_ANMF].tag);
    566       ChunkDelete(frame->header_);  // Removes ANMF chunk.
    567       frame->header_ = NULL;
    568       num_frames = 0;
    569     }
    570   }
    571   // Remove ANIM chunk if this is a non-animated image.
    572   err = WebPMuxNumChunks(mux, kChunks[IDX_ANIM].id, &num_anim_chunks);
    573   if (err != WEBP_MUX_OK) return err;
    574   if (num_anim_chunks >= 1 && num_frames == 0) {
    575     err = MuxDeleteAllNamedData(mux, kChunks[IDX_ANIM].tag);
    576     if (err != WEBP_MUX_OK) return err;
    577   }
    578   return WEBP_MUX_OK;
    579 }
    580 
    581 // Total size of a list of images.
    582 static size_t ImageListDiskSize(const WebPMuxImage* wpi_list) {
    583   size_t size = 0;
    584   while (wpi_list != NULL) {
    585     size += MuxImageDiskSize(wpi_list);
    586     wpi_list = wpi_list->next_;
    587   }
    588   return size;
    589 }
    590 
    591 // Write out the given list of images into 'dst'.
    592 static uint8_t* ImageListEmit(const WebPMuxImage* wpi_list, uint8_t* dst) {
    593   while (wpi_list != NULL) {
    594     dst = MuxImageEmit(wpi_list, dst);
    595     wpi_list = wpi_list->next_;
    596   }
    597   return dst;
    598 }
    599 
    600 WebPMuxError WebPMuxAssemble(WebPMux* mux, WebPData* assembled_data) {
    601   size_t size = 0;
    602   uint8_t* data = NULL;
    603   uint8_t* dst = NULL;
    604   WebPMuxError err;
    605 
    606   if (assembled_data == NULL) {
    607     return WEBP_MUX_INVALID_ARGUMENT;
    608   }
    609   // Clean up returned data, in case something goes wrong.
    610   memset(assembled_data, 0, sizeof(*assembled_data));
    611 
    612   if (mux == NULL) {
    613     return WEBP_MUX_INVALID_ARGUMENT;
    614   }
    615 
    616   // Finalize mux.
    617   err = MuxCleanup(mux);
    618   if (err != WEBP_MUX_OK) return err;
    619   err = CreateVP8XChunk(mux);
    620   if (err != WEBP_MUX_OK) return err;
    621 
    622   // Allocate data.
    623   size = ChunkListDiskSize(mux->vp8x_) + ChunkListDiskSize(mux->iccp_)
    624        + ChunkListDiskSize(mux->anim_) + ImageListDiskSize(mux->images_)
    625        + ChunkListDiskSize(mux->exif_) + ChunkListDiskSize(mux->xmp_)
    626        + ChunkListDiskSize(mux->unknown_) + RIFF_HEADER_SIZE;
    627 
    628   data = (uint8_t*)WebPSafeMalloc(1ULL, size);
    629   if (data == NULL) return WEBP_MUX_MEMORY_ERROR;
    630 
    631   // Emit header & chunks.
    632   dst = MuxEmitRiffHeader(data, size);
    633   dst = ChunkListEmit(mux->vp8x_, dst);
    634   dst = ChunkListEmit(mux->iccp_, dst);
    635   dst = ChunkListEmit(mux->anim_, dst);
    636   dst = ImageListEmit(mux->images_, dst);
    637   dst = ChunkListEmit(mux->exif_, dst);
    638   dst = ChunkListEmit(mux->xmp_, dst);
    639   dst = ChunkListEmit(mux->unknown_, dst);
    640   assert(dst == data + size);
    641 
    642   // Validate mux.
    643   err = MuxValidate(mux);
    644   if (err != WEBP_MUX_OK) {
    645     WebPSafeFree(data);
    646     data = NULL;
    647     size = 0;
    648   }
    649 
    650   // Finalize data.
    651   assembled_data->bytes = data;
    652   assembled_data->size = size;
    653 
    654   return err;
    655 }
    656 
    657 //------------------------------------------------------------------------------
    658