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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 // Internal objects and utils for mux.
11 //
12 // Authors: Urvang (urvang@google.com)
13 //          Vikas (vikasa@google.com)
14 
15 #include <assert.h>
16 #include "src/mux/muxi.h"
17 #include "src/utils/utils.h"
18 
19 #define UNDEFINED_CHUNK_SIZE ((uint32_t)(-1))
20 
21 const ChunkInfo kChunks[] = {
22   { MKFOURCC('V', 'P', '8', 'X'),  WEBP_CHUNK_VP8X,    VP8X_CHUNK_SIZE },
23   { MKFOURCC('I', 'C', 'C', 'P'),  WEBP_CHUNK_ICCP,    UNDEFINED_CHUNK_SIZE },
24   { MKFOURCC('A', 'N', 'I', 'M'),  WEBP_CHUNK_ANIM,    ANIM_CHUNK_SIZE },
25   { MKFOURCC('A', 'N', 'M', 'F'),  WEBP_CHUNK_ANMF,    ANMF_CHUNK_SIZE },
26   { MKFOURCC('A', 'L', 'P', 'H'),  WEBP_CHUNK_ALPHA,   UNDEFINED_CHUNK_SIZE },
27   { MKFOURCC('V', 'P', '8', ' '),  WEBP_CHUNK_IMAGE,   UNDEFINED_CHUNK_SIZE },
28   { MKFOURCC('V', 'P', '8', 'L'),  WEBP_CHUNK_IMAGE,   UNDEFINED_CHUNK_SIZE },
29   { MKFOURCC('E', 'X', 'I', 'F'),  WEBP_CHUNK_EXIF,    UNDEFINED_CHUNK_SIZE },
30   { MKFOURCC('X', 'M', 'P', ' '),  WEBP_CHUNK_XMP,     UNDEFINED_CHUNK_SIZE },
31   { NIL_TAG,                       WEBP_CHUNK_UNKNOWN, UNDEFINED_CHUNK_SIZE },
32 
33   { NIL_TAG,                       WEBP_CHUNK_NIL,     UNDEFINED_CHUNK_SIZE }
34 };
35 
36 //------------------------------------------------------------------------------
37 
WebPGetMuxVersion(void)38 int WebPGetMuxVersion(void) {
39   return (MUX_MAJ_VERSION << 16) | (MUX_MIN_VERSION << 8) | MUX_REV_VERSION;
40 }
41 
42 //------------------------------------------------------------------------------
43 // Life of a chunk object.
44 
ChunkInit(WebPChunk * const chunk)45 void ChunkInit(WebPChunk* const chunk) {
46   assert(chunk);
47   memset(chunk, 0, sizeof(*chunk));
48   chunk->tag_ = NIL_TAG;
49 }
50 
ChunkRelease(WebPChunk * const chunk)51 WebPChunk* ChunkRelease(WebPChunk* const chunk) {
52   WebPChunk* next;
53   if (chunk == NULL) return NULL;
54   if (chunk->owner_) {
55     WebPDataClear(&chunk->data_);
56   }
57   next = chunk->next_;
58   ChunkInit(chunk);
59   return next;
60 }
61 
62 //------------------------------------------------------------------------------
63 // Chunk misc methods.
64 
ChunkGetIndexFromTag(uint32_t tag)65 CHUNK_INDEX ChunkGetIndexFromTag(uint32_t tag) {
66   int i;
67   for (i = 0; kChunks[i].tag != NIL_TAG; ++i) {
68     if (tag == kChunks[i].tag) return (CHUNK_INDEX)i;
69   }
70   return IDX_UNKNOWN;
71 }
72 
ChunkGetIdFromTag(uint32_t tag)73 WebPChunkId ChunkGetIdFromTag(uint32_t tag) {
74   int i;
75   for (i = 0; kChunks[i].tag != NIL_TAG; ++i) {
76     if (tag == kChunks[i].tag) return kChunks[i].id;
77   }
78   return WEBP_CHUNK_UNKNOWN;
79 }
80 
ChunkGetTagFromFourCC(const char fourcc[4])81 uint32_t ChunkGetTagFromFourCC(const char fourcc[4]) {
82   return MKFOURCC(fourcc[0], fourcc[1], fourcc[2], fourcc[3]);
83 }
84 
ChunkGetIndexFromFourCC(const char fourcc[4])85 CHUNK_INDEX ChunkGetIndexFromFourCC(const char fourcc[4]) {
86   const uint32_t tag = ChunkGetTagFromFourCC(fourcc);
87   return ChunkGetIndexFromTag(tag);
88 }
89 
90 //------------------------------------------------------------------------------
91 // Chunk search methods.
92 
93 // Returns next chunk in the chunk list with the given tag.
ChunkSearchNextInList(WebPChunk * chunk,uint32_t tag)94 static WebPChunk* ChunkSearchNextInList(WebPChunk* chunk, uint32_t tag) {
95   while (chunk != NULL && chunk->tag_ != tag) {
96     chunk = chunk->next_;
97   }
98   return chunk;
99 }
100 
ChunkSearchList(WebPChunk * first,uint32_t nth,uint32_t tag)101 WebPChunk* ChunkSearchList(WebPChunk* first, uint32_t nth, uint32_t tag) {
102   uint32_t iter = nth;
103   first = ChunkSearchNextInList(first, tag);
104   if (first == NULL) return NULL;
105 
106   while (--iter != 0) {
107     WebPChunk* next_chunk = ChunkSearchNextInList(first->next_, tag);
108     if (next_chunk == NULL) break;
109     first = next_chunk;
110   }
111   return ((nth > 0) && (iter > 0)) ? NULL : first;
112 }
113 
114 // Outputs a pointer to 'prev_chunk->next_',
115 //   where 'prev_chunk' is the pointer to the chunk at position (nth - 1).
116 // Returns true if nth chunk was found.
ChunkSearchListToSet(WebPChunk ** chunk_list,uint32_t nth,WebPChunk *** const location)117 static int ChunkSearchListToSet(WebPChunk** chunk_list, uint32_t nth,
118                                 WebPChunk*** const location) {
119   uint32_t count = 0;
120   assert(chunk_list != NULL);
121   *location = chunk_list;
122 
123   while (*chunk_list != NULL) {
124     WebPChunk* const cur_chunk = *chunk_list;
125     ++count;
126     if (count == nth) return 1;  // Found.
127     chunk_list = &cur_chunk->next_;
128     *location = chunk_list;
129   }
130 
131   // *chunk_list is ok to be NULL if adding at last location.
132   return (nth == 0 || (count == nth - 1)) ? 1 : 0;
133 }
134 
135 //------------------------------------------------------------------------------
136 // Chunk writer methods.
137 
ChunkAssignData(WebPChunk * chunk,const WebPData * const data,int copy_data,uint32_t tag)138 WebPMuxError ChunkAssignData(WebPChunk* chunk, const WebPData* const data,
139                              int copy_data, uint32_t tag) {
140   // For internally allocated chunks, always copy data & make it owner of data.
141   if (tag == kChunks[IDX_VP8X].tag || tag == kChunks[IDX_ANIM].tag) {
142     copy_data = 1;
143   }
144 
145   ChunkRelease(chunk);
146 
147   if (data != NULL) {
148     if (copy_data) {        // Copy data.
149       if (!WebPDataCopy(data, &chunk->data_)) return WEBP_MUX_MEMORY_ERROR;
150       chunk->owner_ = 1;    // Chunk is owner of data.
151     } else {                // Don't copy data.
152       chunk->data_ = *data;
153     }
154   }
155   chunk->tag_ = tag;
156   return WEBP_MUX_OK;
157 }
158 
ChunkSetNth(WebPChunk * chunk,WebPChunk ** chunk_list,uint32_t nth)159 WebPMuxError ChunkSetNth(WebPChunk* chunk, WebPChunk** chunk_list,
160                          uint32_t nth) {
161   WebPChunk* new_chunk;
162 
163   if (!ChunkSearchListToSet(chunk_list, nth, &chunk_list)) {
164     return WEBP_MUX_NOT_FOUND;
165   }
166 
167   new_chunk = (WebPChunk*)WebPSafeMalloc(1ULL, sizeof(*new_chunk));
168   if (new_chunk == NULL) return WEBP_MUX_MEMORY_ERROR;
169   *new_chunk = *chunk;
170   chunk->owner_ = 0;
171   new_chunk->next_ = *chunk_list;
172   *chunk_list = new_chunk;
173   return WEBP_MUX_OK;
174 }
175 
176 //------------------------------------------------------------------------------
177 // Chunk deletion method(s).
178 
ChunkDelete(WebPChunk * const chunk)179 WebPChunk* ChunkDelete(WebPChunk* const chunk) {
180   WebPChunk* const next = ChunkRelease(chunk);
181   WebPSafeFree(chunk);
182   return next;
183 }
184 
ChunkListDelete(WebPChunk ** const chunk_list)185 void ChunkListDelete(WebPChunk** const chunk_list) {
186   while (*chunk_list != NULL) {
187     *chunk_list = ChunkDelete(*chunk_list);
188   }
189 }
190 
191 //------------------------------------------------------------------------------
192 // Chunk serialization methods.
193 
ChunkEmit(const WebPChunk * const chunk,uint8_t * dst)194 static uint8_t* ChunkEmit(const WebPChunk* const chunk, uint8_t* dst) {
195   const size_t chunk_size = chunk->data_.size;
196   assert(chunk);
197   assert(chunk->tag_ != NIL_TAG);
198   PutLE32(dst + 0, chunk->tag_);
199   PutLE32(dst + TAG_SIZE, (uint32_t)chunk_size);
200   assert(chunk_size == (uint32_t)chunk_size);
201   memcpy(dst + CHUNK_HEADER_SIZE, chunk->data_.bytes, chunk_size);
202   if (chunk_size & 1)
203     dst[CHUNK_HEADER_SIZE + chunk_size] = 0;  // Add padding.
204   return dst + ChunkDiskSize(chunk);
205 }
206 
ChunkListEmit(const WebPChunk * chunk_list,uint8_t * dst)207 uint8_t* ChunkListEmit(const WebPChunk* chunk_list, uint8_t* dst) {
208   while (chunk_list != NULL) {
209     dst = ChunkEmit(chunk_list, dst);
210     chunk_list = chunk_list->next_;
211   }
212   return dst;
213 }
214 
ChunkListDiskSize(const WebPChunk * chunk_list)215 size_t ChunkListDiskSize(const WebPChunk* chunk_list) {
216   size_t size = 0;
217   while (chunk_list != NULL) {
218     size += ChunkDiskSize(chunk_list);
219     chunk_list = chunk_list->next_;
220   }
221   return size;
222 }
223 
224 //------------------------------------------------------------------------------
225 // Life of a MuxImage object.
226 
MuxImageInit(WebPMuxImage * const wpi)227 void MuxImageInit(WebPMuxImage* const wpi) {
228   assert(wpi);
229   memset(wpi, 0, sizeof(*wpi));
230 }
231 
MuxImageRelease(WebPMuxImage * const wpi)232 WebPMuxImage* MuxImageRelease(WebPMuxImage* const wpi) {
233   WebPMuxImage* next;
234   if (wpi == NULL) return NULL;
235   ChunkDelete(wpi->header_);
236   ChunkDelete(wpi->alpha_);
237   ChunkDelete(wpi->img_);
238   ChunkListDelete(&wpi->unknown_);
239 
240   next = wpi->next_;
241   MuxImageInit(wpi);
242   return next;
243 }
244 
245 //------------------------------------------------------------------------------
246 // MuxImage search methods.
247 
248 // Get a reference to appropriate chunk list within an image given chunk tag.
GetChunkListFromId(const WebPMuxImage * const wpi,WebPChunkId id)249 static WebPChunk** GetChunkListFromId(const WebPMuxImage* const wpi,
250                                       WebPChunkId id) {
251   assert(wpi != NULL);
252   switch (id) {
253     case WEBP_CHUNK_ANMF:  return (WebPChunk**)&wpi->header_;
254     case WEBP_CHUNK_ALPHA: return (WebPChunk**)&wpi->alpha_;
255     case WEBP_CHUNK_IMAGE: return (WebPChunk**)&wpi->img_;
256     default: return NULL;
257   }
258 }
259 
MuxImageCount(const WebPMuxImage * wpi_list,WebPChunkId id)260 int MuxImageCount(const WebPMuxImage* wpi_list, WebPChunkId id) {
261   int count = 0;
262   const WebPMuxImage* current;
263   for (current = wpi_list; current != NULL; current = current->next_) {
264     if (id == WEBP_CHUNK_NIL) {
265       ++count;  // Special case: count all images.
266     } else {
267       const WebPChunk* const wpi_chunk = *GetChunkListFromId(current, id);
268       if (wpi_chunk != NULL) {
269         const WebPChunkId wpi_chunk_id = ChunkGetIdFromTag(wpi_chunk->tag_);
270         if (wpi_chunk_id == id) ++count;  // Count images with a matching 'id'.
271       }
272     }
273   }
274   return count;
275 }
276 
277 // Outputs a pointer to 'prev_wpi->next_',
278 //   where 'prev_wpi' is the pointer to the image at position (nth - 1).
279 // Returns true if nth image was found.
SearchImageToGetOrDelete(WebPMuxImage ** wpi_list,uint32_t nth,WebPMuxImage *** const location)280 static int SearchImageToGetOrDelete(WebPMuxImage** wpi_list, uint32_t nth,
281                                     WebPMuxImage*** const location) {
282   uint32_t count = 0;
283   assert(wpi_list);
284   *location = wpi_list;
285 
286   if (nth == 0) {
287     nth = MuxImageCount(*wpi_list, WEBP_CHUNK_NIL);
288     if (nth == 0) return 0;  // Not found.
289   }
290 
291   while (*wpi_list != NULL) {
292     WebPMuxImage* const cur_wpi = *wpi_list;
293     ++count;
294     if (count == nth) return 1;  // Found.
295     wpi_list = &cur_wpi->next_;
296     *location = wpi_list;
297   }
298   return 0;  // Not found.
299 }
300 
301 //------------------------------------------------------------------------------
302 // MuxImage writer methods.
303 
MuxImagePush(const WebPMuxImage * wpi,WebPMuxImage ** wpi_list)304 WebPMuxError MuxImagePush(const WebPMuxImage* wpi, WebPMuxImage** wpi_list) {
305   WebPMuxImage* new_wpi;
306 
307   while (*wpi_list != NULL) {
308     WebPMuxImage* const cur_wpi = *wpi_list;
309     if (cur_wpi->next_ == NULL) break;
310     wpi_list = &cur_wpi->next_;
311   }
312 
313   new_wpi = (WebPMuxImage*)WebPSafeMalloc(1ULL, sizeof(*new_wpi));
314   if (new_wpi == NULL) return WEBP_MUX_MEMORY_ERROR;
315   *new_wpi = *wpi;
316   new_wpi->next_ = NULL;
317 
318   if (*wpi_list != NULL) {
319     (*wpi_list)->next_ = new_wpi;
320   } else {
321     *wpi_list = new_wpi;
322   }
323   return WEBP_MUX_OK;
324 }
325 
326 //------------------------------------------------------------------------------
327 // MuxImage deletion methods.
328 
MuxImageDelete(WebPMuxImage * const wpi)329 WebPMuxImage* MuxImageDelete(WebPMuxImage* const wpi) {
330   // Delete the components of wpi. If wpi is NULL this is a noop.
331   WebPMuxImage* const next = MuxImageRelease(wpi);
332   WebPSafeFree(wpi);
333   return next;
334 }
335 
MuxImageDeleteNth(WebPMuxImage ** wpi_list,uint32_t nth)336 WebPMuxError MuxImageDeleteNth(WebPMuxImage** wpi_list, uint32_t nth) {
337   assert(wpi_list);
338   if (!SearchImageToGetOrDelete(wpi_list, nth, &wpi_list)) {
339     return WEBP_MUX_NOT_FOUND;
340   }
341   *wpi_list = MuxImageDelete(*wpi_list);
342   return WEBP_MUX_OK;
343 }
344 
345 //------------------------------------------------------------------------------
346 // MuxImage reader methods.
347 
MuxImageGetNth(const WebPMuxImage ** wpi_list,uint32_t nth,WebPMuxImage ** wpi)348 WebPMuxError MuxImageGetNth(const WebPMuxImage** wpi_list, uint32_t nth,
349                             WebPMuxImage** wpi) {
350   assert(wpi_list);
351   assert(wpi);
352   if (!SearchImageToGetOrDelete((WebPMuxImage**)wpi_list, nth,
353                                 (WebPMuxImage***)&wpi_list)) {
354     return WEBP_MUX_NOT_FOUND;
355   }
356   *wpi = (WebPMuxImage*)*wpi_list;
357   return WEBP_MUX_OK;
358 }
359 
360 //------------------------------------------------------------------------------
361 // MuxImage serialization methods.
362 
363 // Size of an image.
MuxImageDiskSize(const WebPMuxImage * const wpi)364 size_t MuxImageDiskSize(const WebPMuxImage* const wpi) {
365   size_t size = 0;
366   if (wpi->header_ != NULL) size += ChunkDiskSize(wpi->header_);
367   if (wpi->alpha_ != NULL) size += ChunkDiskSize(wpi->alpha_);
368   if (wpi->img_ != NULL) size += ChunkDiskSize(wpi->img_);
369   if (wpi->unknown_ != NULL) size += ChunkListDiskSize(wpi->unknown_);
370   return size;
371 }
372 
373 // Special case as ANMF chunk encapsulates other image chunks.
ChunkEmitSpecial(const WebPChunk * const header,size_t total_size,uint8_t * dst)374 static uint8_t* ChunkEmitSpecial(const WebPChunk* const header,
375                                  size_t total_size, uint8_t* dst) {
376   const size_t header_size = header->data_.size;
377   const size_t offset_to_next = total_size - CHUNK_HEADER_SIZE;
378   assert(header->tag_ == kChunks[IDX_ANMF].tag);
379   PutLE32(dst + 0, header->tag_);
380   PutLE32(dst + TAG_SIZE, (uint32_t)offset_to_next);
381   assert(header_size == (uint32_t)header_size);
382   memcpy(dst + CHUNK_HEADER_SIZE, header->data_.bytes, header_size);
383   if (header_size & 1) {
384     dst[CHUNK_HEADER_SIZE + header_size] = 0;  // Add padding.
385   }
386   return dst + ChunkDiskSize(header);
387 }
388 
MuxImageEmit(const WebPMuxImage * const wpi,uint8_t * dst)389 uint8_t* MuxImageEmit(const WebPMuxImage* const wpi, uint8_t* dst) {
390   // Ordering of chunks to be emitted is strictly as follows:
391   // 1. ANMF chunk (if present).
392   // 2. ALPH chunk (if present).
393   // 3. VP8/VP8L chunk.
394   assert(wpi);
395   if (wpi->header_ != NULL) {
396     dst = ChunkEmitSpecial(wpi->header_, MuxImageDiskSize(wpi), dst);
397   }
398   if (wpi->alpha_ != NULL) dst = ChunkEmit(wpi->alpha_, dst);
399   if (wpi->img_ != NULL) dst = ChunkEmit(wpi->img_, dst);
400   if (wpi->unknown_ != NULL) dst = ChunkListEmit(wpi->unknown_, dst);
401   return dst;
402 }
403 
404 //------------------------------------------------------------------------------
405 // Helper methods for mux.
406 
MuxHasAlpha(const WebPMuxImage * images)407 int MuxHasAlpha(const WebPMuxImage* images) {
408   while (images != NULL) {
409     if (images->has_alpha_) return 1;
410     images = images->next_;
411   }
412   return 0;
413 }
414 
MuxEmitRiffHeader(uint8_t * const data,size_t size)415 uint8_t* MuxEmitRiffHeader(uint8_t* const data, size_t size) {
416   PutLE32(data + 0, MKFOURCC('R', 'I', 'F', 'F'));
417   PutLE32(data + TAG_SIZE, (uint32_t)size - CHUNK_HEADER_SIZE);
418   assert(size == (uint32_t)size);
419   PutLE32(data + TAG_SIZE + CHUNK_SIZE_BYTES, MKFOURCC('W', 'E', 'B', 'P'));
420   return data + RIFF_HEADER_SIZE;
421 }
422 
MuxGetChunkListFromId(const WebPMux * mux,WebPChunkId id)423 WebPChunk** MuxGetChunkListFromId(const WebPMux* mux, WebPChunkId id) {
424   assert(mux != NULL);
425   switch (id) {
426     case WEBP_CHUNK_VP8X:    return (WebPChunk**)&mux->vp8x_;
427     case WEBP_CHUNK_ICCP:    return (WebPChunk**)&mux->iccp_;
428     case WEBP_CHUNK_ANIM:    return (WebPChunk**)&mux->anim_;
429     case WEBP_CHUNK_EXIF:    return (WebPChunk**)&mux->exif_;
430     case WEBP_CHUNK_XMP:     return (WebPChunk**)&mux->xmp_;
431     default:                 return (WebPChunk**)&mux->unknown_;
432   }
433 }
434 
IsNotCompatible(int feature,int num_items)435 static int IsNotCompatible(int feature, int num_items) {
436   return (feature != 0) != (num_items > 0);
437 }
438 
439 #define NO_FLAG ((WebPFeatureFlags)0)
440 
441 // Test basic constraints:
442 // retrieval, maximum number of chunks by index (use -1 to skip)
443 // and feature incompatibility (use NO_FLAG to skip).
444 // On success returns WEBP_MUX_OK and stores the chunk count in *num.
ValidateChunk(const WebPMux * const mux,CHUNK_INDEX idx,WebPFeatureFlags feature,uint32_t vp8x_flags,int max,int * num)445 static WebPMuxError ValidateChunk(const WebPMux* const mux, CHUNK_INDEX idx,
446                                   WebPFeatureFlags feature,
447                                   uint32_t vp8x_flags,
448                                   int max, int* num) {
449   const WebPMuxError err =
450       WebPMuxNumChunks(mux, kChunks[idx].id, num);
451   if (err != WEBP_MUX_OK) return err;
452   if (max > -1 && *num > max) return WEBP_MUX_INVALID_ARGUMENT;
453   if (feature != NO_FLAG && IsNotCompatible(vp8x_flags & feature, *num)) {
454     return WEBP_MUX_INVALID_ARGUMENT;
455   }
456   return WEBP_MUX_OK;
457 }
458 
MuxValidate(const WebPMux * const mux)459 WebPMuxError MuxValidate(const WebPMux* const mux) {
460   int num_iccp;
461   int num_exif;
462   int num_xmp;
463   int num_anim;
464   int num_frames;
465   int num_vp8x;
466   int num_images;
467   int num_alpha;
468   uint32_t flags;
469   WebPMuxError err;
470 
471   // Verify mux is not NULL.
472   if (mux == NULL) return WEBP_MUX_INVALID_ARGUMENT;
473 
474   // Verify mux has at least one image.
475   if (mux->images_ == NULL) return WEBP_MUX_INVALID_ARGUMENT;
476 
477   err = WebPMuxGetFeatures(mux, &flags);
478   if (err != WEBP_MUX_OK) return err;
479 
480   // At most one color profile chunk.
481   err = ValidateChunk(mux, IDX_ICCP, ICCP_FLAG, flags, 1, &num_iccp);
482   if (err != WEBP_MUX_OK) return err;
483 
484   // At most one EXIF metadata.
485   err = ValidateChunk(mux, IDX_EXIF, EXIF_FLAG, flags, 1, &num_exif);
486   if (err != WEBP_MUX_OK) return err;
487 
488   // At most one XMP metadata.
489   err = ValidateChunk(mux, IDX_XMP, XMP_FLAG, flags, 1, &num_xmp);
490   if (err != WEBP_MUX_OK) return err;
491 
492   // Animation: ANIMATION_FLAG, ANIM chunk and ANMF chunk(s) are consistent.
493   // At most one ANIM chunk.
494   err = ValidateChunk(mux, IDX_ANIM, NO_FLAG, flags, 1, &num_anim);
495   if (err != WEBP_MUX_OK) return err;
496   err = ValidateChunk(mux, IDX_ANMF, NO_FLAG, flags, -1, &num_frames);
497   if (err != WEBP_MUX_OK) return err;
498 
499   {
500     const int has_animation = !!(flags & ANIMATION_FLAG);
501     if (has_animation && (num_anim == 0 || num_frames == 0)) {
502       return WEBP_MUX_INVALID_ARGUMENT;
503     }
504     if (!has_animation && (num_anim == 1 || num_frames > 0)) {
505       return WEBP_MUX_INVALID_ARGUMENT;
506     }
507     if (!has_animation) {
508       const WebPMuxImage* images = mux->images_;
509       // There can be only one image.
510       if (images == NULL || images->next_ != NULL) {
511         return WEBP_MUX_INVALID_ARGUMENT;
512       }
513       // Size must match.
514       if (mux->canvas_width_ > 0) {
515         if (images->width_ != mux->canvas_width_ ||
516             images->height_ != mux->canvas_height_) {
517           return WEBP_MUX_INVALID_ARGUMENT;
518         }
519       }
520     }
521   }
522 
523   // Verify either VP8X chunk is present OR there is only one elem in
524   // mux->images_.
525   err = ValidateChunk(mux, IDX_VP8X, NO_FLAG, flags, 1, &num_vp8x);
526   if (err != WEBP_MUX_OK) return err;
527   err = ValidateChunk(mux, IDX_VP8, NO_FLAG, flags, -1, &num_images);
528   if (err != WEBP_MUX_OK) return err;
529   if (num_vp8x == 0 && num_images != 1) return WEBP_MUX_INVALID_ARGUMENT;
530 
531   // ALPHA_FLAG & alpha chunk(s) are consistent.
532   // Note: ALPHA_FLAG can be set when there is actually no Alpha data present.
533   if (MuxHasAlpha(mux->images_)) {
534     if (num_vp8x > 0) {
535       // VP8X chunk is present, so it should contain ALPHA_FLAG.
536       if (!(flags & ALPHA_FLAG)) return WEBP_MUX_INVALID_ARGUMENT;
537     } else {
538       // VP8X chunk is not present, so ALPH chunks should NOT be present either.
539       err = WebPMuxNumChunks(mux, WEBP_CHUNK_ALPHA, &num_alpha);
540       if (err != WEBP_MUX_OK) return err;
541       if (num_alpha > 0) return WEBP_MUX_INVALID_ARGUMENT;
542     }
543   }
544 
545   return WEBP_MUX_OK;
546 }
547 
548 #undef NO_FLAG
549 
550 //------------------------------------------------------------------------------
551 
552