IDX_ALPHA         258 3rdparty/libwebp/mux/muxedit.c     err = AddDataToChunkList(&alpha, copy_data, kChunks[IDX_ALPHA].tag,
IDX_ALPHA         559 3rdparty/libwebp/mux/muxinternal.c       err = ValidateChunk(mux, IDX_ALPHA, ALPHA_FLAG, flags, -1, &num_alpha);