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Mux: Allow only some frames/tiles to have alpha.

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And related const fixes.

Change-Id: I79f6f1b9f8c6faac8cc4ef24b58edff6d90de045
This commit is contained in:
Urvang Joshi 2012-06-29 17:16:08 +05:30
parent 3ba81bbe8b
commit 97649c8f6b
4 changed files with 17 additions and 26 deletions
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15
doc/webp-container-spec.txt
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@ -300,9 +300,7 @@ multiple frames. Data for each frame consists of:
present at the beginning of each tile for a frame that is represented as
multiple tile images.
* An optional 'ALPH' chunk with alpha bitstream of the frame/tile. If the
file contains transparency, this chunk MUST be present for each frame/tile
containing a 'VP8 ' chunk. It MUST NOT be present otherwise.
* An optional 'ALPH' chunk with alpha bitstream of the frame/tile.
* A 'VP8 ' or a 'VP8L' chunk containing compressed image data of the
frame/tile.
@ -355,7 +353,8 @@ Metadata (M): 1 bit
Alpha (L): 1 bit
: Set if the file contains images with transparency information ("alpha").
: Set if the file contains some (or all) images with transparency information
("alpha").
Rotation and Symmetry (R): 3 bits
@ -540,10 +539,10 @@ Alpha bitstream: _Chunk Size_ - `1` bytes
: Encoded alpha bitstream.
This optional chunk contains encoded alpha data for a single frame/tile.
Either **ALL or NONE** of the frame/tiles must contain this chunk. However,
there is one exception to this rule: a frame/tile containing a 'VP8L' chunk
SHOULD NOT contain this chunk. **Rationale**: the transparency information of
a frame/tile is already part of the 'VP8L' chunk.
For images with transparency, some of the frames/tiles may contain this chunk.
However, a frame/tile containing a 'VP8L' chunk SHOULD NOT contain this chunk.
**Rationale**: the transparency information of a frame/tile is already part of
the 'VP8L' chunk.
The alpha channel data is losslessly stored as raw data (when
compression method is '0') or compressed using the lossless format

5
src/mux/muxedit.c
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@ -613,9 +613,8 @@ static WebPMuxError CreateVP8XChunk(WebPMux* const mux) {
}
}
if (images->alpha_ != NULL && images->alpha_->data_.bytes_ != NULL) {
// This is an image with alpha channel.
flags |= ALPHA_FLAG;
if (MuxImageCount(images, WEBP_CHUNK_ALPHA) > 0) {
flags |= ALPHA_FLAG; // Some images have an alpha channel.
}
if (flags == 0) {

12
src/mux/muxi.h
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@ -194,7 +194,7 @@ WebPMuxImage* MuxImageDelete(WebPMuxImage* const wpi);
void MuxImageDeleteAll(WebPMuxImage** const wpi_list);
// Count number of images matching the given tag id in the 'wpi_list'.
int MuxImageCount(WebPMuxImage* const wpi_list, WebPChunkId id);
int MuxImageCount(const WebPMuxImage* wpi_list, WebPChunkId id);
// Check if given ID corresponds to an image related chunk.
static WEBP_INLINE int IsWPI(WebPChunkId id) {
@ -208,14 +208,14 @@ static WEBP_INLINE int IsWPI(WebPChunkId id) {
}
// Get a reference to appropriate chunk list within an image given chunk tag.
static WEBP_INLINE WebPChunk** MuxImageGetListFromId(WebPMuxImage* wpi,
WebPChunkId id) {
static WEBP_INLINE WebPChunk** MuxImageGetListFromId(
const WebPMuxImage* const wpi, WebPChunkId id) {
assert(wpi != NULL);
switch (id) {
case WEBP_CHUNK_FRAME:
case WEBP_CHUNK_TILE: return &wpi->header_;
case WEBP_CHUNK_ALPHA: return &wpi->alpha_;
case WEBP_CHUNK_IMAGE: return &wpi->img_;
case WEBP_CHUNK_TILE: return (WebPChunk**)&wpi->header_;
case WEBP_CHUNK_ALPHA: return (WebPChunk**)&wpi->alpha_;
case WEBP_CHUNK_IMAGE: return (WebPChunk**)&wpi->img_;
default: return NULL;
}
}

11
src/mux/muxinternal.c
View File

@ -262,9 +262,9 @@ WebPMuxImage* MuxImageRelease(WebPMuxImage* const wpi) {
//------------------------------------------------------------------------------
// MuxImage search methods.
int MuxImageCount(WebPMuxImage* const wpi_list, WebPChunkId id) {
int MuxImageCount(const WebPMuxImage* wpi_list, WebPChunkId id) {
int count = 0;
WebPMuxImage* current;
const WebPMuxImage* current;
for (current = wpi_list; current != NULL; current = current->next_) {
const WebPChunk* const wpi_chunk = *MuxImageGetListFromId(current, id);
if (wpi_chunk != NULL) {
@ -558,13 +558,6 @@ WebPMuxError MuxValidate(const WebPMux* const mux) {
} else {
err = ValidateChunk(mux, IDX_ALPHA, ALPHA_FLAG, flags, -1, &num_alpha);
if (err != WEBP_MUX_OK) return err;
// num_images & num_alpha_chunks are consistent.
if (num_alpha > 0 && num_alpha != num_images) {
// Note that "num_alpha > 0" is the correct test but "flags && ALPHA_FLAG"
// is NOT, because ALPHA_FLAG is based on first image only.
return WEBP_MUX_INVALID_ARGUMENT;
}
}
// num_tiles & num_images are consistent.