mirror of
https://github.com/webmproject/libwebp.git
synced 2024-11-20 12:28:26 +01:00
2ab4b72f53
This is a (minor) bitstream change: if the 'color_space' bit is set to '1' (which is normally an undefined/invalid behaviour), we add extra data at the end of partition #0 (so-called 'extensions') Namely, we add the size of the extension data as 3 bytes (little-endian), followed by a set of bits telling which extensions we're incorporating. The data then _preceeds_ this trailing tags. This is all experimental, and you'll need to have '#define WEBP_EXPERIMENTAL_FEATURES' in webp/types.h to enable this code (at your own risk! :)) Still, this hack produces almost-valid WebP file for decoders that don't check this color_space bit. In particular, previous 'dwebp' (and for instance Chrome) will recognize this files and decode them, but without the alpha of course. Other decoder will just see random extra stuff at the end of partition #0. To experiment with the alpha-channel, you need to compile on Unix platform and use PNGs for input/output. If 'alpha.png' is a source with alpha channel, then you can try (on Unix): cwebp alpha.png -o alpha.webp dwebp alpha.webp -o test.png cwebp now has a '-noalpha' flag to ignore any alpha information from the source, if present. More hacking and experimenting welcome! Change-Id: I3c7b1fd8411c9e7a9f77690e898479ad85c52f3e
64 lines
2.0 KiB
C
64 lines
2.0 KiB
C
// Copyright 2011 Google Inc.
|
|
//
|
|
// This code is licensed under the same terms as WebM:
|
|
// Software License Agreement: http://www.webmproject.org/license/software/
|
|
// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
|
|
// -----------------------------------------------------------------------------
|
|
//
|
|
// Bit writing and boolean coder
|
|
//
|
|
// Author: Skal (pascal.massimino@gmail.com)
|
|
|
|
#ifndef WEBP_ENC_BIT_WRITER_H_
|
|
#define WEBP_ENC_BIT_WRITER_H_
|
|
|
|
#include "vp8enci.h"
|
|
|
|
#if defined(__cplusplus) || defined(c_plusplus)
|
|
extern "C" {
|
|
#endif
|
|
|
|
//-----------------------------------------------------------------------------
|
|
// Bit-writing
|
|
|
|
typedef struct VP8BitWriter VP8BitWriter;
|
|
struct VP8BitWriter {
|
|
int32_t range_; // range-1
|
|
int32_t value_;
|
|
int run_; // number of outstanding bits
|
|
int nb_bits_; // number of pending bits
|
|
uint8_t* buf_;
|
|
size_t pos_;
|
|
size_t max_pos_;
|
|
int error_; // true in case of error
|
|
};
|
|
|
|
int VP8BitWriterInit(VP8BitWriter* const bw, size_t expected_size);
|
|
uint8_t* VP8BitWriterFinish(VP8BitWriter* const bw);
|
|
int VP8PutBit(VP8BitWriter* const bw, int bit, int prob);
|
|
int VP8PutBitUniform(VP8BitWriter* const bw, int bit);
|
|
void VP8PutValue(VP8BitWriter* const bw, int value, int nb_bits);
|
|
void VP8PutSignedValue(VP8BitWriter* const bw, int value, int nb_bits);
|
|
int VP8BitWriterAppend(VP8BitWriter* const bw,
|
|
const uint8_t* data, size_t size);
|
|
|
|
// return approximate write position (in bits)
|
|
static inline uint64_t VP8BitWriterPos(const VP8BitWriter* const bw) {
|
|
return (uint64_t)(bw->pos_ + bw->run_) * 8 + 8 + bw->nb_bits_;
|
|
}
|
|
|
|
static inline uint8_t* VP8BitWriterBuf(const VP8BitWriter* const bw) {
|
|
return bw->buf_;
|
|
}
|
|
static inline size_t VP8BitWriterSize(const VP8BitWriter* const bw) {
|
|
return bw->pos_;
|
|
}
|
|
|
|
//-----------------------------------------------------------------------------
|
|
|
|
#if defined(__cplusplus) || defined(c_plusplus)
|
|
} // extern "C"
|
|
#endif
|
|
|
|
#endif // WEBP_ENC_BIT_WRITER_H_
|