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src/Source/LibWebP/src/enc/backward_references.h  view on Meta::CPAN

// -----------------------------------------------------------------------------
// VP8LHashChain

#define HASH_BITS 18
#define HASH_SIZE (1 << HASH_BITS)

typedef struct VP8LHashChain VP8LHashChain;
struct VP8LHashChain {
  // Stores the most recently added position with the given hash value.
  int32_t hash_to_first_index_[HASH_SIZE];
  // chain_[pos] stores the previous position with the same hash value
  // for every pixel in the image.
  int32_t* chain_;
  // This is the maximum size of the hash_chain that can be constructed.
  // Typically this is the pixel count (width x height) for a given image.
  int size_;
};

// Must be called first, to set size.
int VP8LHashChainInit(VP8LHashChain* const p, int size);
void VP8LHashChainClear(VP8LHashChain* const p);  // release memory

// -----------------------------------------------------------------------------
// VP8LBackwardRefs (block-based backward-references storage)

// maximum number of reference blocks the image will be segmented into
#define MAX_REFS_BLOCK_PER_IMAGE 16

typedef struct PixOrCopyBlock PixOrCopyBlock;   // forward declaration
typedef struct VP8LBackwardRefs VP8LBackwardRefs;

// Container for blocks chain
struct VP8LBackwardRefs {
  int block_size_;               // common block-size
  int error_;                    // set to true if some memory error occurred
  PixOrCopyBlock* refs_;         // list of currently used blocks
  PixOrCopyBlock** tail_;        // for list recycling
  PixOrCopyBlock* free_blocks_;  // free-list
  PixOrCopyBlock* last_block_;   // used for adding new refs (internal)
};

// Initialize the object. 'block_size' is the common block size to store
// references (typically, width * height / MAX_REFS_BLOCK_PER_IMAGE).
void VP8LBackwardRefsInit(VP8LBackwardRefs* const refs, int block_size);
// Release memory for backward references.
void VP8LBackwardRefsClear(VP8LBackwardRefs* const refs);
// Copies the 'src' backward refs to the 'dst'. Returns 0 in case of error.
int VP8LBackwardRefsCopy(const VP8LBackwardRefs* const src,
                         VP8LBackwardRefs* const dst);

// Cursor for iterating on references content
typedef struct {
  // public:
  PixOrCopy* cur_pos;           // current position
  // private:
  PixOrCopyBlock* cur_block_;   // current block in the refs list
  const PixOrCopy* last_pos_;   // sentinel for switching to next block
} VP8LRefsCursor;

// Returns a cursor positioned at the beginning of the references list.
VP8LRefsCursor VP8LRefsCursorInit(const VP8LBackwardRefs* const refs);
// Returns true if cursor is pointing at a valid position.
static WEBP_INLINE int VP8LRefsCursorOk(const VP8LRefsCursor* const c) {
  return (c->cur_pos != NULL);
}
// Move to next block of references. Internal, not to be called directly.
void VP8LRefsCursorNextBlock(VP8LRefsCursor* const c);
// Move to next position, or NULL. Should not be called if !VP8LRefsCursorOk().
static WEBP_INLINE void VP8LRefsCursorNext(VP8LRefsCursor* const c) {
  assert(c != NULL);
  assert(VP8LRefsCursorOk(c));
  if (++c->cur_pos == c->last_pos_) VP8LRefsCursorNextBlock(c);
}

// -----------------------------------------------------------------------------
// Main entry points

// Evaluates best possible backward references for specified quality.
// The input cache_bits to 'VP8LGetBackwardReferences' sets the maximum cache
// bits to use (passing 0 implies disabling the local color cache).
// The optimal cache bits is evaluated and set for the *cache_bits parameter.
// The return value is the pointer to the best of the two backward refs viz,
// refs[0] or refs[1].
VP8LBackwardRefs* VP8LGetBackwardReferences(
    int width, int height, const uint32_t* const argb, int quality,
    int low_effort, int* const cache_bits, VP8LHashChain* const hash_chain,
    VP8LBackwardRefs refs[2]);

#ifdef __cplusplus
}
#endif

#endif  // WEBP_ENC_BACKWARD_REFERENCES_H_