backward_references_enc.h revision fa39824bb690c5806358871f46940d0450973d8a 
1// Copyright 2012 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// Author: Jyrki Alakuijala (jyrki@google.com)
11//
12
13#ifndef WEBP_ENC_BACKWARD_REFERENCES_H_
14#define WEBP_ENC_BACKWARD_REFERENCES_H_
15
16#include <assert.h>
17#include <stdlib.h>
18#include "../webp/types.h"
19#include "../webp/format_constants.h"
20
21#ifdef __cplusplus
22extern "C" {
23#endif
24
25// The maximum allowed limit is 11.
26#define MAX_COLOR_CACHE_BITS 10
27
28// -----------------------------------------------------------------------------
29// PixOrCopy
30
31enum Mode {
32  kLiteral,
33  kCacheIdx,
34  kCopy,
35  kNone
36};
37
38typedef struct {
39  // mode as uint8_t to make the memory layout to be exactly 8 bytes.
40  uint8_t mode;
41  uint16_t len;
42  uint32_t argb_or_distance;
43} PixOrCopy;
44
45static WEBP_INLINE PixOrCopy PixOrCopyCreateCopy(uint32_t distance,
46                                                 uint16_t len) {
47  PixOrCopy retval;
48  retval.mode = kCopy;
49  retval.argb_or_distance = distance;
50  retval.len = len;
51  return retval;
52}
53
54static WEBP_INLINE PixOrCopy PixOrCopyCreateCacheIdx(int idx) {
55  PixOrCopy retval;
56  assert(idx >= 0);
57  assert(idx < (1 << MAX_COLOR_CACHE_BITS));
58  retval.mode = kCacheIdx;
59  retval.argb_or_distance = idx;
60  retval.len = 1;
61  return retval;
62}
63
64static WEBP_INLINE PixOrCopy PixOrCopyCreateLiteral(uint32_t argb) {
65  PixOrCopy retval;
66  retval.mode = kLiteral;
67  retval.argb_or_distance = argb;
68  retval.len = 1;
69  return retval;
70}
71
72static WEBP_INLINE int PixOrCopyIsLiteral(const PixOrCopy* const p) {
73  return (p->mode == kLiteral);
74}
75
76static WEBP_INLINE int PixOrCopyIsCacheIdx(const PixOrCopy* const p) {
77  return (p->mode == kCacheIdx);
78}
79
80static WEBP_INLINE int PixOrCopyIsCopy(const PixOrCopy* const p) {
81  return (p->mode == kCopy);
82}
83
84static WEBP_INLINE uint32_t PixOrCopyLiteral(const PixOrCopy* const p,
85                                             int component) {
86  assert(p->mode == kLiteral);
87  return (p->argb_or_distance >> (component * 8)) & 0xff;
88}
89
90static WEBP_INLINE uint32_t PixOrCopyLength(const PixOrCopy* const p) {
91  return p->len;
92}
93
94static WEBP_INLINE uint32_t PixOrCopyArgb(const PixOrCopy* const p) {
95  assert(p->mode == kLiteral);
96  return p->argb_or_distance;
97}
98
99static WEBP_INLINE uint32_t PixOrCopyCacheIdx(const PixOrCopy* const p) {
100  assert(p->mode == kCacheIdx);
101  assert(p->argb_or_distance < (1U << MAX_COLOR_CACHE_BITS));
102  return p->argb_or_distance;
103}
104
105static WEBP_INLINE uint32_t PixOrCopyDistance(const PixOrCopy* const p) {
106  assert(p->mode == kCopy);
107  return p->argb_or_distance;
108}
109
110// -----------------------------------------------------------------------------
111// VP8LHashChain
112
113#define HASH_BITS 18
114#define HASH_SIZE (1 << HASH_BITS)
115
116typedef struct VP8LHashChain VP8LHashChain;
117struct VP8LHashChain {
118  // The 20 most significant bits contain the offset at which the best match
119  // is found. These 20 bits are the limit defined by GetWindowSizeForHashChain
120  // (through WINDOW_SIZE = 1<<20).
121  // The lower 12 bits contain the length of the match. The 12 bit limit is
122  // defined in MaxFindCopyLength with MAX_LENGTH=4096.
123  uint32_t* offset_length_;
124  // This is the maximum size of the hash_chain that can be constructed.
125  // Typically this is the pixel count (width x height) for a given image.
126  int size_;
127};
128
129// Must be called first, to set size.
130int VP8LHashChainInit(VP8LHashChain* const p, int size);
131// Pre-compute the best matches for argb.
132int VP8LHashChainFill(VP8LHashChain* const p, int quality,
133                      const uint32_t* const argb, int xsize, int ysize,
134                      int low_effort);
135void VP8LHashChainClear(VP8LHashChain* const p);  // release memory
136
137// -----------------------------------------------------------------------------
138// VP8LBackwardRefs (block-based backward-references storage)
139
140// maximum number of reference blocks the image will be segmented into
141#define MAX_REFS_BLOCK_PER_IMAGE 16
142
143typedef struct PixOrCopyBlock PixOrCopyBlock;   // forward declaration
144typedef struct VP8LBackwardRefs VP8LBackwardRefs;
145
146// Container for blocks chain
147struct VP8LBackwardRefs {
148  int block_size_;               // common block-size
149  int error_;                    // set to true if some memory error occurred
150  PixOrCopyBlock* refs_;         // list of currently used blocks
151  PixOrCopyBlock** tail_;        // for list recycling
152  PixOrCopyBlock* free_blocks_;  // free-list
153  PixOrCopyBlock* last_block_;   // used for adding new refs (internal)
154};
155
156// Initialize the object. 'block_size' is the common block size to store
157// references (typically, width * height / MAX_REFS_BLOCK_PER_IMAGE).
158void VP8LBackwardRefsInit(VP8LBackwardRefs* const refs, int block_size);
159// Release memory for backward references.
160void VP8LBackwardRefsClear(VP8LBackwardRefs* const refs);
161// Copies the 'src' backward refs to the 'dst'. Returns 0 in case of error.
162int VP8LBackwardRefsCopy(const VP8LBackwardRefs* const src,
163                         VP8LBackwardRefs* const dst);
164
165// Cursor for iterating on references content
166typedef struct {
167  // public:
168  PixOrCopy* cur_pos;           // current position
169  // private:
170  PixOrCopyBlock* cur_block_;   // current block in the refs list
171  const PixOrCopy* last_pos_;   // sentinel for switching to next block
172} VP8LRefsCursor;
173
174// Returns a cursor positioned at the beginning of the references list.
175VP8LRefsCursor VP8LRefsCursorInit(const VP8LBackwardRefs* const refs);
176// Returns true if cursor is pointing at a valid position.
177static WEBP_INLINE int VP8LRefsCursorOk(const VP8LRefsCursor* const c) {
178  return (c->cur_pos != NULL);
179}
180// Move to next block of references. Internal, not to be called directly.
181void VP8LRefsCursorNextBlock(VP8LRefsCursor* const c);
182// Move to next position, or NULL. Should not be called if !VP8LRefsCursorOk().
183static WEBP_INLINE void VP8LRefsCursorNext(VP8LRefsCursor* const c) {
184  assert(c != NULL);
185  assert(VP8LRefsCursorOk(c));
186  if (++c->cur_pos == c->last_pos_) VP8LRefsCursorNextBlock(c);
187}
188
189// -----------------------------------------------------------------------------
190// Main entry points
191
192// Evaluates best possible backward references for specified quality.
193// The input cache_bits to 'VP8LGetBackwardReferences' sets the maximum cache
194// bits to use (passing 0 implies disabling the local color cache).
195// The optimal cache bits is evaluated and set for the *cache_bits parameter.
196// The return value is the pointer to the best of the two backward refs viz,
197// refs[0] or refs[1].
198VP8LBackwardRefs* VP8LGetBackwardReferences(
199    int width, int height, const uint32_t* const argb, int quality,
200    int low_effort, int* const cache_bits,
201    const VP8LHashChain* const hash_chain, VP8LBackwardRefs refs[2]);
202
203#ifdef __cplusplus
204}
205#endif
206
207#endif  // WEBP_ENC_BACKWARD_REFERENCES_H_
208