1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
|
// Copyright 2011 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
// Alpha-plane decompression.
//
// Author: Skal (pascal.massimino@gmail.com)
#include <stdlib.h>
#include "./alphai.h"
#include "./vp8i.h"
#include "./vp8li.h"
#include "../dsp/dsp.h"
#include "../utils/quant_levels_dec.h"
#include "../utils/utils.h"
#include "../webp/format_constants.h"
//------------------------------------------------------------------------------
// ALPHDecoder object.
// Allocates a new alpha decoder instance.
static ALPHDecoder* ALPHNew(void) {
ALPHDecoder* const dec = (ALPHDecoder*)WebPSafeCalloc(1ULL, sizeof(*dec));
return dec;
}
// Clears and deallocates an alpha decoder instance.
static void ALPHDelete(ALPHDecoder* const dec) {
if (dec != NULL) {
VP8LDelete(dec->vp8l_dec_);
dec->vp8l_dec_ = NULL;
WebPSafeFree(dec);
}
}
//------------------------------------------------------------------------------
// Decoding.
// Initialize alpha decoding by parsing the alpha header and decoding the image
// header for alpha data stored using lossless compression.
// Returns false in case of error in alpha header (data too short, invalid
// compression method or filter, error in lossless header data etc).
static int ALPHInit(ALPHDecoder* const dec, const uint8_t* data,
size_t data_size, const VP8Io* const src_io,
uint8_t* output) {
int ok = 0;
const uint8_t* const alpha_data = data + ALPHA_HEADER_LEN;
const size_t alpha_data_size = data_size - ALPHA_HEADER_LEN;
int rsrv;
VP8Io* const io = &dec->io_;
assert(data != NULL && output != NULL && src_io != NULL);
VP8FiltersInit();
dec->output_ = output;
dec->width_ = src_io->width;
dec->height_ = src_io->height;
assert(dec->width_ > 0 && dec->height_ > 0);
if (data_size <= ALPHA_HEADER_LEN) {
return 0;
}
dec->method_ = (data[0] >> 0) & 0x03;
dec->filter_ = (data[0] >> 2) & 0x03;
dec->pre_processing_ = (data[0] >> 4) & 0x03;
rsrv = (data[0] >> 6) & 0x03;
if (dec->method_ < ALPHA_NO_COMPRESSION ||
dec->method_ > ALPHA_LOSSLESS_COMPRESSION ||
dec->filter_ >= WEBP_FILTER_LAST ||
dec->pre_processing_ > ALPHA_PREPROCESSED_LEVELS ||
rsrv != 0) {
return 0;
}
// Copy the necessary parameters from src_io to io
VP8InitIo(io);
WebPInitCustomIo(NULL, io);
io->opaque = dec;
io->width = src_io->width;
io->height = src_io->height;
io->use_cropping = src_io->use_cropping;
io->crop_left = src_io->crop_left;
io->crop_right = src_io->crop_right;
io->crop_top = src_io->crop_top;
io->crop_bottom = src_io->crop_bottom;
// No need to copy the scaling parameters.
if (dec->method_ == ALPHA_NO_COMPRESSION) {
const size_t alpha_decoded_size = dec->width_ * dec->height_;
ok = (alpha_data_size >= alpha_decoded_size);
} else {
assert(dec->method_ == ALPHA_LOSSLESS_COMPRESSION);
ok = VP8LDecodeAlphaHeader(dec, alpha_data, alpha_data_size);
}
return ok;
}
// Decodes, unfilters and dequantizes *at least* 'num_rows' rows of alpha
// starting from row number 'row'. It assumes that rows up to (row - 1) have
// already been decoded.
// Returns false in case of bitstream error.
static int ALPHDecode(VP8Decoder* const dec, int row, int num_rows) {
ALPHDecoder* const alph_dec = dec->alph_dec_;
const int width = alph_dec->width_;
const int height = alph_dec->io_.crop_bottom;
if (alph_dec->method_ == ALPHA_NO_COMPRESSION) {
int y;
const uint8_t* prev_line = dec->alpha_prev_line_;
const uint8_t* deltas = dec->alpha_data_ + ALPHA_HEADER_LEN + row * width;
uint8_t* dst = dec->alpha_plane_ + row * width;
assert(deltas <= &dec->alpha_data_[dec->alpha_data_size_]);
if (alph_dec->filter_ != WEBP_FILTER_NONE) {
assert(WebPUnfilters[alph_dec->filter_] != NULL);
for (y = 0; y < num_rows; ++y) {
WebPUnfilters[alph_dec->filter_](prev_line, deltas, dst, width);
prev_line = dst;
dst += width;
deltas += width;
}
} else {
for (y = 0; y < num_rows; ++y) {
memcpy(dst, deltas, width * sizeof(*dst));
prev_line = dst;
dst += width;
deltas += width;
}
}
dec->alpha_prev_line_ = prev_line;
} else { // alph_dec->method_ == ALPHA_LOSSLESS_COMPRESSION
assert(alph_dec->vp8l_dec_ != NULL);
if (!VP8LDecodeAlphaImageStream(alph_dec, row + num_rows)) {
return 0;
}
}
if (row + num_rows >= height) {
dec->is_alpha_decoded_ = 1;
}
return 1;
}
static int AllocateAlphaPlane(VP8Decoder* const dec, const VP8Io* const io) {
const int stride = io->width;
const int height = io->crop_bottom;
const uint64_t alpha_size = (uint64_t)stride * height;
assert(dec->alpha_plane_mem_ == NULL);
dec->alpha_plane_mem_ =
(uint8_t*)WebPSafeMalloc(alpha_size, sizeof(*dec->alpha_plane_));
if (dec->alpha_plane_mem_ == NULL) {
return 0;
}
dec->alpha_plane_ = dec->alpha_plane_mem_;
dec->alpha_prev_line_ = NULL;
return 1;
}
void WebPDeallocateAlphaMemory(VP8Decoder* const dec) {
assert(dec != NULL);
WebPSafeFree(dec->alpha_plane_mem_);
dec->alpha_plane_mem_ = NULL;
dec->alpha_plane_ = NULL;
ALPHDelete(dec->alph_dec_);
dec->alph_dec_ = NULL;
}
//------------------------------------------------------------------------------
// Main entry point.
const uint8_t* VP8DecompressAlphaRows(VP8Decoder* const dec,
const VP8Io* const io,
int row, int num_rows) {
const int width = io->width;
const int height = io->crop_bottom;
assert(dec != NULL && io != NULL);
if (row < 0 || num_rows <= 0 || row + num_rows > height) {
return NULL; // sanity check.
}
if (!dec->is_alpha_decoded_) {
if (dec->alph_dec_ == NULL) { // Initialize decoder.
dec->alph_dec_ = ALPHNew();
if (dec->alph_dec_ == NULL) return NULL;
if (!AllocateAlphaPlane(dec, io)) goto Error;
if (!ALPHInit(dec->alph_dec_, dec->alpha_data_, dec->alpha_data_size_,
io, dec->alpha_plane_)) {
goto Error;
}
// if we allowed use of alpha dithering, check whether it's needed at all
if (dec->alph_dec_->pre_processing_ != ALPHA_PREPROCESSED_LEVELS) {
dec->alpha_dithering_ = 0; // disable dithering
} else {
num_rows = height - row; // decode everything in one pass
}
}
assert(dec->alph_dec_ != NULL);
assert(row + num_rows <= height);
if (!ALPHDecode(dec, row, num_rows)) goto Error;
if (dec->is_alpha_decoded_) { // finished?
ALPHDelete(dec->alph_dec_);
dec->alph_dec_ = NULL;
if (dec->alpha_dithering_ > 0) {
uint8_t* const alpha = dec->alpha_plane_ + io->crop_top * width
+ io->crop_left;
if (!WebPDequantizeLevels(alpha,
io->crop_right - io->crop_left,
io->crop_bottom - io->crop_top,
width, dec->alpha_dithering_)) {
goto Error;
}
}
}
}
// Return a pointer to the current decoded row.
return dec->alpha_plane_ + row * width;
Error:
WebPDeallocateAlphaMemory(dec);
return NULL;
}
|