1// Copyright 2011 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// Alpha-plane decompression.
11//
12// Author: Skal (pascal.massimino@gmail.com)
13
14#include <stdlib.h>
15#include "src/dec/alphai_dec.h"
16#include "src/dec/vp8i_dec.h"
17#include "src/dec/vp8li_dec.h"
18#include "src/dsp/dsp.h"
19#include "src/utils/quant_levels_dec_utils.h"
20#include "src/utils/utils.h"
21#include "src/webp/format_constants.h"
22
23//------------------------------------------------------------------------------
24// ALPHDecoder object.
25
26// Allocates a new alpha decoder instance.
27static ALPHDecoder* ALPHNew(void) {
28 ALPHDecoder* const dec = (ALPHDecoder*)WebPSafeCalloc(1ULL, sizeof(*dec));
29 return dec;
30}
31
32// Clears and deallocates an alpha decoder instance.
33static void ALPHDelete(ALPHDecoder* const dec) {
34 if (dec != NULL) {
35 VP8LDelete(dec->vp8l_dec_);
36 dec->vp8l_dec_ = NULL;
37 WebPSafeFree(dec);
38 }
39}
40
41//------------------------------------------------------------------------------
42// Decoding.
43
44// Initialize alpha decoding by parsing the alpha header and decoding the image
45// header for alpha data stored using lossless compression.
46// Returns false in case of error in alpha header (data too short, invalid
47// compression method or filter, error in lossless header data etc).
48static int ALPHInit(ALPHDecoder* const dec, const uint8_t* data,
49 size_t data_size, const VP8Io* const src_io,
50 uint8_t* output) {
51 int ok = 0;
52 const uint8_t* const alpha_data = data + ALPHA_HEADER_LEN;
53 const size_t alpha_data_size = data_size - ALPHA_HEADER_LEN;
54 int rsrv;
55 VP8Io* const io = &dec->io_;
56
57 assert(data != NULL && output != NULL && src_io != NULL);
58
59 VP8FiltersInit();
60 dec->output_ = output;
61 dec->width_ = src_io->width;
62 dec->height_ = src_io->height;
63 assert(dec->width_ > 0 && dec->height_ > 0);
64
65 if (data_size <= ALPHA_HEADER_LEN) {
66 return 0;
67 }
68
69 dec->method_ = (data[0] >> 0) & 0x03;
70 dec->filter_ = (WEBP_FILTER_TYPE)((data[0] >> 2) & 0x03);
71 dec->pre_processing_ = (data[0] >> 4) & 0x03;
72 rsrv = (data[0] >> 6) & 0x03;
73 if (dec->method_ < ALPHA_NO_COMPRESSION ||
74 dec->method_ > ALPHA_LOSSLESS_COMPRESSION ||
75 dec->filter_ >= WEBP_FILTER_LAST ||
76 dec->pre_processing_ > ALPHA_PREPROCESSED_LEVELS ||
77 rsrv != 0) {
78 return 0;
79 }
80
81 // Copy the necessary parameters from src_io to io
82 VP8InitIo(io);
83 WebPInitCustomIo(NULL, io);
84 io->opaque = dec;
85 io->width = src_io->width;
86 io->height = src_io->height;
87
88 io->use_cropping = src_io->use_cropping;
89 io->crop_left = src_io->crop_left;
90 io->crop_right = src_io->crop_right;
91 io->crop_top = src_io->crop_top;
92 io->crop_bottom = src_io->crop_bottom;
93 // No need to copy the scaling parameters.
94
95 if (dec->method_ == ALPHA_NO_COMPRESSION) {
96 const size_t alpha_decoded_size = dec->width_ * dec->height_;
97 ok = (alpha_data_size >= alpha_decoded_size);
98 } else {
99 assert(dec->method_ == ALPHA_LOSSLESS_COMPRESSION);
100 ok = VP8LDecodeAlphaHeader(dec, alpha_data, alpha_data_size);
101 }
102
103 return ok;
104}
105
106// Decodes, unfilters and dequantizes *at least* 'num_rows' rows of alpha
107// starting from row number 'row'. It assumes that rows up to (row - 1) have
108// already been decoded.
109// Returns false in case of bitstream error.
110static int ALPHDecode(VP8Decoder* const dec, int row, int num_rows) {
111 ALPHDecoder* const alph_dec = dec->alph_dec_;
112 const int width = alph_dec->width_;
113 const int height = alph_dec->io_.crop_bottom;
114 if (alph_dec->method_ == ALPHA_NO_COMPRESSION) {
115 int y;
116 const uint8_t* prev_line = dec->alpha_prev_line_;
117 const uint8_t* deltas = dec->alpha_data_ + ALPHA_HEADER_LEN + row * width;
118 uint8_t* dst = dec->alpha_plane_ + row * width;
119 assert(deltas <= &dec->alpha_data_[dec->alpha_data_size_]);
120 if (alph_dec->filter_ != WEBP_FILTER_NONE) {
121 assert(WebPUnfilters[alph_dec->filter_] != NULL);
122 for (y = 0; y < num_rows; ++y) {
123 WebPUnfilters[alph_dec->filter_](prev_line, deltas, dst, width);
124 prev_line = dst;
125 dst += width;
126 deltas += width;
127 }
128 } else {
129 for (y = 0; y < num_rows; ++y) {
130 memcpy(dst, deltas, width * sizeof(*dst));
131 prev_line = dst;
132 dst += width;
133 deltas += width;
134 }
135 }
136 dec->alpha_prev_line_ = prev_line;
137 } else { // alph_dec->method_ == ALPHA_LOSSLESS_COMPRESSION
138 assert(alph_dec->vp8l_dec_ != NULL);
139 if (!VP8LDecodeAlphaImageStream(alph_dec, row + num_rows)) {
140 return 0;
141 }
142 }
143
144 if (row + num_rows >= height) {
145 dec->is_alpha_decoded_ = 1;
146 }
147 return 1;
148}
149
150static int AllocateAlphaPlane(VP8Decoder* const dec, const VP8Io* const io) {
151 const int stride = io->width;
152 const int height = io->crop_bottom;
153 const uint64_t alpha_size = (uint64_t)stride * height;
154 assert(dec->alpha_plane_mem_ == NULL);
155 dec->alpha_plane_mem_ =
156 (uint8_t*)WebPSafeMalloc(alpha_size, sizeof(*dec->alpha_plane_));
157 if (dec->alpha_plane_mem_ == NULL) {
158 return 0;
159 }
160 dec->alpha_plane_ = dec->alpha_plane_mem_;
161 dec->alpha_prev_line_ = NULL;
162 return 1;
163}
164
165void WebPDeallocateAlphaMemory(VP8Decoder* const dec) {
166 assert(dec != NULL);
167 WebPSafeFree(dec->alpha_plane_mem_);
168 dec->alpha_plane_mem_ = NULL;
169 dec->alpha_plane_ = NULL;
170 ALPHDelete(dec->alph_dec_);
171 dec->alph_dec_ = NULL;
172}
173
174//------------------------------------------------------------------------------
175// Main entry point.
176
177const uint8_t* VP8DecompressAlphaRows(VP8Decoder* const dec,
178 const VP8Io* const io,
179 int row, int num_rows) {
180 const int width = io->width;
181 const int height = io->crop_bottom;
182
183 assert(dec != NULL && io != NULL);
184
185 if (row < 0 || num_rows <= 0 || row + num_rows > height) {
186 return NULL; // sanity check.
187 }
188
189 if (!dec->is_alpha_decoded_) {
190 if (dec->alph_dec_ == NULL) { // Initialize decoder.
191 dec->alph_dec_ = ALPHNew();
192 if (dec->alph_dec_ == NULL) return NULL;
193 if (!AllocateAlphaPlane(dec, io)) goto Error;
194 if (!ALPHInit(dec->alph_dec_, dec->alpha_data_, dec->alpha_data_size_,
195 io, dec->alpha_plane_)) {
196 goto Error;
197 }
198 // if we allowed use of alpha dithering, check whether it's needed at all
199 if (dec->alph_dec_->pre_processing_ != ALPHA_PREPROCESSED_LEVELS) {
200 dec->alpha_dithering_ = 0; // disable dithering
201 } else {
202 num_rows = height - row; // decode everything in one pass
203 }
204 }
205
206 assert(dec->alph_dec_ != NULL);
207 assert(row + num_rows <= height);
208 if (!ALPHDecode(dec, row, num_rows)) goto Error;
209
210 if (dec->is_alpha_decoded_) { // finished?
211 ALPHDelete(dec->alph_dec_);
212 dec->alph_dec_ = NULL;
213 if (dec->alpha_dithering_ > 0) {
214 uint8_t* const alpha = dec->alpha_plane_ + io->crop_top * width
215 + io->crop_left;
216 if (!WebPDequantizeLevels(alpha,
217 io->crop_right - io->crop_left,
218 io->crop_bottom - io->crop_top,
219 width, dec->alpha_dithering_)) {
220 goto Error;
221 }
222 }
223 }
224 }
225
226 // Return a pointer to the current decoded row.
227 return dec->alpha_plane_ + row * width;
228
229 Error:
230 WebPDeallocateAlphaMemory(dec);
231 return NULL;
232}
233