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 "./vp8i.h"
16#include "./vp8li.h"
17#include "../utils/filters.h"
18#include "../utils/quant_levels_dec.h"
19#include "../webp/format_constants.h"
20
21#if defined(__cplusplus) || defined(c_plusplus)
22extern "C" {
23#endif
24
25//------------------------------------------------------------------------------
26// Decodes the compressed data 'data' of size 'data_size' into the 'output'.
27// The 'output' buffer should be pre-allocated and must be of the same
28// dimension 'height'x'width', as that of the image.
29//
30// Returns 1 on successfully decoding the compressed alpha and
31//         0 if either:
32//           error in bit-stream header (invalid compression mode or filter), or
33//           error returned by appropriate compression method.
34
35static int DecodeAlpha(const uint8_t* data, size_t data_size,
36                       int width, int height, uint8_t* output) {
37  WEBP_FILTER_TYPE filter;
38  int pre_processing;
39  int rsrv;
40  int ok = 0;
41  int method;
42  const uint8_t* const alpha_data = data + ALPHA_HEADER_LEN;
43  const size_t alpha_data_size = data_size - ALPHA_HEADER_LEN;
44
45  assert(width > 0 && height > 0);
46  assert(data != NULL && output != NULL);
47
48  if (data_size <= ALPHA_HEADER_LEN) {
49    return 0;
50  }
51
52  method = (data[0] >> 0) & 0x03;
53  filter = (data[0] >> 2) & 0x03;
54  pre_processing = (data[0] >> 4) & 0x03;
55  rsrv = (data[0] >> 6) & 0x03;
56  if (method < ALPHA_NO_COMPRESSION ||
57      method > ALPHA_LOSSLESS_COMPRESSION ||
58      filter >= WEBP_FILTER_LAST ||
59      pre_processing > ALPHA_PREPROCESSED_LEVELS ||
60      rsrv != 0) {
61    return 0;
62  }
63
64  if (method == ALPHA_NO_COMPRESSION) {
65    const size_t alpha_decoded_size = height * width;
66    ok = (alpha_data_size >= alpha_decoded_size);
67    if (ok) memcpy(output, alpha_data, alpha_decoded_size);
68  } else {
69    ok = VP8LDecodeAlphaImageStream(width, height, alpha_data, alpha_data_size,
70                                    output);
71  }
72
73  if (ok) {
74    WebPUnfilterFunc unfilter_func = WebPUnfilters[filter];
75    if (unfilter_func != NULL) {
76      // TODO(vikas): Implement on-the-fly decoding & filter mechanism to decode
77      // and apply filter per image-row.
78      unfilter_func(width, height, width, output);
79    }
80    if (pre_processing == ALPHA_PREPROCESSED_LEVELS) {
81      ok = DequantizeLevels(output, width, height);
82    }
83  }
84
85  return ok;
86}
87
88//------------------------------------------------------------------------------
89
90const uint8_t* VP8DecompressAlphaRows(VP8Decoder* const dec,
91                                      int row, int num_rows) {
92  const int width = dec->pic_hdr_.width_;
93  const int height = dec->pic_hdr_.height_;
94
95  if (row < 0 || num_rows < 0 || row + num_rows > height) {
96    return NULL;    // sanity check.
97  }
98
99  if (row == 0) {
100    // Decode everything during the first call.
101    assert(!dec->is_alpha_decoded_);
102    if (!DecodeAlpha(dec->alpha_data_, (size_t)dec->alpha_data_size_,
103                     width, height, dec->alpha_plane_)) {
104      return NULL;  // Error.
105    }
106    dec->is_alpha_decoded_ = 1;
107  }
108
109  // Return a pointer to the current decoded row.
110  return dec->alpha_plane_ + row * width;
111}
112
113#if defined(__cplusplus) || defined(c_plusplus)
114}    // extern "C"
115#endif
116