third_party/libwebp/dec/alpha.c

   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 "./alphai.h"
  16 #include "./vp8i.h"
  17 #include "./vp8li.h"
  18 #include "../utils/quant_levels_dec.h"
  19 #include "../utils/utils.h"
  20 #include "../webp/format_constants.h"
  21
  22 //------------------------------------------------------------------------------
  23 // ALPHDecoder object.
  24
  25 ALPHDecoder* ALPHNew(void) {
  26   ALPHDecoder* const dec = (ALPHDecoder*)WebPSafeCalloc(1ULL, sizeof(*dec));
  27   return dec;
  28 }
  29
  30 void ALPHDelete(ALPHDecoder* const dec) {
  31   if (dec != NULL) {
  32     VP8LDelete(dec->vp8l_dec_);
  33     dec->vp8l_dec_ = NULL;
  34     WebPSafeFree(dec);
  35   }
  36 }
  37
  38 //------------------------------------------------------------------------------
  39 // Decoding.
  40
  41 // Initialize alpha decoding by parsing the alpha header and decoding the image
  42 // header for alpha data stored using lossless compression.
  43 // Returns false in case of error in alpha header (data too short, invalid
  44 // compression method or filter, error in lossless header data etc).
  45 static int ALPHInit(ALPHDecoder* const dec, const uint8_t* data,
  46                     size_t data_size, int width, int height, uint8_t* output) {
  47   int ok = 0;
  48   const uint8_t* const alpha_data = data + ALPHA_HEADER_LEN;
  49   const size_t alpha_data_size = data_size - ALPHA_HEADER_LEN;
  50   int rsrv;
  51
  52   assert(width > 0 && height > 0);
  53   assert(data != NULL && output != NULL);
  54
  55   dec->width_ = width;
  56   dec->height_ = height;
  57
  58   if (data_size <= ALPHA_HEADER_LEN) {
  59     return 0;
  60   }
  61
  62   dec->method_ = (data[0] >> 0) & 0x03;
  63   dec->filter_ = (data[0] >> 2) & 0x03;
  64   dec->pre_processing_ = (data[0] >> 4) & 0x03;
  65   rsrv = (data[0] >> 6) & 0x03;
  66   if (dec->method_ < ALPHA_NO_COMPRESSION ||
  67       dec->method_ > ALPHA_LOSSLESS_COMPRESSION ||
  68       dec->filter_ >= WEBP_FILTER_LAST ||
  69       dec->pre_processing_ > ALPHA_PREPROCESSED_LEVELS ||
  70       rsrv != 0) {
  71     return 0;
  72   }
  73
  74   if (dec->method_ == ALPHA_NO_COMPRESSION) {
  75     const size_t alpha_decoded_size = dec->width_ * dec->height_;
  76     ok = (alpha_data_size >= alpha_decoded_size);
  77   } else {
  78     assert(dec->method_ == ALPHA_LOSSLESS_COMPRESSION);
  79     ok = VP8LDecodeAlphaHeader(dec, alpha_data, alpha_data_size, output);
  80   }
  81   return ok;
  82 }
  83
  84 // Decodes, unfilters and dequantizes *at least* 'num_rows' rows of alpha
  85 // starting from row number 'row'. It assumes that rows up to (row - 1) have
  86 // already been decoded.
  87 // Returns false in case of bitstream error.
  88 static int ALPHDecode(VP8Decoder* const dec, int row, int num_rows) {
  89   ALPHDecoder* const alph_dec = dec->alph_dec_;
  90   const int width = alph_dec->width_;
  91   const int height = alph_dec->height_;
  92   WebPUnfilterFunc unfilter_func = WebPUnfilters[alph_dec->filter_];
  93   uint8_t* const output = dec->alpha_plane_;
  94   if (alph_dec->method_ == ALPHA_NO_COMPRESSION) {
  95     const size_t offset = row * width;
  96     const size_t num_pixels = num_rows * width;
  97     assert(dec->alpha_data_size_ >= ALPHA_HEADER_LEN + offset + num_pixels);
  98     memcpy(dec->alpha_plane_ + offset,
  99            dec->alpha_data_ + ALPHA_HEADER_LEN + offset, num_pixels);
 100   } else {  // alph_dec->method_ == ALPHA_LOSSLESS_COMPRESSION
 101     assert(alph_dec->vp8l_dec_ != NULL);
 102     if (!VP8LDecodeAlphaImageStream(alph_dec, row + num_rows)) {
 103       return 0;
 104     }
 105   }
 106
 107   if (unfilter_func != NULL) {
 108     unfilter_func(width, height, width, row, num_rows, output);
 109   }
 110
 111   if (row + num_rows == dec->pic_hdr_.height_) {
 112     dec->is_alpha_decoded_ = 1;
 113   }
 114   return 1;
 115 }
 116
 117 //------------------------------------------------------------------------------
 118 // Main entry point.
 119
 120 const uint8_t* VP8DecompressAlphaRows(VP8Decoder* const dec,
 121                                       int row, int num_rows) {
 122   const int width = dec->pic_hdr_.width_;
 123   const int height = dec->pic_hdr_.height_;
 124
 125   if (row < 0 || num_rows <= 0 || row + num_rows > height) {
 126     return NULL;    // sanity check.
 127   }
 128
 129   if (row == 0) {
 130     // Initialize decoding.
 131     assert(dec->alpha_plane_ != NULL);
 132     dec->alph_dec_ = ALPHNew();
 133     if (dec->alph_dec_ == NULL) return NULL;
 134     if (!ALPHInit(dec->alph_dec_, dec->alpha_data_, dec->alpha_data_size_,
 135                   width, height, dec->alpha_plane_)) {
 136       ALPHDelete(dec->alph_dec_);
 137       dec->alph_dec_ = NULL;
 138       return NULL;
 139     }
 140     // if we allowed use of alpha dithering, check whether it's needed at all
 141     if (dec->alph_dec_->pre_processing_ != ALPHA_PREPROCESSED_LEVELS) {
 142       dec->alpha_dithering_ = 0;  // disable dithering
 143     } else {
 144       num_rows = height;          // decode everything in one pass
 145     }
 146   }
 147
 148   if (!dec->is_alpha_decoded_) {
 149     int ok = 0;
 150     assert(dec->alph_dec_ != NULL);
 151     ok = ALPHDecode(dec, row, num_rows);
 152     if (ok && dec->alpha_dithering_ > 0) {
 153       ok = WebPDequantizeLevels(dec->alpha_plane_, width, height,
 154                                 dec->alpha_dithering_);
 155     }
 156     if (!ok || dec->is_alpha_decoded_) {
 157       ALPHDelete(dec->alph_dec_);
 158       dec->alph_dec_ = NULL;
 159     }
 160     if (!ok) return NULL;  // Error.
 161   }
 162
 163   // Return a pointer to the current decoded row.
 164   return dec->alpha_plane_ + row * width;
 165 }