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 (at) 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) 22 extern "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 35 static 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 90 const 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