ffmpeg/libavcodec/xface.h

   1 /*
   2  * Copyright (c) 1990 James Ashton - Sydney University
   3  * Copyright (c) 2012 Stefano Sabatini
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * FFmpeg is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with FFmpeg; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 /**
  23  * @file
  24  * X-Face common definitions.
  25  */
  26
  27 #include <stdint.h>
  28
  29 /* define the face size - 48x48x1 */
  30 #define XFACE_WIDTH  48
  31 #define XFACE_HEIGHT 48
  32 #define XFACE_PIXELS (XFACE_WIDTH * XFACE_HEIGHT)
  33
  34 /* compressed output uses the full range of printable characters.
  35  * In ASCII these are in a contiguous block so we just need to know
  36  * the first and last. The total number of printables is needed too. */
  37 #define XFACE_FIRST_PRINT '!'
  38 #define XFACE_LAST_PRINT '~'
  39 #define XFACE_PRINTS (XFACE_LAST_PRINT - XFACE_FIRST_PRINT + 1)
  40
  41 /*
  42  * Image is encoded as a big integer, using characters from '~' to
  43  * '!', for a total of 94 symbols. In order to express
  44  * 48x48*2=8*XFACE_MAX_WORDS=4608
  45  * bits, we need a total of 704 digits, as given by:
  46  * ceil(lg_94(2^4608)) = 704
  47  */
  48 #define XFACE_MAX_DIGITS 704
  49
  50 #define XFACE_BITSPERWORD 8
  51 #define XFACE_WORDCARRY (1 << XFACE_BITSPERWORD)
  52 #define XFACE_WORDMASK (XFACE_WORDCARRY - 1)
  53
  54 #define XFACE_MAX_WORDS ((XFACE_PIXELS * 2 + XFACE_BITSPERWORD - 1) / XFACE_BITSPERWORD)
  55
  56 /* Portable, very large unsigned integer arithmetic is needed.
  57  * Implementation uses arrays of WORDs. */
  58 typedef struct {
  59     int nb_words;
  60     uint8_t words[XFACE_MAX_WORDS];
  61 } BigInt;
  62
  63 /**
  64  * Add a to b storing the result in b.
  65  */
  66 void ff_big_add(BigInt *b, uint8_t a);
  67
  68 /**
  69  * Divide b by a storing the result in b and the remainder in the word
  70  * pointed to by r.
  71  */
  72 void ff_big_div(BigInt *b, uint8_t a, uint8_t *r);
  73
  74 /**
  75  * Multiply a by b storing the result in b.
  76  */
  77 void ff_big_mul(BigInt *b, uint8_t a);
  78
  79 /* Each face is encoded using 9 octrees of 16x16 each. Each level of the
  80  * trees has varying probabilities of being white, grey or black.
  81  * The table below is based on sampling many faces */
  82 enum XFaceColor { XFACE_COLOR_BLACK = 0, XFACE_COLOR_GREY, XFACE_COLOR_WHITE };
  83
  84 /* Data of varying probabilities are encoded by a value in the range 0 - 255.
  85  * The probability of the data determines the range of possible encodings.
  86  * Offset gives the first possible encoding of the range. */
  87 typedef struct {
  88     uint8_t range;
  89     uint8_t offset;
  90 } ProbRange;
  91
  92 extern const ProbRange ff_xface_probranges_per_level[4][3];
  93
  94 extern const ProbRange ff_xface_probranges_2x2[16];
  95
  96 void ff_xface_generate_face(uint8_t *dst, uint8_t * const src);