vnc-encoding-tight.h

   1 /*
   2  * QEMU VNC display driver: tight encoding
   3  *
   4  * From libvncserver/rfb/rfbproto.h
   5  * Copyright (C) 2005 Rohit Kumar, Johannes E. Schindelin
   6  * Copyright (C) 2000-2002 Constantin Kaplinsky.  All Rights Reserved.
   7  * Copyright (C) 2000 Tridia Corporation.  All Rights Reserved.
   8  * Copyright (C) 1999 AT&T Laboratories Cambridge.  All Rights Reserved.
   9  *
  10  *
  11  * Permission is hereby granted, free of charge, to any person obtaining a copy
  12  * of this software and associated documentation files (the "Software"), to deal
  13  * in the Software without restriction, including without limitation the rights
  14  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  15  * copies of the Software, and to permit persons to whom the Software is
  16  * furnished to do so, subject to the following conditions:
  17  *
  18  * The above copyright notice and this permission notice shall be included in
  19  * all copies or substantial portions of the Software.
  20  *
  21  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  22  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  23  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  24  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  25  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  26  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  27  * THE SOFTWARE.
  28  */
  29
  30 #ifndef VNC_ENCODING_TIGHT_H
  31 #define VNC_ENCODING_TIGHT_H
  32
  33 /*- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  34  * Tight Encoding.
  35  *
  36  *-- The first byte of each Tight-encoded rectangle is a "compression control
  37  *   byte". Its format is as follows (bit 0 is the least significant one):
  38  *
  39  *   bit 0:    if 1, then compression stream 0 should be reset;
  40  *   bit 1:    if 1, then compression stream 1 should be reset;
  41  *   bit 2:    if 1, then compression stream 2 should be reset;
  42  *   bit 3:    if 1, then compression stream 3 should be reset;
  43  *   bits 7-4: if 1000 (0x08), then the compression type is "fill",
  44  *             if 1001 (0x09), then the compression type is "jpeg",
  45  *             if 0xxx, then the compression type is "basic",
  46  *             values greater than 1001 are not valid.
  47  *
  48  * If the compression type is "basic", then bits 6..4 of the
  49  * compression control byte (those xxx in 0xxx) specify the following:
  50  *
  51  *   bits 5-4:  decimal representation is the index of a particular zlib
  52  *              stream which should be used for decompressing the data;
  53  *   bit 6:     if 1, then a "filter id" byte is following this byte.
  54  *
  55  *-- The data that follows after the compression control byte described
  56  * above depends on the compression type ("fill", "jpeg" or "basic").
  57  *
  58  *-- If the compression type is "fill", then the only pixel value follows, in
  59  * client pixel format (see NOTE 1). This value applies to all pixels of the
  60  * rectangle.
  61  *
  62  *-- If the compression type is "jpeg", the following data stream looks like
  63  * this:
  64  *
  65  *   1..3 bytes:  data size (N) in compact representation;
  66  *   N bytes:     JPEG image.
  67  *
  68  * Data size is compactly represented in one, two or three bytes, according
  69  * to the following scheme:
  70  *
  71  *  0xxxxxxx                    (for values 0..127)
  72  *  1xxxxxxx 0yyyyyyy           (for values 128..16383)
  73  *  1xxxxxxx 1yyyyyyy zzzzzzzz  (for values 16384..4194303)
  74  *
  75  * Here each character denotes one bit, xxxxxxx are the least significant 7
  76  * bits of the value (bits 0-6), yyyyyyy are bits 7-13, and zzzzzzzz are the
  77  * most significant 8 bits (bits 14-21). For example, decimal value 10000
  78  * should be represented as two bytes: binary 10010000 01001110, or
  79  * hexadecimal 90 4E.
  80  *
  81  *-- If the compression type is "basic" and bit 6 of the compression control
  82  * byte was set to 1, then the next (second) byte specifies "filter id" which
  83  * tells the decoder what filter type was used by the encoder to pre-process
  84  * pixel data before the compression. The "filter id" byte can be one of the
  85  * following:
  86  *
  87  *   0:  no filter ("copy" filter);
  88  *   1:  "palette" filter;
  89  *   2:  "gradient" filter.
  90  *
  91  *-- If bit 6 of the compression control byte is set to 0 (no "filter id"
  92  * byte), or if the filter id is 0, then raw pixel values in the client
  93  * format (see NOTE 1) will be compressed. See below details on the
  94  * compression.
  95  *
  96  *-- The "gradient" filter pre-processes pixel data with a simple algorithm
  97  * which converts each color component to a difference between a "predicted"
  98  * intensity and the actual intensity. Such a technique does not affect
  99  * uncompressed data size, but helps to compress photo-like images better.
 100  * Pseudo-code for converting intensities to differences is the following:
 101  *
 102  *   P[i,j] := V[i-1,j] + V[i,j-1] - V[i-1,j-1];
 103  *   if (P[i,j] < 0) then P[i,j] := 0;
 104  *   if (P[i,j] > MAX) then P[i,j] := MAX;
 105  *   D[i,j] := V[i,j] - P[i,j];
 106  *
 107  * Here V[i,j] is the intensity of a color component for a pixel at
 108  * coordinates (i,j). MAX is the maximum value of intensity for a color
 109  * component.
 110  *
 111  *-- The "palette" filter converts true-color pixel data to indexed colors
 112  * and a palette which can consist of 2..256 colors. If the number of colors
 113  * is 2, then each pixel is encoded in 1 bit, otherwise 8 bits is used to
 114  * encode one pixel. 1-bit encoding is performed such way that the most
 115  * significant bits correspond to the leftmost pixels, and each raw of pixels
 116  * is aligned to the byte boundary. When "palette" filter is used, the
 117  * palette is sent before the pixel data. The palette begins with an unsigned
 118  * byte which value is the number of colors in the palette minus 1 (i.e. 1
 119  * means 2 colors, 255 means 256 colors in the palette). Then follows the
 120  * palette itself which consist of pixel values in client pixel format (see
 121  * NOTE 1).
 122  *
 123  *-- The pixel data is compressed using the zlib library. But if the data
 124  * size after applying the filter but before the compression is less then 12,
 125  * then the data is sent as is, uncompressed. Four separate zlib streams
 126  * (0..3) can be used and the decoder should read the actual stream id from
 127  * the compression control byte (see NOTE 2).
 128  *
 129  * If the compression is not used, then the pixel data is sent as is,
 130  * otherwise the data stream looks like this:
 131  *
 132  *   1..3 bytes:  data size (N) in compact representation;
 133  *   N bytes:     zlib-compressed data.
 134  *
 135  * Data size is compactly represented in one, two or three bytes, just like
 136  * in the "jpeg" compression method (see above).
 137  *
 138  *-- NOTE 1. If the color depth is 24, and all three color components are
 139  * 8-bit wide, then one pixel in Tight encoding is always represented by
 140  * three bytes, where the first byte is red component, the second byte is
 141  * green component, and the third byte is blue component of the pixel color
 142  * value. This applies to colors in palettes as well.
 143  *
 144  *-- NOTE 2. The decoder must reset compression streams' states before
 145  * decoding the rectangle, if some of bits 0,1,2,3 in the compression control
 146  * byte are set to 1. Note that the decoder must reset zlib streams even if
 147  * the compression type is "fill" or "jpeg".
 148  *
 149  *-- NOTE 3. The "gradient" filter and "jpeg" compression may be used only
 150  * when bits-per-pixel value is either 16 or 32, not 8.
 151  *
 152  *-- NOTE 4. The width of any Tight-encoded rectangle cannot exceed 2048
 153  * pixels. If a rectangle is wider, it must be split into several rectangles
 154  * and each one should be encoded separately.
 155  *
 156  */
 157
 158 #define VNC_TIGHT_EXPLICIT_FILTER       0x04
 159 #define VNC_TIGHT_FILL                  0x08
 160 #define VNC_TIGHT_JPEG                  0x09
 161 #define VNC_TIGHT_MAX_SUBENCODING       0x09
 162
 163 /* Filters to improve compression efficiency */
 164 #define VNC_TIGHT_FILTER_COPY             0x00
 165 #define VNC_TIGHT_FILTER_PALETTE          0x01
 166 #define VNC_TIGHT_FILTER_GRADIENT         0x02
 167
 168 /* Note: The following constant should not be changed. */
 169 #define VNC_TIGHT_MIN_TO_COMPRESS 12
 170
 171 /* The parameters below may be adjusted. */
 172 #define VNC_TIGHT_MIN_SPLIT_RECT_SIZE     4096
 173 #define VNC_TIGHT_MIN_SOLID_SUBRECT_SIZE  2048
 174 #define VNC_TIGHT_MAX_SPLIT_TILE_SIZE       16
 175
 176 #endif /* VNC_ENCODING_TIGHT_H */