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[qemu.git] / ui / vnc-enc-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_ENC_TIGHT_H
31 #define VNC_ENC_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 1010 (0x0A), then the compression type is "png",
46 * if 0xxx, then the compression type is "basic",
47 * values greater than 1010 are not valid.
48 *
49 * If the compression type is "basic", then bits 6..4 of the
50 * compression control byte (those xxx in 0xxx) specify the following:
51 *
52 * bits 5-4: decimal representation is the index of a particular zlib
53 * stream which should be used for decompressing the data;
54 * bit 6: if 1, then a "filter id" byte is following this byte.
55 *
56 *-- The data that follows after the compression control byte described
57 * above depends on the compression type ("fill", "jpeg", "png" or "basic").
58 *
59 *-- If the compression type is "fill", then the only pixel value follows, in
60 * client pixel format (see NOTE 1). This value applies to all pixels of the
61 * rectangle.
62 *
63 *-- If the compression type is "jpeg" or "png", the following data stream
64 * looks like this:
65 *
66 * 1..3 bytes: data size (N) in compact representation;
67 * N bytes: JPEG or PNG image.
68 *
69 * Data size is compactly represented in one, two or three bytes, according
70 * to the following scheme:
71 *
72 * 0xxxxxxx (for values 0..127)
73 * 1xxxxxxx 0yyyyyyy (for values 128..16383)
74 * 1xxxxxxx 1yyyyyyy zzzzzzzz (for values 16384..4194303)
75 *
76 * Here each character denotes one bit, xxxxxxx are the least significant 7
77 * bits of the value (bits 0-6), yyyyyyy are bits 7-13, and zzzzzzzz are the
78 * most significant 8 bits (bits 14-21). For example, decimal value 10000
79 * should be represented as two bytes: binary 10010000 01001110, or
80 * hexadecimal 90 4E.
81 *
82 *-- If the compression type is "basic" and bit 6 of the compression control
83 * byte was set to 1, then the next (second) byte specifies "filter id" which
84 * tells the decoder what filter type was used by the encoder to pre-process
85 * pixel data before the compression. The "filter id" byte can be one of the
86 * following:
87 *
88 * 0: no filter ("copy" filter);
89 * 1: "palette" filter;
90 * 2: "gradient" filter.
91 *
92 *-- If bit 6 of the compression control byte is set to 0 (no "filter id"
93 * byte), or if the filter id is 0, then raw pixel values in the client
94 * format (see NOTE 1) will be compressed. See below details on the
95 * compression.
96 *
97 *-- The "gradient" filter pre-processes pixel data with a simple algorithm
98 * which converts each color component to a difference between a "predicted"
99 * intensity and the actual intensity. Such a technique does not affect
100 * uncompressed data size, but helps to compress photo-like images better.
101 * Pseudo-code for converting intensities to differences is the following:
102 *
103 * P[i,j] := V[i-1,j] + V[i,j-1] - V[i-1,j-1];
104 * if (P[i,j] < 0) then P[i,j] := 0;
105 * if (P[i,j] > MAX) then P[i,j] := MAX;
106 * D[i,j] := V[i,j] - P[i,j];
107 *
108 * Here V[i,j] is the intensity of a color component for a pixel at
109 * coordinates (i,j). MAX is the maximum value of intensity for a color
110 * component.
111 *
112 *-- The "palette" filter converts true-color pixel data to indexed colors
113 * and a palette which can consist of 2..256 colors. If the number of colors
114 * is 2, then each pixel is encoded in 1 bit, otherwise 8 bits is used to
115 * encode one pixel. 1-bit encoding is performed such way that the most
116 * significant bits correspond to the leftmost pixels, and each raw of pixels
117 * is aligned to the byte boundary. When "palette" filter is used, the
118 * palette is sent before the pixel data. The palette begins with an unsigned
119 * byte which value is the number of colors in the palette minus 1 (i.e. 1
120 * means 2 colors, 255 means 256 colors in the palette). Then follows the
121 * palette itself which consist of pixel values in client pixel format (see
122 * NOTE 1).
123 *
124 *-- The pixel data is compressed using the zlib library. But if the data
125 * size after applying the filter but before the compression is less then 12,
126 * then the data is sent as is, uncompressed. Four separate zlib streams
127 * (0..3) can be used and the decoder should read the actual stream id from
128 * the compression control byte (see NOTE 2).
129 *
130 * If the compression is not used, then the pixel data is sent as is,
131 * otherwise the data stream looks like this:
132 *
133 * 1..3 bytes: data size (N) in compact representation;
134 * N bytes: zlib-compressed data.
135 *
136 * Data size is compactly represented in one, two or three bytes, just like
137 * in the "jpeg" compression method (see above).
138 *
139 *-- NOTE 1. If the color depth is 24, and all three color components are
140 * 8-bit wide, then one pixel in Tight encoding is always represented by
141 * three bytes, where the first byte is red component, the second byte is
142 * green component, and the third byte is blue component of the pixel color
143 * value. This applies to colors in palettes as well.
144 *
145 *-- NOTE 2. The decoder must reset compression streams' states before
146 * decoding the rectangle, if some of bits 0,1,2,3 in the compression control
147 * byte are set to 1. Note that the decoder must reset zlib streams even if
148 * the compression type is "fill", "jpeg" or "png".
149 *
150 *-- NOTE 3. The "gradient" filter and "jpeg" compression may be used only
151 * when bits-per-pixel value is either 16 or 32, not 8.
152 *
153 *-- NOTE 4. The width of any Tight-encoded rectangle cannot exceed 2048
154 * pixels. If a rectangle is wider, it must be split into several rectangles
155 * and each one should be encoded separately.
156 *
157 */
158
159 #define VNC_TIGHT_EXPLICIT_FILTER 0x04
160 #define VNC_TIGHT_FILL 0x08
161 #define VNC_TIGHT_JPEG 0x09
162 #define VNC_TIGHT_PNG 0x0A
163 #define VNC_TIGHT_MAX_SUBENCODING 0x0A
164
165 /* Filters to improve compression efficiency */
166 #define VNC_TIGHT_FILTER_COPY 0x00
167 #define VNC_TIGHT_FILTER_PALETTE 0x01
168 #define VNC_TIGHT_FILTER_GRADIENT 0x02
169
170 /* Note: The following constant should not be changed. */
171 #define VNC_TIGHT_MIN_TO_COMPRESS 12
172
173 /* The parameters below may be adjusted. */
174 #define VNC_TIGHT_MIN_SPLIT_RECT_SIZE 4096
175 #define VNC_TIGHT_MIN_SOLID_SUBRECT_SIZE 2048
176 #define VNC_TIGHT_MAX_SPLIT_TILE_SIZE 16
177
178 #define VNC_TIGHT_JPEG_MIN_RECT_SIZE 4096
179 #define VNC_TIGHT_DETECT_SUBROW_WIDTH 7
180 #define VNC_TIGHT_DETECT_MIN_WIDTH 8
181 #define VNC_TIGHT_DETECT_MIN_HEIGHT 8
182
183 #endif /* VNC_ENC_TIGHT_H */