xref: /openbmc/qemu/ui/vnc-enc-tight.h (revision 1c8e93fb)
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 */
184