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 | |