qemu/ui/vnc-enc-tight.h

11  * Permission is hereby granted, free of charge, to any person obtaining a copy
15  * copies of the Software, and to permit persons to whom the Software is
21  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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):
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",
49  * If the compression type is "basic", then bits 6..4 of the
52  *   bits 5-4:  decimal representation is the index of a particular zlib
54  *   bit 6:     if 1, then a "filter id" byte is following this byte.
59  *-- If the compression type is "fill", then the only pixel value follows, in
63  *-- If the compression type is "jpeg" or "png", the following data stream
69  * Data size is compactly represented in one, two or three bytes, according
82  *-- If the compression type is "basic" and bit 6 of the compression control
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
101  * Pseudo-code for converting intensities to differences is the following:
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
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
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
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
130  * If the compression is not used, then the pixel data is sent as is,
136  * Data size is compactly represented in one, two or three bytes, just like
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
148  * the compression type is "fill", "jpeg" or "png".
151  * when bits-per-pixel value is either 16 or 32, not 8.
154  * pixels. If a rectangle is wider, it must be split into several rectangles