/* * QEMU VNC display driver: tight encoding * * From libvncserver/rfb/rfbproto.h * Copyright (C) 2005 Rohit Kumar, Johannes E. Schindelin * Copyright (C) 2000-2002 Constantin Kaplinsky. All Rights Reserved. * Copyright (C) 2000 Tridia Corporation. All Rights Reserved. * Copyright (C) 1999 AT&T Laboratories Cambridge. All Rights Reserved. * * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN * THE SOFTWARE. */ #ifndef VNC_ENCODING_TIGHT_H #define VNC_ENCODING_TIGHT_H /*- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * Tight Encoding. * *-- The first byte of each Tight-encoded rectangle is a "compression control * byte". Its format is as follows (bit 0 is the least significant one): * * bit 0: if 1, then compression stream 0 should be reset; * bit 1: if 1, then compression stream 1 should be reset; * bit 2: if 1, then compression stream 2 should be reset; * bit 3: if 1, then compression stream 3 should be reset; * bits 7-4: if 1000 (0x08), then the compression type is "fill", * if 1001 (0x09), then the compression type is "jpeg", * if 1010 (0x0A), then the compression type is "png", * if 0xxx, then the compression type is "basic", * values greater than 1010 are not valid. * * If the compression type is "basic", then bits 6..4 of the * compression control byte (those xxx in 0xxx) specify the following: * * bits 5-4: decimal representation is the index of a particular zlib * stream which should be used for decompressing the data; * bit 6: if 1, then a "filter id" byte is following this byte. * *-- The data that follows after the compression control byte described * above depends on the compression type ("fill", "jpeg", "png" or "basic"). * *-- If the compression type is "fill", then the only pixel value follows, in * client pixel format (see NOTE 1). This value applies to all pixels of the * rectangle. * *-- If the compression type is "jpeg" or "png", the following data stream * looks like this: * * 1..3 bytes: data size (N) in compact representation; * N bytes: JPEG or PNG image. * * Data size is compactly represented in one, two or three bytes, according * to the following scheme: * * 0xxxxxxx (for values 0..127) * 1xxxxxxx 0yyyyyyy (for values 128..16383) * 1xxxxxxx 1yyyyyyy zzzzzzzz (for values 16384..4194303) * * Here each character denotes one bit, xxxxxxx are the least significant 7 * bits of the value (bits 0-6), yyyyyyy are bits 7-13, and zzzzzzzz are the * most significant 8 bits (bits 14-21). For example, decimal value 10000 * should be represented as two bytes: binary 10010000 01001110, or * hexadecimal 90 4E. * *-- If the compression type is "basic" and bit 6 of the compression control * byte was set to 1, then the next (second) byte specifies "filter id" which * tells the decoder what filter type was used by the encoder to pre-process * pixel data before the compression. The "filter id" byte can be one of the * following: * * 0: no filter ("copy" filter); * 1: "palette" filter; * 2: "gradient" filter. * *-- If bit 6 of the compression control byte is set to 0 (no "filter id" * byte), or if the filter id is 0, then raw pixel values in the client * format (see NOTE 1) will be compressed. See below details on the * compression. * *-- The "gradient" filter pre-processes pixel data with a simple algorithm * which converts each color component to a difference between a "predicted" * intensity and the actual intensity. Such a technique does not affect * uncompressed data size, but helps to compress photo-like images better. * Pseudo-code for converting intensities to differences is the following: * * P[i,j] := V[i-1,j] + V[i,j-1] - V[i-1,j-1]; * if (P[i,j] < 0) then P[i,j] := 0; * if (P[i,j] > MAX) then P[i,j] := MAX; * D[i,j] := V[i,j] - P[i,j]; * * Here V[i,j] is the intensity of a color component for a pixel at * coordinates (i,j). MAX is the maximum value of intensity for a color * component. * *-- The "palette" filter converts true-color pixel data to indexed colors * and a palette which can consist of 2..256 colors. If the number of colors * is 2, then each pixel is encoded in 1 bit, otherwise 8 bits is used to * encode one pixel. 1-bit encoding is performed such way that the most * significant bits correspond to the leftmost pixels, and each raw of pixels * is aligned to the byte boundary. When "palette" filter is used, the * palette is sent before the pixel data. The palette begins with an unsigned * byte which value is the number of colors in the palette minus 1 (i.e. 1 * means 2 colors, 255 means 256 colors in the palette). Then follows the * palette itself which consist of pixel values in client pixel format (see * NOTE 1). * *-- The pixel data is compressed using the zlib library. But if the data * size after applying the filter but before the compression is less then 12, * then the data is sent as is, uncompressed. Four separate zlib streams * (0..3) can be used and the decoder should read the actual stream id from * the compression control byte (see NOTE 2). * * If the compression is not used, then the pixel data is sent as is, * otherwise the data stream looks like this: * * 1..3 bytes: data size (N) in compact representation; * N bytes: zlib-compressed data. * * Data size is compactly represented in one, two or three bytes, just like * in the "jpeg" compression method (see above). * *-- NOTE 1. If the color depth is 24, and all three color components are * 8-bit wide, then one pixel in Tight encoding is always represented by * three bytes, where the first byte is red component, the second byte is * green component, and the third byte is blue component of the pixel color * value. This applies to colors in palettes as well. * *-- NOTE 2. The decoder must reset compression streams' states before * decoding the rectangle, if some of bits 0,1,2,3 in the compression control * byte are set to 1. Note that the decoder must reset zlib streams even if * the compression type is "fill", "jpeg" or "png". * *-- NOTE 3. The "gradient" filter and "jpeg" compression may be used only * when bits-per-pixel value is either 16 or 32, not 8. * *-- NOTE 4. The width of any Tight-encoded rectangle cannot exceed 2048 * pixels. If a rectangle is wider, it must be split into several rectangles * and each one should be encoded separately. * */ #define VNC_TIGHT_EXPLICIT_FILTER 0x04 #define VNC_TIGHT_FILL 0x08 #define VNC_TIGHT_JPEG 0x09 #define VNC_TIGHT_PNG 0x0A #define VNC_TIGHT_MAX_SUBENCODING 0x0A /* Filters to improve compression efficiency */ #define VNC_TIGHT_FILTER_COPY 0x00 #define VNC_TIGHT_FILTER_PALETTE 0x01 #define VNC_TIGHT_FILTER_GRADIENT 0x02 /* Note: The following constant should not be changed. */ #define VNC_TIGHT_MIN_TO_COMPRESS 12 /* The parameters below may be adjusted. */ #define VNC_TIGHT_MIN_SPLIT_RECT_SIZE 4096 #define VNC_TIGHT_MIN_SOLID_SUBRECT_SIZE 2048 #define VNC_TIGHT_MAX_SPLIT_TILE_SIZE 16 #define VNC_TIGHT_JPEG_MIN_RECT_SIZE 4096 #define VNC_TIGHT_DETECT_SUBROW_WIDTH 7 #define VNC_TIGHT_DETECT_MIN_WIDTH 8 #define VNC_TIGHT_DETECT_MIN_HEIGHT 8 #endif /* VNC_ENCODING_TIGHT_H */