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A rasterfile is composed of three parts: first, a header containing 8 integers; second, a (possibly empty) set of colormap values; and third, the pixel image, stored a line at a time, in increasing y order. The image is layed out in the file as in a memory pixrect. Each line of the image is rounded up to the nearest 16 bits.
The header is defined by the following structure:
struct rasterfile {
int ras_magic;
int ras_width;
int ras_height;
int ras_depth;
int ras_length;
int ras_type;
int ras_maptype;
int ras_maplength;
};
The ras_magic field always contains the following constant:
#define RAS_MAGIC 0x59a66a95
The ras_width, ras_height, and ras_depth fields contain the image's width and height in pixels, and its depth in bits per pixel, respectively. The depth is either 1 or 8, corresponding to standard frame buffer depths. The ras_length field contains the length in bytes of the image data. For an unencoded image, this number is computable from the ras_width, ras_height, and ras_depth fields, but for an encoded image it must be explicitly stored in order to be available without decoding the image itself. Note: the length of the header and of the (possibly empty) colormap values are not included in the value of the ras_length field; it is only the image data length. For historical reasons, files of type RT_OLD will usually have a 0 in the ras_length field, and software expecting to encounter such files should be prepared to compute the actual image data length if needed. The ras_maptype and ras_maplength fields contain the type and length in bytes of the colormap values, respectively. If ras_maptype is not RMT_NONE and the ras_maplength is not 0, then the colormap values are the ras_maplength bytes immediately after the header. These values are either uninterpreted bytes (usually with the ras_maptype set to RMT_RAW) or the equal length red, green and blue vectors, in that order (when the ras_maptype is RMT_EQUAL_RGB). In the latter case, the ras_maplength must be three times the size in bytes of any one of the vectors.
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Created by unroff & hp-tools. © somebody (See intro for details). All Rights Reserved. Last modified 11/5/97