RLE_HDR(3) 3 (2/2/87) RLE_HDR(3)
NAME
rle_hdr - Structure for communication with RLE functions.
SYNOPSIS
#include <rle.h>
rle_hdr rle_dflt_hdr;
RLE_SET_BIT(the_hdr,bit)
RLE_CLR_BIT(the_hdr,bit)
RLE_BIT(the_hdr,bit)
rle_hdr the_hdr;
DESCRIPTION
This data structure provides communication to and between
all the RLE(5) file routines. It describes the parameters
of the image being saved or read, and contains some
variables describing file state that are private to the
routines. The public components are described below.
typedef unsigned char rle_pixel;
typedef unsigned short rle_map;
rle_hdr {
int ncolors, /* Number of colors being saved */
*bg_color,/* Background color array */
alpha, /* if / 0, save alpha channel (color -1) */
/* alpha channel background is always 0 */
background,/* if = 0, no background processing */
/* if = 1 or 2, save only non-bg pixels */
/* If 2, set clear-to-bg flag in file */
xmin, /* Min X bound of saved raster */
xmax, /* Max X bound */
ymin, /* Min Y bound */
ymax, /* Max Y bound */
ncmap, /* number of color channels in color map */
/* if = 0, color map is not saved */
cmaplen; /* Log2 of the number of entries in */
/* each channel of the color map */
rle_map *cmap; /* pointer to color map, stored as 16-bit */
/* words, with values left justified */
char **comments;/* Pointer to array of pointers */
/* to comment strings. */
FILE * rle_file; /* I/O to this file */
/*
* Bit map of channels to read/save. Indexed by (channel mod 256).
*/
char bits[256/8];
};
A global variable, rle_dflt_hdr, is available, conveniently
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RLE_HDR(3) 3 (2/2/87) RLE_HDR(3)
initialized with default values.
FIELDS
ncolors
The number of colors (exclusive of the alpha channel)
in the image. This is one greater than the largest
channel index (i.e., ncolors would be 3 if channels 0,
1, and 2 were saved, or if only channel 2 were saved.)
bg_color
A pointer to an array of ncolors integers, defines the
background color (if used). The background alpha value
is always 0, so is not included in the bg_color array.
alpha
If non-zero, an alpha channel is present as channel -1.
This should always be 0 or 1. Rle_get_setup and
rle_put_setup enforce this constraint. The alpha
channel will only be actually read or written if the
corresponding bit in bits is also set.
background
Controls whether background color processing is done.
If 0, no background processing is done at all (and
bg_color is ignored). If 1 or 2, then runs of 3 or
more pixels in the background color are not saved at
all. If 2, then these runs will be restored by
rle_getrow; if 1, they will not (this can lead to some
strange images).
xmin, xmax, ymin, ymax
The bounds of the image. All pixels from xmin to xmax,
inclusive, in rows numbered from ymin to ymax,
inclusive, will be saved. Thus the dimensions of the
image are
(xmax - xmin + 1) x (ymax - ymin + 1)
ncmap, cmaplen
The size of the saved colormap (if any). The color map
will have ncmap channels, each 2^cmaplen long. If
ncmap is zero, no color map is present.
cmap A pointer to colormap data, if present. The data is
stored in "channel major" order, so that all the values
for channel 0 precede all the values for channel 1,
etc. Each individual value is left-justified in 16
bits (i.e., the range of values is 0-65535).
comments
A pointer to picture comment data, if present. Use the
functions rle_putcom(3), rle_getcom(3), and
rle_delcom(3) to manipulate this field.
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RLE_HDR(3) 3 (2/2/87) RLE_HDR(3)
rle_file
The standard I/O FILE pointer for the file containing
this image.
bits A bitmap that selects the channels that are actually
written to/read from the file. The macros below are
used to modify this bitmap.
MACROS
The macro RLE_BIT will retrieve the state of one of the bits
in the bits map. RLE_SET_BIT, and RLE_CLR_BIT set and clear
bits in the bits map. The predefined symbols RLE_RED,
RLE_GREEN, RLE_BLUE, and RLE_ALPHA, or an integer value from
-1 to 254 may be used in these macros.
SEE ALSO
librle(3), RLE(5).
AUTHOR
Spencer W. Thomas, Todd Fuqua
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