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Guide to writing image loaders for xli

Include files

      #include "xli.h"

Identify function

int xyyzIdent(fullname, name)
     char *fullname, *name;
{
}

where this is an xyyz type image loader file.

fullname is the name including path, while name is the short
name of the file that is used as a title, or to refer to the file
in messages.

Return 0 if the image is NOT identified.

Return 1 if the image IS identified.

If the file is identified, use a message something like:


printf("%s is a %dx%d xyyz image with %d colors\n",
         name, width, height, ncolors);

Try and be quick about identifying the image - don't read the whole image
just to identify it !

Use printf even if something is wrong with the file.
Use perror for a system error - ie. unable to open file.

Loading the image

Image xyyzLoad(fullname, image_ops, verbose)
     ImageOptions *image_ops;
     char         *fullname;
     boolean       verbose;
{
}

Identify the image as quickly as possible.

Return NULL if the image is not identified.

Otherwise Return a pointer to an image structure with the image in it.

If the image is properly identified, but there is something wrong with it
before anything useful is read in, report the error  - ie.


fprintf(stderr,"xyyzLoad: %s - corrupted color map\n",name);

clean up (ie. release the image structure and any allocated memory) and
return NULL.

If the image is properly identified, and there is something wrong with it,
but something useful has been read in (ie. color maps etc. have been
loaded, and part of the image is loaded), report the error using
fprintf (as above) and return what there is of the image.

Remember to release and temporary memory allocated on returning, whether
the image is loaded ok, or if something goes wrong.

Remember to read any trailing options before returning a successfully loaded
image, and before closing the file.
Trailing options are read by calling the function:


read_trail_opt(image_ops, zf, image, verbose)
    ImageOptions *image_ops;
    ZFILE        *zf;
    Image        *image;
    boolean       verbose;

Remember to close the file before returning.

Remember to add any additional info to the image structure -
ie. name, gamma if known etc.

NEVER EVER exit(). There may be other image loaders and other images to load.

Use printf to give verbose output on image details.

Use fprintf(stderr," ... ");  to give error warning if the file is corrupted.

use perror for a system error - ie. unable to open file.

Useful info in image_ops:

        char         *name;         /* Short name of image */

Useful things to set in the image structure:

        char         *title;  /* name of image */
        RGBMap        rgb;    / RGB map of image if IRGB type */
        byte         *data;   /* data, rounded to full byte for each row */
        float             gamma;        /* gamma of display the image is adjusted */
                                        /* for, if know. */

Creating and destroying Image structures:

/* For a monochrome bitmap */
Image *newBitImage(width, height)
     unsigned int width, height;

/* For a color image with a color map */
Image *newRGBImage(width, height, depth)
     unsigned int width, height, depth;

/* For a true color image */
Image *newTrueImage(width, height)
     unsigned int width, height;

And the image can be freed with:


void freeImageData(image)
     Image *image;

Examine another image loader (ie. gif.c) to see how to set up a color map.

File input resources:

/*
  Open a file by name and return a pointer to
  a file descriptor.
 */
ZFILE *zopen(name)
     char *name;

/*
  Read some data into a buffer
 */
int zread(zf, buf, len)
     ZFILE *zf;
     byte *buf;
     int len;

/*
  Macro that returns a character from the file.
 */
zgetc(zf)
     ZFILE *zf;

/*
  Function that reads a string into a buffer
 */
char *zgets(buf, size, zf)
     char         *buf;
     unsigned int  size;
     ZFILE        *zf;

/* Return the files EOF status */
int zeof(zf)
     ZFILE *zf;

/*
  Clear any errors (ie. EOF)
 */
void zclearerr(zf)
     ZFILE *zf;

/*
  Turn off caching when an image has been identified
  and there is no need to re-open it. The cached part
  of the file is still kept, but any reads past this
  point are not cached.
 */
void znocache(zf)
     ZFILE *zf;

/*
  Rewind the cached file. This won't work if the file
  is stdin and we have read past the cached part of
  the file. Return TRUE on success.
 */
boolean zrewind(zf)
     ZFILE *zf;

/*
  Return a block of data back to the input stream.
  Useful for a load routine that does its own buffering
  and wants to return what is left after it has read
  an image. (This is needed to allow trailing options
  to be recognized.) Can also be used instead of ungetc().
 */
void zunread(zf, buf, len)
     ZFILE *zf;
     byte *buf;
     int len;

/*
  Close a file.
  The file is not actually closed until zreset is called,
  in case another loader wants to re-open it.
 */
void zclose(zf)
     ZFILE *zf;

/*
  Really close a file. Not used by imageLoad functions.
 */
void zreset(filename)
     char *filename;

Some macros are provided to facilitate reading and writing elements larger
than a character from/to a data buffer according to the desired endianness:

Big endian:


#define memToVal(PTR,LEN)

#define valToMem(VAL,PTR,LEN)

Little Endian


#define memToValLSB(PTR,LEN)

#define valToMemLSB(VAL,PTR,LEN)

Memory allocation:

/* Duplicate a string. Good for making up the image title etc. */
char *dupString(s)
     char *s;

byte *lmalloc(size)
     unsigned int size;

byte *lcalloc(size)
     unsigned int size;

void lfree(area)
     byte *area;

Be careful not to call lfree with NULL. It may cause a fault.

Other facilities:

/* Copy a block of memory */
bcopy(S,D,N)

/* Zero a block of memory */
bzero(P,N)

/* Fill a block of memory with a value */
bfill(P,N,C)

If all else fails:

Index

Guide to writing image loaders for xli

Include files

Identify function

Loading the image

Useful info in image_ops:

Useful things to set in the image structure:

Creating and destroying Image structures:

File input resources:

Memory allocation:

Other facilities:

If all else fails:

Партнёры:

Хостинг: