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KDE Image I/O library
---------------------
This library allows applications that use the Qt library
(i.e. QImageIO, QImage, QPixmap and friends) to read and
write images in extra formats. Current formats include:
JPEG <read> <write>
JPEG2000 <read> <write>
XV <read> <write>
EPS <read> <write>
NETPBM <incomplete>
PNG <read> <write, only with newer libraries>
TIFF <read>
TGA <read> <write>
PCX <read> <write>
SGI <read> <write> (images/x-rgb: *.bw, *.rgb, *.rgba, *.sgi)
DDS <read>
XCF <read>
(Some example files are in kdenonbeta/kimgio_examples.)
To use these formats, you only need to:
1. link the application with the libkio library
2. Include the <kimageio.h> header
3. call KImageIO::registerFormats() once, somewhere in your code
before you load an image.
Writing handlers
----------------
0. Please read the documentation for the QImageIO class in the Qt
documentation.
1. When writing handlers, there is a function naming convention;
suppose, for example, we were writing PNG read and write handlers,
we would name them
void kimgio_png_read ( QImageIO * );
void kimgio_png_write( QImageIO * );
ie
kimgio_<format>_<read/write>
This should reduce the chance of identifier clashes with other code.
2. Remember that a given KDE application may try to load dozens of
images at once such as when loading icons, or creating thumbnails.
Also, it may well be loading them over a network connection.
Therefore,
- Avoid creating temporary files or allocating too much memory
when decoding and encoding. Especially try to avoid firing off
external programs.
- Don't assume that the IODevice which is the source or target
of the image data is pointing to a file on the local filesystem.
Use the IODevice methods to read and write image data.
- Check for file corruption or premature end of the image,
especially before using values read from the file
e.g. for memory allocations.
3. If you only have either a reader or the writer for a particular
format, don't use NULL in QImageIO::defineIOHandler. Instead, write
a stub function for the unimplemented handler which displays a message
on standard output. This prevents kimgio-using programs dumping core
when attempting to call the unimplemented handler.
Yours in good faith and pedantry,
Sirtaj Singh Kang <[email protected]>, 23 September 1998.
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