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more tweaks, docs updated

This commit is contained in:
John Cupitt 2008-11-28 21:26:23 +00:00
parent a9bc149f58
commit a5517d3bdc
10 changed files with 117 additions and 104 deletions
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2
ChangeLog
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@ -15,6 +15,8 @@
- added affinei_all
- don't set im_error() on failed callback
- moved im_format_t to VipsFormat, now sits over VipsObject
- IM_FORMAT_FLAG_PARTIAL -> VIPS_FORMAT_PARTIAL
- updated docs
11/9/08 started 7.16.3
- oop typo in manpage for im_project()

7
TODO
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@ -6,13 +6,6 @@
user G_DEFINE_ABSTRACT_TYPE for VipsObject
- we have
VipsFormatFlags
VIPS_FORMAT_FLAG_PARTIAL
is this right? should we use singular or plural?

89
doc/src/format.tex
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@ -1,11 +1,11 @@
\section{Image formats}
\label{sec:format}
VIPS has a simple system for adding support for new image file formats. You
can register a new format and it will automatically be supported by all
the VIPS interfaces. You can ask VIPS to find a format to load a file with,
VIPS has a simple system for adding support for new image file formats.
You can ask VIPS to find a format to load a file with,
or to select a image file writer based on a filename. Convenience functions
copy a file to an \verb+IMAGE+, or an \verb+IMAGE+ to a file.
copy a file to an \verb+IMAGE+, or an \verb+IMAGE+ to a file. New formats may
be added to VIPS by simply defining a new subclass of \verb+VipsFormat+.
This is a parallel API to \verb+im_open()+, see \pref{sec:open}. The
format system is useful for images which are large or slow to open,
@ -18,7 +18,7 @@ images if you use \verb+im_open()+.
\subsection{How a format is represented}
See the man page for \verb+im_format+ for full details, but briefly, an image
See the man page for \verb+VipsFormat+ for full details, but briefly, an image
format consists of the following items:
\begin{itemize}
@ -33,7 +33,7 @@ height and does not read any pixel data) and a function which loads the pixel
data
\item
A function which will write an IMAGE to a file in the format
A function which will write an \verb+IMAGE+ to a file in the format
\item
And finally a function which examines a file in the format and returns flags
@ -44,20 +44,11 @@ version is one indicating that the file can be opened lazily
\subsection{The format table}
VIPS keeps a table of known formats, sorted by insert order and priority. You
register new formats with \verb+im_format_register()+ and, optionally,
unregister with \verb+im_format_unregister()+. You can call these operations
from a plugin's init function.
Any of the functions may be left NULL and VIPS will try to make do with what
you do supply. Of course a format with all functions as NULL will not be very
useful.
The priority system is useful if a file can be read by several possible format
loaders. For example, the libMagick loader can read TIFF files, but not as
well as VIPS' native TIFF reader. To make sure the VIPS TIFF reader is tried
first, the libMagick format is given a low priority. Most of the time, you
won't need this.
The interface to the format system is defined by the abstract base class
\verb+VipsFormat+. Formats subclass this and implement some or all of the
methods. Any of the functions may be left NULL and VIPS will try to make do
with what you do supply. Of course a format with all functions as NULL will
not be very useful.
A switch to the \verb+vips+ command-line program is handy for listing the
supported formats. Try:
@ -86,21 +77,40 @@ is_myformat( const char *filename )
return( 0 );
}
// This format adds no new members.
typedef VipsFormat VipsFormatMyformat;
typedef VipsFormatClass VipsFormatMyformatClass;
static void
vips_format_myformat_class_init( VipsFormatVipsClass *class )
{
VipsObjectClass *object_class = (VipsObjectClass *) class;
VipsFormatClass *format_class = (VipsFormatClass *) class;
object_class->nickname = "myformat";
object_class->description = _( "My format" );
format_class->is_a = is_myformat;
format_class->header = my_header;
format_class->load = my_read;
format_class->save = my_write;
format_class->get_flags = my_get_flags;
format_class->priority = 100;
format_class->suffs = my_suffs;
}
static void
vips_format_vips_init( VipsFormatVips *object )
{
}
G_DEFINE_TYPE( VipsFormatVips, vips_format_vips, VIPS_TYPE_FORMAT );
char *
g_module_check_init( GModule *self )
{
im_format_t *format;
format = im_format_register( "myformat",
_( "My image format" ),
my_suffs,
is_myformat,
read_myformat_header,
read_myformat_image,
write_myformat,
NULL
};
im_format_set_priority( format, 100 );
// register the type
vips_format_vips_get_type();
}
\end{verbatim}
\caption{Registering a format in a plugin}
@ -109,22 +119,21 @@ g_module_check_init( GModule *self )
\subsection{Finding a format}
You can loop over the format table in order with \verb+im_format_map()+. Like
You can loop over the format table in order with \verb+vips_format_map()+. Like
all the map functions in VIPS, this take a function and applies it to every
element in the table until it returns non-zero, or until the table has been
all covered.
element in the table until it returns non-zero, or until the table ends.
You find an \verb+im_format_t+ to use to open a file with
\verb+im_format_for_file()+. This searches the VIPS format table and returns
You find an \verb+VipsFormatClass+ to use to open a file with
\verb+vips_format_for_file()+. This searches the type system and returns
the first format whose test function returns true, setting an error message
and returning NULL if no format is found.
You find a format to write a file with \verb+im_format_for_name()+. This
You find a format to write a file with \verb+vips_format_for_name()+. This
returns the first format with a save function whose suffix list matches the
suffix of the supplied filename.
\subsection{Convenience functions}
A pair of convenience functions, \verb+im_format_write()+ and
\verb+im_format_read()+, will copy an image to and from disc using the
A pair of convenience functions, \verb+vips_format_write()+ and
\verb+vips_format_read()+, will copy an image to and from disc using the
appropriate format.

4
include/vips/format.h
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@ -54,8 +54,8 @@ extern "C" {
* im_format_flags_fn(). 0 is default.
*/
typedef enum {
VIPS_FORMAT_FLAG_NONE = 0, /* No flags set */
VIPS_FORMAT_FLAG_PARTIAL = 1 /* Lazy read OK (eg. tiled tiff) */
VIPS_FORMAT_NONE = 0, /* No flags set */
VIPS_FORMAT_PARTIAL = 1 /* Lazy read OK (eg. tiled tiff) */
} VipsFormatFlags;
/* Function protos for formats.

2
libsrc/format/format.c
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@ -125,7 +125,7 @@ vips2file( IMAGE *im, const char *filename )
static VipsFormatFlags
vips_flags( const char *filename )
{
return( VIPS_FORMAT_FLAG_PARTIAL );
return( VIPS_FORMAT_PARTIAL );
}
/* Vips format adds no new members.

2
libsrc/format/im_analyze2vips.c
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@ -586,7 +586,7 @@ static const char *analyze_suffs[] = { ".img", ".hdr", NULL };
static VipsFormatFlags
analyze_flags( const char *filename )
{
return( VIPS_FORMAT_FLAG_PARTIAL );
return( VIPS_FORMAT_PARTIAL );
}
/* analyze format adds no new members.

2
libsrc/format/im_exr2vips.c
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@ -456,7 +456,7 @@ exr_flags( const char *filename )
flags = 0;
if( isexrtiled( filename ) )
flags |= VIPS_FORMAT_FLAG_PARTIAL;
flags |= VIPS_FORMAT_PARTIAL;
return( flags );
}

2
libsrc/format/im_ppm2vips.c
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@ -496,7 +496,7 @@ ppm_flags( const char *filename )
flags = 0;
if( isppmmmap( filename ) )
flags |= VIPS_FORMAT_FLAG_PARTIAL;
flags |= VIPS_FORMAT_PARTIAL;
return( flags );
}

2
libsrc/format/im_tiff2vips.c
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@ -1545,7 +1545,7 @@ tiff_flags( const char *filename )
flags = 0;
if( istifftiled( filename ) )
flags |= VIPS_FORMAT_FLAG_PARTIAL;
flags |= VIPS_FORMAT_PARTIAL;
return( flags );
}

109
man/VipsFormat.3
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@ -9,24 +9,44 @@ load and search image formats
typedef enum {
.br
VIPS_FORMAT_FLAG_NONE = 0,
VIPS_FORMAT_NONE = 0,
.br
VIPS_FORMAT_FLAG_PARTIAL = 1
VIPS_FORMAT_PARTIAL = 1
.br
} VipsFormatFlags;
typedef struct _VipsFormatClass {
.br
VipsObjectClass parent_class;
gboolean (*is_a)( const char * );
.br
int (*header)( const char *, IMAGE * );
.br
int (*load)( const char *, IMAGE * );
.br
int (*save)( IMAGE *, const char * );
.br
VipsFormatFlags (*get_flags)( const char * );
.br
int priority;
.br
const char **suffs;
.br
} VipsFormatClass;
void *vips_format_map( VSListMap2Fn fn, void *a, void *b );
.br
VipsFormatClass *vips_format_for_file( const char *filename );
.br
VipsFormatClass *vips_format_for_name( const char *filename );
int im_format_write( IMAGE *im, const char *filename );
int vips_format_write( IMAGE *im, const char *filename );
int im_format_read( const char *filename, IMAGE *out );
int vips_format_read( const char *filename, IMAGE *out );
.SH DESCRIPTION
These functions register and unregister image formats, and search the table of
These functions search the
available image formats to find one suitable for loading or saving a file.
.B im_open(3)
@ -36,39 +56,29 @@ than copying to a descriptor you supply.
The two APIs are useful in different circumstances:
.B im_open(3)
is good if you want to directly manipulate a file on disc, for example with
the paintbox functions. The format API is useful for controlling how a image
the paintbox functions. On the other hand, this format API is useful for
controlling how a image
is unpacked, since you can specify a destination for the copy.
.B im_format_register(3)
registers an image format with vips. This might typically be called during
module load, see the documentation for GModule.
Image formats are subclasses of
.B VipsFormat
as outlined above. They are expected to implement at least one of the methods.
They should also set values for the
.B nickname
and
.B description
members of
.B VipsObject.
An image format has a number of components:
Other members are:
.B name
The internal name by which the format should be known. For example, the
OpenEXR image format is known within vips as "exr". You can identify formats
by testing this field with
.B strcmp(3).
.B name_user
The name as it should be displayed to the user. It can be internationalised.
For example, in English, the "analyze" format is shown as "Analyze 6.0".
.B suffs
A NULL-terminated array of possible file-name suffixes for this format. This
list is used to filter filenames when they are shown to the user, and to help
select a format to sav a file as. For example, the JPEG format has the
suffixes:
.B { ".jpg", ".jpeg", ".jpe", NULL }
.B is_a
.B is_a()
A function which tests whether a file is of the specified format. This is
useful if you can guess a file type from the first few bytes in the file. If
you leave this function NULL, vips will guess from the filename suffix for
you.
.B header
.B header()
Load only the image header, not any of the image pixels. vips will call this
first on
.B im_open(3)
@ -77,54 +87,53 @@ use the
.B load
function.
.B load
.B load()
Load the image from the file into the IMAGE. You can leave this function NULL
if you only have a
.B save
.B save()
method implemented.
.B save
.B save()
Write from the IMAGE to the file in this format. You can leave this function
NULL if you only have a lload method implemented.
NULL if you only have a load method implemented.
.B flags
A function which examines the file and sets various flags to indicated
.B get_flags()
A function which examines the file and sets various flags to indicate
properties of the image. The only flag implemented at the moment is
.B IM_FORMAT_FLAG_PARTIAL
.B VIPS_FORMAT_PARTIAL
which may be set to indicate that the file can be read lazily.
vips registers the format and returns a pointer to the
.B im_format_t
it created. This may later be used to unregister the format.
.B im_format_set_priority(3)
.B priority
sets a priority for the format. Priorities for formats default to zero: you
mmay set a lower or higher number to set where in the format table your format
is positioned.
.B im_format_unregister(3)
removes a format from vips. It mmight typically be called during module
unload, see the documentation for GModule.
.B suffs
A NULL-terminated array of possible file-name suffixes for this format. This
list is used to filter filenames when they are shown to the user, and to help
select a format to sav a file as. For example, the JPEG format has the
suffixes:
.B { ".jpg", ".jpeg", ".jpe", NULL }
.B im_format_map(3)
maps a function over the list of loaded formats. See
.B vips_format_map(3)
maps a function over the list of available formats. See
.B im_slist_map(3).
.B im_format_for_file(3)
.B vips_format_for_file(3)
looks at a file on disc and selects the 'best' format to use to load that
file. If no suitable format is found, it returns NULL and sets an error
message.
.B im_format_for_name(3)
.B vips_format_for_name(3)
looks at a filename and picks a format to use to save that file based on the
file extension. If no suitable format is found, it returns NULL and sets an
error message.
.B im_format_read(3)
.B vips_format_read(3)
is a convenience function which copies the image from the file into the IMAGE.
error, it returns non-zero and sets an error message.
.B im_format_write(3)
.B vips_format_write(3)
is a convenience function which copies the image to the file in the
appropriate format. On error, it returns non-zero and sets an error message.