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<title>VIPS_OBJECT(3) manual page</title>
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<a href='#toc'>Table of Contents</a><p>
<h2><a name='sect0' href='#toc0'>Name</a></h2>
VipsObject, vips_object_build, vips_object_print_class, vips_object_print,
vips_object_class_install_argument, vips_argument_map, vips_object_set_property,
vips_object_get_property, vips_object_new, vips_object_new_from_string,
vips_object_to_string - VIPS base class
<h2><a name='sect1' href='#toc1'>Synopsis</a></h2>
#include <vips/vips.h>
<p> /*
Flags we associate with each argument. <br>
*/<br>
<br>
typedef enum _VipsArgumentFlags { <br>
VIPS_ARGUMENT_NONE = 0,<br>
<p> /* Must be set in the constructor.<br>
<br>
*/<br>
<br>
VIPS_ARGUMENT_REQUIRED = 1,<br>
<p> /* Can only be set in the constructor.<br>
<br>
*/<br>
<br>
VIPS_ARGUMENT_CONSTRUCT = 2,<br>
<p> /* Can only be set once.<br>
<br>
*/<br>
<br>
VIPS_ARGUMENT_SET_ONCE = 4,<br>
<p> /* Have input & output flags. Both set is an error; neither set <br>
<br>
* is OK.<br>
<br>
*/<br>
<p> /* Is an input argument (one we depend on) ... if it’s a gobject, we <br>
<br>
* should ref it. In our _dispose(), we should unref it.<br>
<br>
*/<br>
<br>
VIPS_ARGUMENT_INPUT = 8,<br>
<p> /* Is an output argument (one that depends on us) ... if it’s a<br>
<br>
* gobject, we should ref ourselves. We watch "destroy" on the<br>
<br>
* argument: if it goes, we unref ourselves. If we dispose, we<br>
<br>
* disconnect the signal.<br>
<br>
*/<br>
<br>
VIPS_ARGUMENT_OUTPUT = 16<br>
<br>
} VipsArgumentFlags;
<p> /* Useful flag combinations. User-visible ones are:
<p> VIPS_ARGUMENT_REQURED_INPUT <tt> </tt> <tt> </tt> Eg. the "left" argument for add
<p> VIPS_ARGUMENT_OPTIONAL_INPUT
<tt> </tt> <tt> </tt> Eg. the "caption" for an object
<p> VIPS_ARGUMENT_REQURED_OUTPUT <tt> </tt> <tt> </tt> Eg. the "result"
<p>of an add operation
<p> VIPS_ARGUMENT_OPTIONAL_OUTPUT <tt> </tt> <tt> </tt> Eg. the "width" of an
<p>image
<p> Other combinations are used internally, eg. supplying the cast-table
<br>
<br>
for an arithmetic operation<br>
<p> */<br>
<p> #define VIPS_ARGUMENT_REQUIRED_INPUT eg. supplying the cast-table <br>
(VIPS_ARGUMENT_INPUT | VIPS_ARGUMENT_REQUIRED | <br>
<br>
VIPS_ARGUMENT_CONSTRUCT | VIPS_ARGUMENT_SET_ONCE)<br>
<p> #define VIPS_ARGUMENT_OPTIONAL_INPUT <br>
(VIPS_ARGUMENT_INPUT | <br>
<br>
VIPS_ARGUMENT_CONSTRUCT | VIPS_ARGUMENT_SET_ONCE)<br>
<p> #define VIPS_ARGUMENT_REQUIRED_OUTPUT <br>
(VIPS_ARGUMENT_OUTPUT | VIPS_ARGUMENT_REQUIRED | <br>
<br>
VIPS_ARGUMENT_SET_ONCE)<br>
<p> #define VIPS_ARGUMENT_OPTIONAL_OUTPUT <br>
(VIPS_ARGUMENT_OUTPUT | <br>
<br>
VIPS_ARGUMENT_SET_ONCE)<br>
<p> /* Keep one of these for every argument. <br>
*/<br>
<br>
typedef struct _VipsArgument { <br>
GParamSpec *pspec;<tt> </tt> <tt> </tt> /* pspec for this argument */<br>
<p> /* More stuff, see below */<br>
<br>
} VipsArgument;
<p> typedef void *(*VipsArgumentMapFn)( VipsObject *, GParamSpec
*, <br>
VipsArgumentClass *, VipsArgumentInstance *, void *a, void *b );<br>
<br>
void *vips_argument_map( VipsObject *object, <br>
VipsArgumentMapFn fn, void *a, void *b );<br>
<p> struct _VipsObject { <br>
GObject parent_object;<br>
<p> };
<p> struct _VipsObjectClass { <br>
GObjectClass parent_class;<br>
<p> /* Build the object ... all argument properties have been set,<br>
<br>
* now build the thing.<br>
<br>
*/<br>
<br>
int (*build)( VipsObject *object );<br>
<p> /* Try to print something about the class, handy for help displays.<br>
<br>
*/<br>
<br>
void (*print_class)( struct _VipsObjectClass *, VipsBuf * );<br>
<p> /* Try to print something about the object, handy for debugging.<br>
<br>
*/<br>
<br>
void (*print)( VipsObject *, VipsBuf * );<br>
<p> /* Class nickname, eg. "VipsInterpolateBicubic" has "bicubic" as a<br>
<br>
* nickname. Not internationalised. <br>
<br>
*/<br>
<br>
const char *nickname;<br>
<p> /* Class description. Used for help messages, so internationalised.<br>
<br>
*/<br>
<br>
const char *description;<br>
<p> };
<p> void vips_object_set_property( GObject *gobject, <br>
guint property_id, const GValue *value, GParamSpec *pspec );<br>
<br>
void vips_object_get_property( GObject *gobject, <br>
guint property_id, GValue *value, GParamSpec *pspec );<br>
<p> int vips_object_build( VipsObject *object ); <br>
void vips_object_print_class( VipsObjectClass *klass ); <br>
void vips_object_print( VipsObject *object );
<p> void vips_object_class_install_argument(
VipsObjectClass *, <br>
GParamSpec *pspec, VipsArgumentFlags flags, guint offset );<br>
<p> typedef void *(*VipsObjectSetArguments)( VipsObject *, <br>
void *, void * );<br>
<br>
VipsObject *vips_object_new( GType type, <br>
VipsObjectSetArguments set, void *a, void *b );<br>
<p> VipsObject *vips_object_new_from_string( const char *base, <br>
const char *str );<br>
<br>
void vips_object_to_string( VipsObject *object, VipsBuf *buf );
<p>
<h2><a name='sect2' href='#toc2'>Description</a></h2>
<b>VipsObject</b>
is the base class for VIPS. It provides some common features, like class
nicknames, and implements an extension to <b>GObject</b> for properties to let
them be used more like function arguments.
<p> <b>VipsObject</b> is still being developed,
so this documentation only covers enough of the interface to let you use
the classes that have been built on top of <b>VipsObject:</b> <b>VipsInterpolate</b>
and <b>VipsFormat.</b> Hopefully the next version will be more fleshed out.
<p> <b>VipsObject</b>
adds two properties: <b>nickname</b> and <b>description.</b> They are actually class
properties, but are available as instance properties too for convenience.
<p> <b>nickname</b> is the non-internationalised nickname of the class and is used
to simplify lookup. For example, the <b>VipsInterpolateBicubic</b> class has the
nickname "bicubic".
<p> <b>description</b> is the internationalised short description
of the class. For example, the <b>VipsInterpolateBicubic</b> class might have the
description "bicubic interpolation (Catmull-Rom)".
<p> Like the rest of VIPS,
<b>VipsObject</b> is a functional type. You can set properties during object construction,
but not after that point. You may read properties at any time after construction,
but not before.
<p> To enforce these rules, VIPS extends the standard <b>GObject</b>
property system and adds a new phase to object creation.
<p> In class_init,
after creating a property, you make it into an argument by adding a call
to <a href='vips_object_class_install_argument.3.html'><b>vips_object_class_install_argument(3)</a>
. </b> This takes a set of flags, used
to tell VIPS what sort of argument this is, and an offset for the data
value in the class instance. For example:
<p> pspec = g_param_spec_string(
"description",<br>
_( "Description" ),<br>
_( "Class description" ),<br>
"",<br>
(GParamFlags) G_PARAM_READWRITE );<br>
g_object_class_install_property( gobject_class,<br>
PROP_DESCRIPTION, pspec );<br>
vips_object_class_install_argument( object_class, pspec,<br>
VIPS_ARGUMENT_SET_ONCE,<br>
G_STRUCT_OFFSET( VipsObject, description ) );<br>
<p> After <a href='g_object_new.3.html'><b>g_object_new(3)</b></a>
you can continue to set arguments. After you have
set all the ones you want to set, call <a href='vips_object_build.3.html'><b>vips_object_build(3)</b></a>
to check that
required arguments have been set, no arguments have been set many times,
and so on.
<p> Once a <b>VipsObject</b> has been built, you can no longer set arguments,
but you can read them.
<p> Use <a href='vips_argument_map.3.html'><b>vips_argument_map(3)</b></a>
to iterate over the arguments
for an object in the correct order. You can use this to discover the arguments
any class takes at runtime.
<p> <a href='vips_object_set_property.3.html'><b>vips_object_set_property(3)</b></a>
and <a href='vips_object_get_property.3.html'><b>vips_object_get_property(3)</b></a>
are used in subclasses of <b>VipsObject</b> to get and set object arguments. You
don’t need to implement your own get/set methods.
<p> <a href='vips_object_new.3.html'><b>vips_object_new(3)</b></a>
is
a convenience function which encapsulates the new/set/build sequence outlined
above.
<p> <a href='vips_object_new_from_string.3.html'><b>vips_object_new_from_string(3)</b></a>
is a convenience function which builds
an object from a set of arguments encoded as a string. It used used by the
VIPS command-line program to generate operation arguments.
<p> <a href='vips_object_to_string.3.html'><b>vips_object_to_string(3)</b></a>
is the exact inverse: it prints the string that would construct an object.
<p>
<h2><a name='sect3' href='#toc3'>Return Value</a></h2>
Unless otherwise noted, functions return 0 success and -1 on
error.
<h2><a name='sect4' href='#toc4'>See Also</a></h2>
<a href='VipsFormat.3.html'>VipsFormat(3)</a>
, <a href='VipsInterpolate.3.html'>VipsInterpolate(3)</a>
, <a href='vips_type_find.3.html'>vips_type_find(3)</a>
.
<h2><a name='sect5' href='#toc5'>Author</a></h2>
John
Cupitt <p>
<hr><p>
<a name='toc'><b>Table of Contents</b></a><p>
<ul>
<li><a name='toc0' href='#sect0'>Name</a></li>
<li><a name='toc1' href='#sect1'>Synopsis</a></li>
<li><a name='toc2' href='#sect2'>Description</a></li>
<li><a name='toc3' href='#sect3'>Return Value</a></li>
<li><a name='toc4' href='#sect4'>See Also</a></li>
<li><a name='toc5' href='#sect5'>Author</a></li>
</ul>
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