more docs stuff
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John Cupitt
parent
7888526361
commit
2e3baa1bef
2
TODO
2
TODO
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@ -1,3 +1,5 @@
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- bicubic needs a signed int lut path with rounding in the other direction
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for negatives
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- vips_object_unref_outputs() needs docs ... bindings will need it
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@ -4,14 +4,14 @@
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]>
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<refentry id="using-from-c">
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<refmeta>
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<refentrytitle>Using VIPS from C</refentrytitle>
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<refentrytitle>VIPS from C</refentrytitle>
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<manvolnum>3</manvolnum>
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<refmiscinfo>VIPS Library</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>Using VIPS</refname>
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<refpurpose>How to use the VIPS library</refpurpose>
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<refpurpose>How to use the VIPS library from C</refpurpose>
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</refnamediv>
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<refsect1 id="using-C">
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@ -11,7 +11,7 @@
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<refnamediv>
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<refname>Using VIPS</refname>
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<refpurpose>How to use the VIPS library</refpurpose>
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<refpurpose>How to use the VIPS library from the command-line</refpurpose>
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</refnamediv>
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<refsect1 id="using-command-line">
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@ -77,7 +77,85 @@
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* <emphasis>Command-line interface</emphasis> Any vips object can be run from
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* the command-line with the `vips` driver program.
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*
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* ## The #VipsObject lifecycle
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*
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* #VipsObject s have a strictly defined lifecycle, split broadly as construct
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* and then use. In detail, the stages are:
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*
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* 1. g_object_new(). The #VipsObject is created with g_object_new(). Objects
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* in this state are blank slates and need to have their various parameters
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* set.
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*
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* 2. g_object_set(). You loop over the #VipsArgument that the object has
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* defined with vips_argument_map(). Arguments have a set of flags attached to
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* them for required, optional, input, output, type, and so on. You must set
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* all required arguments.
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*
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* 3. vips_object_build(). Call this to construct the object and get it ready
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* for use. Building an object happens in four stages, see below.
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*
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* 4. g_object_get(). The object has now been built. You can read out any
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* computed values.
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*
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* 5. g_object_unref(). When you are done with an object, you can unref it.
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* See the section on reference counting for an explanation of the convention
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* that #VipsObject uses. When the last ref to an object is released, the
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* object is closed. Objects close in three stages, see below.
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*
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* The stages inside vips_object_build() are:
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*
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* 1. Chain up through the object's @build class methods. At each stage,
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* each object does any initial setup and checking, then chains up to its
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* superclass.
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*
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* 2. The innermost @build method in #VipsObject itself checks that all input
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* arguments have been set and then returns.
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*
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* 3. All object @build methods now finish executing, from innermost to
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* outermost. They know all input arguments have been checked and supplied, so
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* now they set all output arguments.
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*
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* 4. vips_object_build() finishes the process by checking that all output
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* objects have been set, and then triggering the #VipsObject::postbuild
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* signal. #VipsObject::postbuild only runs if the object has constructed
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* successfuly.
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*
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* And the stages inside close are:
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*
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* 1. #VipsObject::preclose. This is emitted at the start of
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* the #VipsObject dispose. The object is still functioning.
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*
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* 2. #VipsObject::close. This runs just after all #VipsArgument held by
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* the object have been released.
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*
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* 3. #VipsObject::postclose. This runs right at the end. The object
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* pointer is still valid, but nothing else is.
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*
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* ## The #VipsOperation cache
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*
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* Because all #VipsObject are immutable, they can be cached. The cache is
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* very simple to use: instead of calling vips_object_build(), instead call
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* vips_cache_operation_build(). This function calculates a hash from the
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* operations's input arguments and looks it up in table of all recent
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* operations. If there's a hit, the new operation is unreffed, the old
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* operation reffed, and the old operation returned in place of the new one.
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*
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* The cache size is controlled with vips_cache_set_max() and friends.
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*
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* ## The #VipsObject reference counting convention
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*
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* #VipsObject has a set of conventions to simplify reference counting.
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*
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* 1. All input %GObject have a ref added to them, owned by the object. When a
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* #VipsObject is unreffed, all of these refs to input objects are
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* automatically dropped.
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*
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* 2. All output %GObject hold a ref to the object. When a %GObject which is an
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* output of a #VipsObject is disposed, it must drop this reference.
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* #VipsObject which are outputs of other #VipsObject will do this
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* automatically.
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*
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* See #VipsOperation for an example of #VipsObject reference counting.
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*
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*/
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@ -1504,6 +1582,13 @@ vips_object_class_init( VipsObjectClass *class )
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G_STRUCT_OFFSET( VipsObject, description ),
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"" );
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/**
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* VipsObject::postbuild:
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* @object: the object that has been built
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*
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* The ::postbuild signal is emitted once just after successful object
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* construction. Return non-zero to cause object construction to fail.
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*/
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vips_object_signals[SIG_POSTBUILD] = g_signal_new( "postbuild",
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G_TYPE_FROM_CLASS( class ),
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G_SIGNAL_RUN_LAST,
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@ -1511,6 +1596,14 @@ vips_object_class_init( VipsObjectClass *class )
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NULL, NULL,
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vips_INT__VOID,
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G_TYPE_INT, 0 );
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/**
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* VipsObject::preclose:
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* @object: the object that is to close
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*
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* The ::preclose signal is emitted once just before object close
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* starts. The oject is still alive.
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*/
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vips_object_signals[SIG_PRECLOSE] = g_signal_new( "preclose",
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G_TYPE_FROM_CLASS( class ),
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G_SIGNAL_RUN_LAST,
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@ -1518,6 +1611,14 @@ vips_object_class_init( VipsObjectClass *class )
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NULL, NULL,
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g_cclosure_marshal_VOID__VOID,
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G_TYPE_NONE, 0 );
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/**
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* VipsObject::close:
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* @object: the object that is closing
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*
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* The ::close signal is emitted once during object close. The object
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* is dying and may not work.
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*/
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vips_object_signals[SIG_CLOSE] = g_signal_new( "close",
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G_TYPE_FROM_CLASS( class ),
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G_SIGNAL_RUN_LAST,
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@ -1525,6 +1626,14 @@ vips_object_class_init( VipsObjectClass *class )
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NULL, NULL,
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g_cclosure_marshal_VOID__VOID,
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G_TYPE_NONE, 0 );
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/**
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* VipsObject::postclose:
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* @object: the object that has closed
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*
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* The ::postclose signal is emitted once after object close. The
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* object pointer is still valid, but nothing else.
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*/
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vips_object_signals[SIG_POSTCLOSE] = g_signal_new( "postclose",
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G_TYPE_FROM_CLASS( class ),
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G_SIGNAL_RUN_LAST,
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@ -94,11 +94,69 @@
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* vips_cache_operation_build() to look up the operation in the cache and
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* either build or dup it. If something goes wrong, you'll need to use
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* vips_object_unref_outputs() and g_object_unref() to free the
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* partially-built object.
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* partially-built object. See
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* <link linkend="binding">binding</link> for an introduction to libvips
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* introspection.
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*
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* Use vips_call_argv() to run any vips operation from a command-line style
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* argc/argv array. This is the thing used by the vips main program to
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* implement the vips command-line interface.
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*
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* ## #VipsOperation and reference counting
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*
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* After calling a #VipsOperation you are responsible for unreffing any output
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* objects. For example, consider:
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*
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* |[
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* VipsImage *im = ...;
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* VipsImage *t1;
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*
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* if (vips_invert (im, &t1, NULL))
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* error ..
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* ]|
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*
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* This will invert @im and return it as a new #VipsImage, @t1. As the caller
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* of vips_invert(), you are responsible for @t1 and must unref it when you no
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* longer need it. If vips_invert() fails, no @t1 is returned and you don't
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* need to do anything.
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*
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* Consider running two operations, one after the other. You could write:
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*
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* |[
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* VipsImage *im = ...;
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* VipsImage *t1, *t2;
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*
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* if (vips_invert (im, &t1, NULL)) {
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* g_object_unref (im);
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* return -1;
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* }
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* g_object_unref (im);
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*
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* if (vips_flip (t1, &t2, VIPS_DIRECTION_HORIZONTAL, NULL)) {
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* g_object_unref (t1);
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* return -1;
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* }
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* g_object_unref (t1);
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* ]|
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*
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* This is correct, but rather long-winded. libvips provides a handy thing to
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* make a vector of auto-freeing object references. You can write this as:
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*
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* |[
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* VipsObject *parent = ...;
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* VipsImage *im = ...;
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* VipsImage *t = (VipsImage **) vips_object_local_array (parent, 2);
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*
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* if (vips_invert (im, &t[0], NULL) ||
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* vips_flip (t[0], &t[1], VIPS_DIRECTION_HORIZONTAL, NULL))
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* return -1;
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* ]|
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*
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* where @parent is some enclosing object which will be unreffed when this
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* task is complete. vips_object_local_array() makes an array of #VipsObject
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* (or #VipsImage, in this case) where when @parent is freed, all non-NULL
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* #VipsObject in the array are also unreffed.
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*
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*/
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/**
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