68 lines
2.6 KiB
XML
68 lines
2.6 KiB
XML
<?xml version="1.0"?>
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<!-- vim: set ts=2 sw=2 expandtab: -->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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]>
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<refentry id="binding">
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<refmeta>
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<refentrytitle>Writing bindings for libvips</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>Binding</refname>
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<refpurpose>How to write bindings for libvips</refpurpose>
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</refnamediv>
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<refsect1 id="binding-goi">
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<title>Binding and gobject-introspection</title>
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<para>
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The C source code
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to libvips has been marked up with special comments describing the
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interface in a standard way. These comments are read by
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gobject-introspection
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when libvips is compiled and used to generate a
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typelib, a description of how to call the library. Many languages have
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gobject-introspection packages: all you need to do to call libvips
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from your favorite language is to start g-o-i, load the libvips typelib,
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and you should have the whole library available. For example, from
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Python it's as simple as:
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<programlisting language="Python">
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from gi.repository import Vips
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</programlisting>
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</para>
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<para>
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libvips used in this way is likely to be rather bare-bones. For Python,
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we wrote a set of overrides which layer a more Pythonesque interface
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on top of the one provided for libvips by pygobject. These overrides
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are simply a set of Python classes.
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</para>
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<para>
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To call a vips operation, you'll need to make a new operation with
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vips_operation_new() (all it does is look up the operation by name
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with vips_type_find(), then call g_object_new() for you), then
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use vips_argument_map() and friends to loop over the operation's
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arguments setting them. Once you have set all arguments, use
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vips_cache_operation_build() to look up the operation in the cache
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and either build or dup it. If something goes wrong, you'll need
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to use vips_object_unref_outputs() and g_object_unref() to free the
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partially-built object.
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The Python binding uses this technique to implement a function which
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can call any vips operation, turning optional vips arguments into
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Python keyword arguments.
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</para>
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<para>
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If your language does not have a gobject-introspection package, you'll
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need to write something in C or C++ doing approximately the same thing.
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The C++ API takes this route.
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</para>
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</refsect1>
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</refentry>
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