Writing bindings for libvips
Binding — How to write bindings for libvips
Binding and gobject-introspection
The C source code to libvips has been marked up with special comments describing the interface in a standard way. These comments are read by gobject-introspection when libvips is compiled and used to generate a typelib, a description of how to call the library. Many languages have gobject-introspection packages: all you need to do to call libvips from your favorite language is to start g-o-i, load the libvips typelib, and you should have the whole library available. For example, from Python it's as simple as:
from gi.repository import Vips
libvips used in this way is likely to be rather bare-bones. For Python, we wrote a set of overrides which layer a more Pythonesque interface on top of the one provided for libvips by pygobject. These overrides are simply a set of Python classes.
To call a vips operation, you'll need to make a new operation with
vips_operation_new() (all it does is look up the operation by name
vips_type_find(), then call
g_object_new() for you), then
vips_argument_map() and friends to loop over the operation's
arguments setting them. Once you have set all arguments, use
vips_cache_operation_build() to look up the operation in the cache
and either build or dup it. If something goes wrong, you'll need
g_object_unref() to free the
The Python binding uses this technique to implement a function which
can call any vips operation, turning optional vips arguments into
Python keyword arguments.
If your language does not have a gobject-introspection package, you'll need to write something in C or C++ doing approximately the same thing. The C++ API takes this route.
You can generate searchable docs from a
.gir (the thing that
is built from scanning libvips and which in turn turn the typelib is
made from) with g-ir-doc-tool, for example:
$ g-ir-doc-tool --language=Python -o ~/mydocs Vips-8.0.gir
Then to view them, either:
$ yelp ~/mydocs
$ cd ~/mydocs $ yelp-build html .
To make HTML docs. This is an easy way to see what you can call in the library.