[libcamera-devel] [PATCH] gstreamer: Add meson devenv support

[Laurent Pinchart]

Hi Nicolas,

Thank you for the patch.

On Tue, Dec 05, 2023 at 09:00:10AM -0500, Nicolas Dufresne via libcamera-devel wrote:
> Le lundi 04 décembre 2023 à 16:27 -0500, Nicolas Dufresne via libcamera-devel a écrit :
> > From: Nicolas Dufresne <nicolas.dufresne at collabora.com>
> > 
> > This change to the build system will prepend the plugin build directory
> > to GST_PLUGIN_PATH environment. This makes the built plugin visible to
> > GStreamer inside meson devenv enabling uninstalled testing.
> 
> In case of positive feedback, I'd like to make a V2 that updates the
> documentation. Instead of:
> 
>   export GST_PLUGIN_PATH=$(pwd)/build/src/gstreamer
> 
> I'd document:
> 
>   meson devenv -C build/
> 
> Devenv is nicer since it prepends to the path, it will also blend well if
> libcamera is made a subproject of another project using devenv (notably mesa
> and/or GStreamer). In cross-compilation, the env can be generated on the build
> computer, and used as a script on the target with help of the --dump option.

I didn't know about meson devenv, it seems to be an interesting feature.
We have a bit of code in libcamera and in the unit tests to explicitly
support running the libcamera test executables and the unit tests from
the build directory and find the correct resources. I would be happy to
remove that if it could be replaced by meson devenv.

Related to this patch, we have the following code in
test/gstreamer/gstreamer_test.cpp:

	/*
	 * Remove the system libcamera plugin, if any, and add the plugin from
	 * the build directory.
	 */
	GstRegistry *registry = gst_registry_get();
	g_autoptr(GstPlugin) plugin = gst_registry_lookup(registry, "libgstlibcamera.so");
	if (plugin)
		gst_registry_remove_plugin(registry, plugin);

	std::string path = libcamera::utils::libcameraBuildPath() + "src/gstreamer";
	if (!gst_registry_scan_path(registry, path.c_str())) {
		g_printerr("Failed to add plugin to registry\n");

		status_ = TestFail;
		return;
	}

Do you think this could be dropped ? I haven't checked if the meson unit
tests are run in a similar environment as devenv though.

> > ---
> >  src/gstreamer/meson.build | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/src/gstreamer/meson.build b/src/gstreamer/meson.build
> > index 20784b71..3810a15b 100644
> > --- a/src/gstreamer/meson.build
> > +++ b/src/gstreamer/meson.build
> > @@ -46,3 +46,10 @@ libcamera_gst = shared_library('gstlibcamera',
> >      install : true,
> >      install_dir : '@0@/gstreamer-1.0'.format(get_option('libdir')),
> >  )
> > +
> > +# Makes the plugin visble to GStreamer inside meson devenv
> > +fs = import('fs')
> > +plugin_path = fs.parent(libcamera_gst.full_path())
> > +env = environment()
> > +env.prepend('GST_PLUGIN_PATH', fs.parent(plugin_path))
> > +meson.add_devenv(env)

-- 
Regards,

Laurent Pinchart