Language bindings for wl_registry_bind request

[Daniel Stone]

Hi,

On Thu, 18 Jun 2020 at 07:25, Brad Robinson
<brobinson at toptensoftware.com> wrote:
> I'm putting together a set of C# bindings for Wayland and it's coming along nicely but I've hit an issue with wl_registry_bind where its implementation doesn't seem to match the xml.
>
> The wayland.xml file declares it as: (essentially one input parameter - name)
>
>     <request name="bind">
>       <description summary="bind an object to the display">
> Binds a new, client-created object to the server using the
> specified name as the identifier.
>       </description>
>       <arg name="name" type="uint" summary="unique numeric name of the object"/>
>       <arg name="id" type="new_id" summary="bounded object"/>
>     </request>
>
>
> But the C implementation has additional version and interface parameters and uses the wl_proxy_marshal_constructor_versioned - with apparently no hints in the xml as to why.
>
> [...]
>
> Similarly the xml file would suggest the message signature should be "un", but the C bindings have it as "usun".
>
> What's going on here?  Is this a special case for this one method?

Yeah, new_id with no interface gets expanded to new_id + interface
name + version:
    https://gitlab.freedesktop.org/wayland/wayland/-/blob/master/src/scanner.c#L1233

Theoretically it applies to anything with that property, but in
reality the only user is wl_registry.bind.

It is generally not recommended to write your own bindings from
scratch, however. When you need to integrate with EGL, you need to
pass a pointer to the struct wl_display * for an EGLDisplay, and to
wl_surface * for an EGLSurface (via wl_egl_surface). Mesa internally
uses the C version of libwayland to send requests and receive events -
which will obviously not work with the C# implementation. The same is
true of Vulkan, GStreamer, and other libraries which integrate with
Wayland.

The recommended approach, avoiding these issues, is to wrap the
Wayland library using the 'dispatcher' methods provided; there is more
background here: https://smithay.github.io/wayland-rs-v-0-21.html

Cheers,
Daniel