cannot create opengl by dynamically loading wayland symbols from library

[Jasper St. Pierre]

On Wed, Apr 16, 2014 at 2:27 PM, Pekka Paalanen <ppaalanen at gmail.com> wrote:

> Hi,
>
> I'm moving this conversation to where it belongs.
>
> On Wed, 16 Apr 2014 11:25:26 +0000
> bugzilla-daemon at freedesktop.org wrote:
>
> > https://bugs.freedesktop.org/show_bug.cgi?id=77521
> >
> >           Priority: medium
> >             Bug ID: 77521
> >           Assignee: wayland-bugs at lists.freedesktop.org
> >            Summary: cannot create opengl by dynamically loading wayland
> >                     symbols from library
> >           Severity: blocker
> >     Classification: Unclassified
> >                 OS: All
> >           Reporter: pulkitnandan at gmail.com
> >           Hardware: All
> >             Status: NEW
> >            Version: 1.3.0
> >          Component: wayland
> >            Product: Wayland
> >
> > I was trying to implement a window system agnostic library which will be
> used
> > in creating opengl apps with different windows systems. Lets name that
> library
> > as WSAL.Now to achieve this WSAL implements window system interfaces
> which is
> > used in creating native windows etc of specific window system while egl
> calls
> > are in main WSAL library.Consider wayland and X as examples of such two
> > libraries. As I separate several implementations of wayland and and X
> from
> > different team members.So to test them efficiently I have to create
> several
> > function pointers and object pointers that are present in those library
> > implementations and load them with symbols from libraries using dlsym
> utility
> > so that at compile time I donot have to link with any library.
> >
> > For X I was successfully in creating X backend.
> > For wayland I first got stuck at functions which are inline in
> > wayland_client_protocol.h. For them I cannot do the same.Instead I
> created a
> > function pointer which these functions actually calls in inline
> definition.
> >
> > Like when wl_display_get_registry is called wl_proxy_marshal_constructor
> is
> > ultimately called.
> >
> > The terrible fucntions are wl_proxy_marshal_constructor and
> wl_proxy_marshal as
> > they are defined with variable arguments.So I declared
> > new_wl_proxy_marshal_constructor a function pointer of same type as
> > wl_proxy_marshal_constructor and loaded the symbol from library using
> dlsym
> > into new_wl_proxy_marshal_constructor.
> >
> > But faced a fundamental problem of determing argument types as these
> terrible
> > functions (TFs) don't have constant argument signature i.e it may
> sometime pass
> > a int as its 4th aguments in one inline expansion while a char * in some
> other
> > inline function.
>
> Why do you need to know the arguments?
> Why cannot you just use it as is, with variable arguments?
>
> Btw. if the generated inline wrapper functions do not suit you, I
> think you could generate your own from the XML files, that end up
> calling the real functions exported from libwayland-client. That is
> how bindings to other programming languages are supposed work to my
> understanding.
>

This won't work with EGL, as EGL expects libwayland-client. It's the same
issue with X11: you can't just use XCB because GLX expects Xlib's Display /
Window pointers.


> > So I explored this wl_proxy_marshal_constructor which actually calls
> > wl_proxy_marshal_array_constructor after forming a variable arguments to
> a
> > single argument using some wl_proxy object signature which I have no
> access to
> > in main wayland interface.
> >
> > dlsym option of using rtld_now doesnot work.
> >
> > How to implement such functionality in wayland or provide a way to
> create a app
> > with no linking at build time.
>
> Have you looked at SDL2?
> http://hg.libsdl.org/SDL/file/tip/src/video/wayland
>
> To me it seems like it uses dlopen and dlsym equivalents to load
> Wayland libraries. I don't know if it is complete or in use yet,
> there seems to be also a non-dlopen path.
>
>
> Thanks,
> pq
> _______________________________________________
> wayland-devel mailing list
> wayland-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/wayland-devel
>



-- 
  Jasper
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