Re: [Pnet-developers] Question about pnetc access to Xwindows

[Rhys Weatherley]

On Sunday 21 November 2004 09:47 am, James Michael DuPont wrote:
> Hi,
>
> I have restarted my effort to port the vcg graph layout tool to pnet
> (http://savannah.nongnu.org/projects/vcgdotgnu) and be able to run the
> graph layout engine and display with the xwindows. I hope to be able to
> use the great controls you have been working on to make nice C# driven
> GUIS for this tool.

In that case, you will need to use the Winforms API directly (with some kind 
of C wrapper around the C# classes presumably).  By-passing it to go direct 
to X11/Xsharp won't work.

> Currently I am able to compile now all the source from the project,
> including the access to the xwindows system after patching the compiler
> as described here (
> https://savannah.gnu.org/bugs/index.php?func=detailitem&item_id=11068)

Changing an error into a warning is not a fix.  The real fix would be to 
modify "BinarySem", "RelationalSem", and other similar functions in 
"c_oper.tc" to mark the output of an operator as a dynamic constant if either 
operand is a dynamic constant and the other is a normal or dynamic constant.  
A potential change will be needed wherever "ILNode_EvalConst" is called in 
that file (there are a lot of affected operators).  Please try again (and 
yes, I'm asking you to attempt this).

> Now, the problem is linking :
>
> When I compile the code that calls X from c, it produces a call like
> this :
>
> call       valuetype _XDisplay * '<ModuleExtern>'::XOpenDisplay(int8
> modopt([OpenSystem.C]OpenSystem.C.IsConst) *)
>
> But the code in the  libXSharp has the following bindings :
> .namespace Xsharp {.method public static hidebysig pinvokeimpl("X11"
> cdecl ) native int XOpenDisplay(class System.String display_name) cil
> managed {}}
>
> I have taken that to produces a new .Il Binding like this :
> .namespace '<ModuleExtern>'{
>       .method public static hidebysig pinvokeimpl("X11" cdecl ) valuetype
> _XDisplay *   XOpenDisplay(
>               int8 modopt([OpenSystem.C]OpenSystem.C.IsConst) *
>               )  cil managed {}
> }
>
> That is able to link.

<ModuleExtern> is a directive to the linker to find the C function in any 
properly-marked module.  It should "just work" with the straight pinvoke 
declaration if you have marked "libXsharp" properly.  Which in this case, you 
haven't.  The file "pnet/doc/c_language_abi.html" describes all the marker 
attributes that you will need.

Rather than mess with raw IL, I suggest that you use the pnetC compiler to 
generate the pinvoke library layer.  Create a .c file with declarations such 
as follows:

    extern Display *XOpenDisplay(const char *display)
        __attribute__((__pinvoke__("X11"), __cdecl__));

Then compile that into dll library form using the pnetC compiler.  The result 
should have all of the proper markings to link correctly.

> I would like to know if this is right way to proceed, and If so, I will
> create Il bindings for all the needed X windows functions.

As I indicated, you won't get access to Winforms controls this way.  But if 
your app is bare X, then it may work.  But only on X11 systems.

Cheers,

Rhys.