Re: [ooc-compiler] C interface problems

[August <fus...@te...>]

Hello Stewart,

Yes, it worked! Thank you. (Not so obvious to use Pascal calling 
convention with a C library).

I also skimmed through your GL.Mod file and noticed that literal 
values are defined for (macro) constants. Isn't it possible for the 
OOC compiler to get the values from the C header file? Moreover I tend 
to dislike all but the absolutely necessary Oberon-2 extensions*, so I 
would prefer to rename all identifiers to valid Oberon-2 identifiers 
(no underscores) that follows the standard naming scheme and keep the 
definitions in three different modules: GL.Mod, Glu.Mod and Glut.Mod. 
The conversion rules are very regular (thanks to the regularity of the 
OpenGL interface):

Constants - Remove the prefix, lower case the first word, capitalize 
the following words (if any) and remove the underscores, e.g. 
GL_COLOR_BUFFER_BIT becomes colorBufferBit. There also exists a 
tradition to use Pascal case (rather than camel case) with exported 
variables and constants. Have not decided which is the best choice.

Types - Remove the prefix and capitalize, e.g. GLclampf becomes 
Clampf.

Variables - (No exported variables, right?)

Functions - Just remove the prefix, e.g. glutSwapBuffers becomes 
SwapBuffers.

-- August

*If we want Oberon-2 with lots of extensions then we might as well 
turn to Eiffel.

----- Original Message ----- 
From: "Stewart Greenhill" <sgr...@ii...>
To: "August" <fus...@te...>
Cc: <ooc...@li...>
Sent: Thursday, November 04, 2004 1:20 PM
Subject: Re: [ooc-compiler] C interface problems


> Hi August,
>
>> One potential problem: the glut functions are defined as 
>> "APIENTRY", which under Windows means that they use the "stdcall" 
>> calling convention rather than "cdecl". Therefore, you should 
>> probably specify "Pascal" rather than "C" as your interface type. 
>> That is:
>>   MODULE Glut [INTERFACE "Pascal"; LINK LIB "glut32"; LIB 
>> "opengl32"; END];
>> I think the same goes for the other GL modules. Presuming that the 
>> linker knows the procedure attributes, that may be why it is giving 
>> the error (ie. the procedure name matches, but the attributes are 
>> wrong).
>
> I ran a quick check, and it looks like this is indeed what happens. 
> The following should compile and link fine. It also runs OK, opening 
> a window and correctly calling the display procedure.
>
> MODULE Test;
>   IMPORT C, Glut;
>   VAR w: C.int;
>   PROCEDURE Display ["Pascal"];
>   END Display;
> BEGIN
>   w := Glut.CreateWindow("OpenGL Test");
>   Glut.DisplayFunc(Display);
>   Glut.MainLoop
> END Test.
>
> MODULE Glut [INTERFACE "Pascal"; LINK LIB "glut32"; LIB "opengl32"; 
> END];
>   IMPORT C;
> TYPE
>   DisplayCallback = PROCEDURE;
>
>   PROCEDURE ["glutCreateWindow"] CreateWindow*(title: ARRAY OF 
> C.char): C.int;
>   PROCEDURE ["glutDisplayFunc"] DisplayFunc*(p: DisplayCallback);
>   PROCEDURE ["glutMainLoop"] MainLoop*;
> END Glut.
>
> Hope this helps.
>
> Cheers,
>   Stewart
>