Re: LuaJIT FFI only bindings for glfw, OpenCL, OpenGL

[David Given <dg@...>]

On 26/01/11 07:00, Henk Boom wrote:
[...]
> They don't exist in the .dll, or they don't exist in the header file?

Having worked with OpenGL extensions (mostly on egl), the answer to this
question is: both, possibly neither.

The prototypes for the extension functions are set in stone by
Khronos[*]. It's perfectly acceptable for the application to declare its
own prototypes (or even have its own copies of the header files, copied
from Khronos itself). It gets the function using *GetProcAddress(),
casts it to the appropriate type, and then it can call it. As a result,
it's completely undefined where the function itself resides. One
possible implementation is to have *GetProcAddress() dlopen() a shared
library with the given name so that the extensions get loaded on demand...


[*] ...eg:

GL_APICALL void GL_APIENTRY glExtGetShadersQCOM (GLuint *shaders, GLint
maxShaders, GLint *numShaders);

The GL_APICALL and GP_APIENTRY macros can be defined by the platform to
provide platform-specific tweaks to the ABI. Normally GL_APICALL is
defined to 'extern' or '__declspec(dllimport)' and GL_APIENTRY to a
compiler-specific calling convention specifier like '__stdcall' or
'__ccall'. Which of course means that the ABI can vary drastically
depending on how your OpenGL library has been built, even on a single
platform, which means that maintaining an FFI-compatible repository of
function prototypes isn't adequate.

Fun, eh?

-- 
┌─── ｄｇ＠ｃｏｗｌａｒｋ．ｃｏｍ ───── http://www.cowlark.com ─────
│
│ life←{ ↑1 ⍵∨.^3 4=+/,¯1 0 1∘.⊖¯1 0 1∘.⌽⊂⍵ }
│ --- Conway's Game Of Life, in one line of APL

Attachment: signature.asc
Description: OpenPGP digital signature