Re: Extending LuaJIT ffi.load library?

[Michal Kottman <k0mpjut0r@...>]

2011/12/21 Adam Strzelecki <ono@java.pl>:
> Hi,
>
> I am trying to do some OpenGL via LuaJIT FFI. I've made 'gl' module that does cdef from gl.h file and and returns ffi.load('GL'). One can use it via `local gl = require('gl')`. Everything works great so far (using GLUT as well).
>
> Now I want to provide some convenience functions for OpenGL functions expecting non-simple pointer types, such as glMaterialfv, so instead calling:
>
>  gl.glMaterialfv(g.GL_FRONT, g.GL_SPECULAR,  ffi.new('GLfloat[4]', 1, 1, 1, 1));
>
> One can call without using ffi (hiding ffi internals):
>  gl.glMaterial(g.GL_FRONT, g.GL_SPECULAR, 1, 1, 1, 1)
>
> When I try to make my wrapped using:
>  gl.glMaterial = function(where, type, …)
>
> I get missing declaration for symbol 'glMaterial' in function '__newindex'. This is expected as 'gl' isn't a table. But then alternatively to have single namespace I could just remap all functions into new table:
>  M.function = glffi.glFunction
>
> Such table could be extended with new entries for convenience functions and will make code look clear & pretty and be extensible, but will kill probably lookup overhead elimination as well (not recommended in http://luajit.org/ext_ffi_tutorial.html#cache).
>
> So what would be the best solution? Anyone of you had similar problem? What was the solution in your case?

I had a similar problem with OpenCL. I am using the OpenCL FFI
bindings created by Dimiter Stanev [1]. There are some Lua functions
that I would like to export from the module, but for the rest I want
to use the C functions from the OpenCL library.

I solved it by creating the Lua functions in an extra table and
setting metatable __index to lookup in OpenCL namespace:

local ffi  = require( "ffi" )
local cl   = ffi.load( "OpenCL" )
local ext = {} -- this will be the returned module

-- extra function go into the `ext` table
function ext.GetPlatforms() ... end
function ext.GetDevices(platform_id) ... end

-- setup metatable with __index on `ext` to look up functions in the
`cl` namespace
setmetatable(ext, {__index=cl})

-- return `ext` as the module
return ext


[1] https://github.com/malkia/ufo