Export host C functions to luajit FFI without export
- From: Florian Wesch <fw@xxxxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Wed, 21 Jan 2015 12:06:33 +0100
Hi.
Here is another way of exporting host C functions without using
-rdynamic: Create a C-side static struct that contains the function
pointers you want to make available to Lua. Then call Lua with
a lightuserdata pointing to the address of that struct. In Lua,
use ffi.cdef to define the exact same struct and then use
ffi.cast to cast the lightuserdata to a Lua type. You can then
access the struct members and call your C functions.
I wrote a C macro (tested with gcc 4.6 on Linux) that makes
this easier. Hope it is useful:
#define LUA_C_EXPORT(L, name, api_typedef, ...) \
do { \
static struct { \
api_typedef \
} exports = { \
__VA_ARGS__ \
}; \
luaL_loadstring(L, \
"local ffi = require \"ffi\";" \
"ffi.cdef[[" \
"typedef struct {" \
#api_typedef \
"}" name ";" \
"]];" \
name " = ffi.cast(\"" name "*\", ...)" \
); \
lua_pushlightuserdata(L, &exports); \
lua_pcall(L, 1, 0, 0); \
} while (0)
Using it is simple:
LUA_C_EXPORT(L, "gl",
void (*PushMatrix)();
void (*PopMatrix)();
,
luaGlPushMatrix,
luaGlPopMatrix,
);
In Lua you can then use:
gl.PushMatrix()
Notice that there is no error checking for luaL_loadstring
and lua_pcall right now. Feedback appreciated.
Florian
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