Re: Conversion Lua function to C function

[Jiří Prymus <jiri.prymus@...>]

Yes, I know what do you think but this static approach, in  my case
will be better use dynamic algorithm.
But meantime I don't know how to do that.

I want to create algorithm where I can use something like this:

-- lua script--
cv=require('luacv')

function on_trackbar1(pos)
.... some update event stuff..
end

function on_trackbar2(pos)
...another update event stuff for another trackbar widget
end

cv.cvCreateTrackbar(name1,wndname1,edge1,100,"on_trackbar1")
cv.cvCreateTrackbar(name2,wndname2,edge2,100,"on_trackbar2")
-- end of lua --

And that is problem with my current implementation because stack
information and funcname will be rewritten
by second calling of cvCreateTrackbar(....) and C callback function
of first TrackBar will call lua callback function of second TrackBar.

Little confusing, isn't it? :)

With regards,
Jiri Prymus


2009/10/18 GrayFace <sergroj@mail.ru>:
> Instead of 1 you can also have 10 or 100 or 1000 callbacks, but a limited
> number of them.
> Like,
> void mycallback(int pos, int funcid)
> {
>     luaL_unref(...);
>     lua_rawgeti(state, -1, funcid);
>     lua_pushnumber(state,pos);
>     lua_call(state,1,0);
>     lua_pop(state, 1);
> }
>
> void mycallback_1(int pos) { mycallback(pos, 1); }
> ...
> void mycallback_100(int pos) { mycallback(pos, 100); }
>
>
>
>
>
> ----- Original Message ----- From: Jiří Prymus
> To: Lua list
> Sent: Sunday, October 18, 2009 9:25 PM
> Subject: Re: Conversion Lua function to C function
>
>
> Hi,
>
> thanks for great idea.
> But I have problem with lua_State *  in my_callback fuction, because
> it has only "int pos " as argument .
> It's defined like :
> typedef void (CV_CDECL *CvTrackbarCallback)(int pos);
>
> And only way to pass stack to callback function is in global variable,
> but this isn't so good technique as I hoped.
>
> But yes sample code like this works.
>
> ....
> lua_State *state;
> char funcname[100];
>
> void mycallback(int pos)
> {
>     lua_pushstring(state,funcname);
>     lua_gettable(state,LUA_GLOBALSINDEX);
>     lua_pushnumber(state,pos);
>     lua_call(state,1,0);
> }
>
> static int luacv_cvCreateTrackbar(lua_State *L)
> {
>  const char *trackbar_name=luaL_checkstring(L,1);
>  const char *window_name=luaL_checkstring(L,2);
>  int value=luaL_checkint(L,3);
>  int count=luaL_checkint(L,4);
>
>  sprintf(funcname,"%s",luaL_checkstring(L,5));
>  lua_pushstring(L,funcname);
>  lua_gettable(L,LUA_GLOBALSINDEX);
>  if (lua_isfunction(L,-1))
>  {
>     sprintf(funcname,"%s",luaL_checkstring(L,-1));
>     state=lua_newthread(L);
>   }
> else
>   luaL_error(L,"luacv.cvCreateTrackbar(string trackbar_name,string
> window_name,int value,int count, name of 'void func(int pos))'");
>
> cvCreateTrackbar(trackbar_name,window_name,&value,count,mycallback);
> return 0;
> }
> ....
>
> if  state and funcname are global variables, then it works. But this
> way is limited to only one Trackbar widget per script.
>
> Unfortunately I can't use lua_State  in mycallback as you wrote with
> gpointer, because
> cvCreateTrackbar function is platform depended. Depends on GUI you
> use, including WinAPI.
>
>
> With regards,
> Jiri Prymus
>
> 2009/10/18 Francesco Abbate <francesco.bbt@gmail.com>:
>>
>> Hi,
>> I think you can do it cleanly. When you use gtk_signal_connect you
>> should pass lua_State * as a gpointer func_data. As a callback
>> function you should use a simple C function that you define in your
>> code, lets call it 'my_callback'.
>>
>> Then in my_callback you will have access the lua_State * through the
>> func_data gpointer (you need just a cast). The you need to use
>> Lua_State to put the Lua function you want in the Lua stack. The
>> function could be in the Environment, or in the registry or in the
>> global namespace of even it could already be in the stack. Then you
>> push the arguments of the Lua functions in the Lua stack and you use
>> lua_call or lua_pcall.
>>
>> Anyway, to use this schema the condition is that the GTK main event
>> loop run from a C function that was called from Lua. So the schema
>> could be:
>> - gtk_signal_connect will be used with some C functions callback that
>> you prepare on your source code. These functions will look for
>> particular Lua function and call them
>> with lua_call
>> - a Lua function is called to run the GTK main loop, some Lua
>> functions have been
>> prepared in advance in the Environment or in the Lua stack to be
>> used as callbacks
>>
>> So we can summarize the call sequence like that:
>> Lua main code => GTK main loop (C code called from Lua, a Lua stack
>> will be available) => a C callback is called by GTK main loop (we
>> still have access to the same Lua stack available for GTK main loop)
>> => a lua function is called.
>>
>> So we have closed the sequence Lua => C code => Lua.
>>
>> Of course it will be important to clean the stack before the C
>> callback terminates.
>>
>> I hope this is clear and pertinent with your problem.
>>
>> Regards,
>> Francesco
>>
>> 2009/10/17 Jiří Prymus <jiri.prymus@gmail.com>
>>>
>>> So if I understand that, I can't wrapper cvCreateTrackBar function
>>> without re-implementing it in my wrapper, because i'm not able to get
>>> proper Callback function pointer from lua and pass it to opencv
>>> library as a C function pointer.
>>>
>>> But it leads to the bypassing original library function and that isn't
>>> too great.
>>>
>>> And using hacks isn't proper for me, because it's part of my Bachelor
>>> thesis and I want clear code.
>>>
>>> Thanks for help.
>>>
>>> With regards,
>>> Jiri Prymus
>>>
>>> 2009/10/17 Wesley Smith <wesley.hoke@gmail.com>:
>>> > I've got a system that allows me to set Lua functions as callback
>>> > actions from GtkMenuItems. You can find he code here:
>>> >
>>> > // generic interface:
>>> >
>>> > http://www.mat.ucsb.edu/projects/luaAV/browser/trunk/LuaAV/library/src/LuaAVMenu.cpp
>>> > 471: int MenuItem :: action(lua_State *L)
>>> >
>>> >
>>> > // gtk callback system:
>>> >
>>> > http://www.mat.ucsb.edu/projects/luaAV/browser/trunk/LuaAV/library/linux/LuaAVMenuLinux.cpp
>>> > 93: void MenuBarImpl :: dispatch(MenuItem *mi)
>>> > 419: void MenuItem :: implEnableAction()
>>> >
>>> >
>>> > wes
>>> >
>>
>
>
>