Usage of SDL_AudioSpec's callback?

[Anonymous]

Hi. Thanks for building SDLFW, it's really impressive.

As a learning project, I'm trying to translate from lft's klamrisk hero (http://www.linusakesson.net/games/klamrisk/index.php) from C/SDL to Lua/SDLFW.

I see that SDLFW_CreateAudioSpec initializes the callback parameter to SDLFW_mixaudio.

~~~~~~~~~~~~~~~~~~~~
:::::::::::C
SDL_AudioSpec APICALL SDLFW_CreateAudioSpec( void )
{
SDL_AudioSpec Spec;

Spec.freq = 0x0;
Spec.format = 0x0;
Spec.channels = 0x0;
Spec.silence = 0x0;
Spec.samples = 0x0;
Spec.padding = 0x0;
Spec.size = 0x0;
Spec.callback = SDLFW_mixaudio;
Spec.userdata = NULL;

return Spec;
}
~~~~~~~~~~~~~~~~~~~~~

And I see that in lua_SDL_AudioSpec__index, the clause dealing with callback is commented out.

~~~~~~~~~~~~~~~~~~~
::::::::::C
APIint lua_SDL_AudioSpec__index( lua_State L )
{
lua_SDL_AudioSpec ud = (lua_SDL_AudioSpec ) lua_touserdata( L, 0x1 );
if ( !strcmp(lua_tostring(L, 0x2), "freq") )
{
lua_pushnumber( L, (lua_Number) ud -> val.freq );
}
else if ( !strcmp(lua_tostring(L, 0x2), "format") )
{
lua_pushnumber( L, (lua_Number) ud -> val.format );
}
else if ( !strcmp(lua_tostring(L, 0x2), "channels") )
{
lua_pushnumber( L, (lua_Number) ud -> val.channels );
}
else if ( !strcmp(lua_tostring(L, 0x2), "silence") )
{
lua_pushnumber( L, (lua_Number) ud -> val.silence );
}
else if ( !strcmp(lua_tostring(L, 0x2), "samples") )
{
lua_pushnumber( L, (lua_Number) ud -> val.samples );
}
else if ( !strcmp(lua_tostring(L, 0x2), "padding") )
{
lua_pushnumber( L, (lua_Number) ud -> val.padding );
}
else if ( !strcmp(lua_tostring(L, 0x2), "size") )
{
lua_pushnumber( L, (lua_Number) ud -> val.size );
}
/ else if ( !strcmp(lua_tostring(L, 0x2), "callback") )
{
lua_pushlightuserdata( L, ud -> val.callback );
} */
else if ( !strcmp(lua_tostring(L, 0x2), "userdata") )
{
lua_pushlightuserdata( L, ud -> val.userdata );
};
return 0x1;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Is there an obstacle (or rather, would you please describe the obstacle) to uncommenting it, and scribbling audio buffers using lua callback functions?

[CorEduard]

SDLFW has your own internal callback (SDLFW_mixaudio) because this is more easy to implement and I don't know how to implement callbacks in Lua.

Please if do you know how to implement this callback in Lua, Can you tell me how I do to implement this feature to provide this in the new versions of SDLFW?

[Anonymous]

I'm not sure, but I think you need to use luaL_ref in that commented-out clause of ua_SDL_AudioSpec__index to make sure the lua function is not garbage collected. Then you'd have to store the int that luaL_ref returns somewhere. Then you'd have to change the ud's callback to a different C function. This new C callback would use lua_rawgeti(L, LUA_REGISTRYINDEX, <int>) to fetch the the lua callback onto the lua stack, and then call it.

http://stackoverflow.com/questions/12823934/storing-reference-to-lua-function-in-c

Sorry, I am a dilettante at lua bindings myself.

[CorEduard]

I'm sorry, I tried to implement the audio callback from Lua but no luck, maybe I get it in the future :(

Anyway I was making more testing the internal callback and worked fine and now you have too the SDL_mixer as better alternative.

So if you have any more issues, tell me please, I will try to fix them the more faster I can.