Finding new functionality in Lua aircraft mods

[gyrovague]

Here are some tips&tricks I've developed over the past year to help figure out functionality that is available to Lua aircraft mods in DCS (but not commonly available in internet/forum searches or Beginners Guide to DCS Aircraft Modules), maybe this will help others on this path. Please share your tips&tricks too!

 

• 
   
  
• search all DCS DLLs for strings (using e.g. strings utility), especially cockpitbase.dll. This can give many false leads, but also some good ones.
  
• DLL Export Viewer on DCS DLLs, especially cockpitbase.dll. Learn to see what the Lua functions typically look like, so you can find others you didn't know about.
  
• inputenum.txt (but numerically sorted by value instead)
  
• Look at all Lua files of all other modules. Can install modules with these instructions. Can often find useful info w.r.t. gauges, switches, HUD drawing in these files, and also their default.lua files (inputs for keyb/joystick) sometimes give interesting clues (related to inputenum above). Their device_init.lua files can also give some useful info.
  
• print_message_to_user() and log.info()/log.alert() etc. functions (latter makes entries in Users/username/Saved Games/DCS/Logs/DCS.log)
  
• Dumping Lua global (_G) and metatables (see code further down)
  
• DCS modelviewer.exe in bin directory
  
• EDM arg extractor, handy together with modelviewer for figuring out how other modules do certain animation effects
  
• The Mods How To section (where this post lives) has lots of useful things, can often be found on google too though
  

 

 

Some basic common recursive table dumping code that you can include in other Lua files:

--[[
Function to recursively dump a table to a string:
Usage (e.g. to gain introspection into _G table):
str=dump("_G",_G)
local lines=strsplit("\n",str)
for k,v in ipairs(lines) do
   log.alert(v)
end
--]]
function basic_dump (o)
 if type(o) == "number" then
   return tostring(o)
 elseif type(o) == "string" then
   return string.format("%q", o)
 else -- nil, boolean, function, userdata, thread; assume it can be converted to a string
   return tostring(o)
 end
end


function dump (name, value, saved, result)
 seen = seen or {}       -- initial value
 result = result or ""
 result=result..name.." = "
 if type(value) ~= "table" then
   result=result..basic_dump(value).."\n"
 elseif type(value) == "table" then
   if seen[value] then    -- value already saved?
     result=result.."->"..seen[value].."\n"  -- use its previous name
   else
     seen[value] = name   -- save name for next time
     result=result.."{}\n"     -- create a new table
     for k,v in pairs(value) do      -- save its fields
       local fieldname = string.format("%s[%s]", name,
                                       basic_dump(k))
       if fieldname~="_G[\"seen\"]" then
         result=dump(fieldname, v, seen, result)
       end
     end
   end
 end
 return result
end

function strsplit(delimiter, text)
 local list = {}
 local pos = 1
 if string.find("", delimiter, 1) then
   return {}
 end
 while 1 do
   local first, last = string.find(text, delimiter, pos)
   if first then -- found?
     table.insert(list, string.sub(text, pos, first-1))
     pos = last+1
   else
     table.insert(list, string.sub(text, pos))
     break
   end
 end
 return list
end

 

Dumping _G with above, was able to find get_clickable_element_reference() and a bunch of other very useful

directly or indirectly.

 

Can also dump metatable of any Lua device from inside to find functions that device exposes, e.g.

local dev = GetSelf()
m=getmetatable(dev)
str=dump("GetSelf meta",m)
local lines=strsplit("\n",str)
for k,v in ipairs(lines) do
  log.alert(v)
end

 

Finding new interesting sounding function names is only half the battle, you need to often guess the parameters, that can often be quite time consuming and frustrating.

[Nero.ger]

just to make it a little easyer, in DLLs, look for functions like

 

int cockpit::avSimpleElectricSystem::l_AC_Generator_1_on(struct lua_State *) 

(its L_AC_Gen...)

 

which is callable as "GetDevice(x):AC_Generator_1_on(x)" in the Lua enviroment

 

sidenote, the complete Cockpitbase.dll dump is nearly 6000 lines ;)

[SilentEagle]

If you're interested in calling dll functions from C++, I often use dependency walker as well to see exported functions and their prototypes. As far as I know, only static functions, usually utility functions, without obscure/unique data struct parameters will be directly callable by address in this manner.

 

Another way to see exported data if you're familiar with unix systems or have cygwin installed is to use the "strings" and "grep" or "less" commands like this:

 

strings "CockpitBase.dll" | less

 

or

 

strings "CockpitBase.dll" | grep "<search_term>"

Edited February 1, 2017 by SilentEagle

[Jack McCoy]

I think

function dump (name, value, saved, result)

should be

function dump (name, value, seen, result)