Designing Games with Game Maker - YoYo Games

StrCat(res,str);
end;
Result := res;
exports MyMin, DoubleString;
begin
end.
This DLL defines two functions: MyMin that takes two real arguments and returns the
minimum of the two, and DoubleString that doubles the string. Note that you have to be
careful with memory management. That is why I declared the resulting string global. Also
notice the use of the cdecl calling convention. You can either use cdecl or stdcall calling
conventions. Once you build the DLL in Delphi you will get a file MyDLL.DLL. This file must be
placed in the running directory of your game. (Or any other place where Windows can find it.)
To use this DLL in Game Maker you first need to specify the external functions you want to use
and what type of arguments they take. For this there is the following function in GML:
external_define(dll,name,calltype,restype,argnumb,arg1type,
arg2type, ...) Defines an external function. dll is the name of the dll file.
name is the name of the functions. calltype is the calling convention used. For
this use either dll_cdecl or dll_stdcall. restype is the type of the result. For this
use either ty_real or ty_string. argnumb is the number of arguments (0-16).
Next, for each argument you must specify its type. For this again use either
ty_real or ty_string. When there are more than 4 arguments all of them must
be of type ty_real.
This function returns the id of the external function that must be used for calling it. So in the
above example, at the start of the game you would use the following GML code:
{
global.mmm =
external_define('MyDLL.DLL','MyMin',dll_cdecl,