Hello, I'm attempting to interface with the Steam API DLL in D
and running into some trouble working with callbacks. I'm aware
there's already a project here http://derelict-steamworks.dub.pm/
but it seems to have not yet addressed the same issue. Steam
provides ways to poll for whether an asynchronous request has
completed yet and retrieve the results, but what I am trying to
implement is receiving actual callbacks from the API.
Just for reference, I've gotten simple callbacks working in other
APIs (passing a D function pointer to a C function and having it
be called back), and the other basic Steam functions that don't
deal with callbacks all work fine (defined in D as extern(C)).
Here's where I'm running into trouble:
Definitions in C++ headers provided by Steam:
typedef uint64 SteamAPICall_t;
S_API void S_CALLTYPE SteamAPI_RegisterCallResult( class
CCallbackBase *pCallback, SteamAPICall_t hAPICall );
S_API void S_CALLTYPE SteamAPI_UnregisterCallResult( class
CCallbackBase *pCallback, SteamAPICall_t hAPICall );
class CCallbackBase
{
public:
CCallbackBase() { m_nCallbackFlags = 0; m_iCallback = 0; }
// don't add a virtual destructor because we export this binary
interface across dll's
virtual void Run( void *pvParam ) = 0;
virtual void Run( void *pvParam, bool bIOFailure, SteamAPICall_t
hSteamAPICall ) = 0;
int GetICallback() { return m_iCallback; }
virtual int GetCallbackSizeBytes() = 0;
protected:
enum { k_ECallbackFlagsRegistered = 0x01,
k_ECallbackFlagsGameServer = 0x02 };
uint8 m_nCallbackFlags;
int m_iCallback;
friend class CCallbackMgr;
private:
CCallbackBase( const CCallbackBase& );
CCallbackBase& operator=( const CCallbackBase& );
};
It's actually more complex than that as it has templated classes
that inherit from that base so that there is a different template
for each expected struct that gets returned from various async
requests. I'm trying to get the simplest possible scenario
working first and hoping I'm not missing anything, but I don't
actually understand how I'm supposed to work with the C++ objects
enough really to be sure. Here's how I've defined it in D, as
per https://dlang.org/spec/cpp_interface.html#classes :
alias ulong SteamAPICall_t;
extern(C) {
void SteamAPI_RegisterCallResult(CCallbackBase pCallback,
SteamAPICall_t hAPICall);
void SteamAPI_UnregisterCallResult(CCallbackBase pCallback,
SteamAPICall_t hAPICall);
}
extern(C++) {
interface CCallbackBase {
//this() { m_nCallbackFlags = 0; m_iCallback = 0; }
void Run( void *pvParam );
void Run( void *pvParam, bool bIOFailure, SteamAPICall_t
hSteamAPICall );
int GetICallback();
int GetCallbackSizeBytes();
enum { k_ECallbackFlagsRegistered = 0x01,
k_ECallbackFlagsGameServer = 0x02 }
//uint8 m_nCallbackFlags;
//int m_iCallback;
//friend class CCallbackMgr;
//CCallbackBase( const CCallbackBase& );
//CCallbackBase& operator=( const CCallbackBase& );
}
}
class CImpl : CCallbackBase {
extern(C++) {
this() { m_nCallbackFlags = 0; m_iCallback = 0; }
void Run( void *pvParam ) { writeln("Run1"); }
void Run( void *pvParam, bool bIOFailure, SteamAPICall_t
hSteamAPICall ) { writeln("Run2"); }
int GetICallback() { return m_iCallback; }
int GetCallbackSizeBytes() { return
NumberOfCurrentPlayers_t.sizeof; } // ordinarily use templates to
determine what type struct ptr to return
}
uint8 m_nCallbackFlags;
int m_iCallback;
}
Which then gets called later on as:
auto cbk = new CImpl();
cbk.m_iCallback = NumberOfCurrentPlayers_t.k_iCallback;
auto hid =
SteamAPI_ISteamUserStats_GetNumberOfCurrentPlayers(...);
SteamAPI_RegisterCallResult(cbk, hid);
And then every frame SteamAPI_RunCallbacks(); runs, which is
supposed to fire off the callbacks. I've also tried using
abstract class instead of interface. My expectation of what's
supposed to happen is that one of those Run() functions gets
called at some point. However, it never does (even though I can
poll to determine the call has actually completed). I'm hoping
the problem is I'm simply not passing the right expected type of
data to the registration function and/or haven't defined the
interface in D properly (I admit I have very little idea how the
C++ is working anymore, including what those private methods are
for), and not an issue with utilizing the API itself, since I
doubt there's anyone I could ask on the Steam end of things about
interfacing with D.
My gut feeling is I'm doing something very incorrect/stupid on
the definition end of things, I understand passing function
pointers to C++ functions that intend to call back well enough
but I'm confused about this concept of passing "class SomeClass
*" to a function and expecting it to call a method on that class,
I don't know where everything is supposed to "exist". If anyone
has any insight to provide it would be greatly appreciated,
thanks!
