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+//========= Copyright Valve Corporation, All rights reserved. ============//
+//
+// Purpose: 
+//
+// $NoKeywords: $
+//
+//=============================================================================//
+
+// This header defines the interface convention used in the valve engine.
+// To make an interface and expose it:
+//    1. The interface must be ALL pure virtuals, and have no data members.
+//    2. Define a name for it.
+//    3. In its implementation file, use EXPOSE_INTERFACE or EXPOSE_SINGLE_INTERFACE.
+
+// Versioning
+// There are two versioning cases that are handled by this:
+// 1. You add functions to the end of an interface, so it is binary compatible with the previous interface. In this case, 
+//    you need two EXPOSE_INTERFACEs: one to expose your class as the old interface and one to expose it as the new interface.
+// 2. You update an interface so it's not compatible anymore (but you still want to be able to expose the old interface 
+//    for legacy code). In this case, you need to make a new version name for your new interface, and make a wrapper interface and 
+//    expose it for the old interface.
+
+// Static Linking:
+// Must mimic unique seperate class 'InterfaceReg' constructors per subsystem.
+// Each subsystem can then import and export interfaces as expected.
+// This is achieved through unique namespacing 'InterfaceReg' via symbol _SUBSYSTEM.
+// Static Linking also needs to generate unique symbols per interface so as to
+// provide a 'stitching' method whereby these interface symbols can be referenced
+// via the lib's primary module (usually the lib's interface exposure)
+// therby stitching all of that lib's code/data together for eventual final exe link inclusion.
+
+#ifndef INTERFACE_H
+#define INTERFACE_H
+
+#ifdef _WIN32
+#pragma once
+#endif
+
+#ifdef _LINUX
+#include <dlfcn.h> // dlopen,dlclose, et al
+#include <unistd.h>
+
+#define GetProcAddress dlsym
+
+#ifdef _snprintf
+#undef _snprintf
+#endif
+#define _snprintf snprintf
+#endif
+
+// TODO: move interface.cpp into tier0 library.
+#include "tier0/platform.h"
+
+// All interfaces derive from this.
+class IBaseInterface
+{
+public:
+	virtual	~IBaseInterface() {}
+};
+
+#if !defined( _X360 )
+#define CREATEINTERFACE_PROCNAME	"CreateInterface"
+#else
+// x360 only allows ordinal exports, .def files export "CreateInterface" at 1
+#define CREATEINTERFACE_PROCNAME	((const char*)1)
+#endif
+
+typedef void* (*CreateInterfaceFn)(const char *pName, int *pReturnCode);
+typedef void* (*InstantiateInterfaceFn)();
+
+// Used internally to register classes.
+class InterfaceReg
+{
+public:
+	InterfaceReg(InstantiateInterfaceFn fn, const char *pName);
+
+public:
+	InstantiateInterfaceFn	m_CreateFn;
+	const char				*m_pName;
+
+	InterfaceReg			*m_pNext; // For the global list.
+	static InterfaceReg		*s_pInterfaceRegs;
+};
+
+// Use this to expose an interface that can have multiple instances.
+// e.g.:
+// EXPOSE_INTERFACE( CInterfaceImp, IInterface, "MyInterface001" )
+// This will expose a class called CInterfaceImp that implements IInterface (a pure class)
+// clients can receive a pointer to this class by calling CreateInterface( "MyInterface001" )
+//
+// In practice, the shared header file defines the interface (IInterface) and version name ("MyInterface001")
+// so that each component can use these names/vtables to communicate
+//
+// A single class can support multiple interfaces through multiple inheritance
+//
+// Use this if you want to write the factory function.
+#if !defined(_STATIC_LINKED) || !defined(_SUBSYSTEM)
+#define EXPOSE_INTERFACE_FN(functionName, interfaceName, versionName) \
+	static InterfaceReg __g_Create##interfaceName##_reg(functionName, versionName);
+#else
+#define EXPOSE_INTERFACE_FN(functionName, interfaceName, versionName) \
+	namespace _SUBSYSTEM \
+	{	\
+		static InterfaceReg __g_Create##interfaceName##_reg(functionName, versionName); \
+	}
+#endif
+
+#if !defined(_STATIC_LINKED) || !defined(_SUBSYSTEM)
+#define EXPOSE_INTERFACE(className, interfaceName, versionName) \
+	static void* __Create##className##_interface() {return static_cast<interfaceName *>( new className );} \
+	static InterfaceReg __g_Create##className##_reg(__Create##className##_interface, versionName );
+#else
+#define EXPOSE_INTERFACE(className, interfaceName, versionName) \
+	namespace _SUBSYSTEM \
+	{	\
+		static void* __Create##className##_interface() {return static_cast<interfaceName *>( new className );} \
+		static InterfaceReg __g_Create##className##_reg(__Create##className##_interface, versionName ); \
+	}
+#endif
+
+// Use this to expose a singleton interface with a global variable you've created.
+#if !defined(_STATIC_LINKED) || !defined(_SUBSYSTEM)
+#define EXPOSE_SINGLE_INTERFACE_GLOBALVAR_WITH_NAMESPACE(className, interfaceNamespace, interfaceName, versionName, globalVarName) \
+	static void* __Create##className##interfaceName##_interface() {return static_cast<interfaceNamespace interfaceName *>( &globalVarName );} \
+	static InterfaceReg __g_Create##className##interfaceName##_reg(__Create##className##interfaceName##_interface, versionName);
+#else
+#define EXPOSE_SINGLE_INTERFACE_GLOBALVAR_WITH_NAMESPACE(className, interfaceNamespace, interfaceName, versionName, globalVarName) \
+	namespace _SUBSYSTEM \
+	{ \
+		static void* __Create##className##interfaceName##_interface() {return static_cast<interfaceNamespace interfaceName *>( &globalVarName );} \
+		static InterfaceReg __g_Create##className##interfaceName##_reg(__Create##className##interfaceName##_interface, versionName); \
+	}
+#endif
+
+#define EXPOSE_SINGLE_INTERFACE_GLOBALVAR(className, interfaceName, versionName, globalVarName) \
+	EXPOSE_SINGLE_INTERFACE_GLOBALVAR_WITH_NAMESPACE(className, , interfaceName, versionName, globalVarName)
+
+// Use this to expose a singleton interface. This creates the global variable for you automatically.
+#if !defined(_STATIC_LINKED) || !defined(_SUBSYSTEM)
+#define EXPOSE_SINGLE_INTERFACE(className, interfaceName, versionName) \
+	static className __g_##className##_singleton; \
+	EXPOSE_SINGLE_INTERFACE_GLOBALVAR(className, interfaceName, versionName, __g_##className##_singleton)
+#else
+#define EXPOSE_SINGLE_INTERFACE(className, interfaceName, versionName) \
+	namespace _SUBSYSTEM \
+	{	\
+		static className __g_##className##_singleton; \
+	}	\
+	EXPOSE_SINGLE_INTERFACE_GLOBALVAR(className, interfaceName, versionName, __g_##className##_singleton)
+#endif
+
+// load/unload components
+class CSysModule;
+
+// interface return status
+enum 
+{
+	IFACE_OK = 0,
+	IFACE_FAILED
+};
+
+//-----------------------------------------------------------------------------
+// This function is automatically exported and allows you to access any interfaces exposed with the above macros.
+// if pReturnCode is set, it will return one of the following values (IFACE_OK, IFACE_FAILED)
+// extend this for other error conditions/code
+//-----------------------------------------------------------------------------
+DLL_EXPORT void* CreateInterface(const char *pName, int *pReturnCode);
+
+#if defined( _X360 )
+DLL_EXPORT void *CreateInterfaceThunk( const char *pName, int *pReturnCode );
+#endif
+
+//-----------------------------------------------------------------------------
+// UNDONE: This is obsolete, use the module load/unload/get instead!!!
+//-----------------------------------------------------------------------------
+extern CreateInterfaceFn	Sys_GetFactory( CSysModule *pModule );
+extern CreateInterfaceFn	Sys_GetFactory( const char *pModuleName );
+extern CreateInterfaceFn	Sys_GetFactoryThis( void );
+
+enum Sys_Flags
+{
+    SYS_NOFLAGS = 0x00,
+    SYS_NOLOAD = 0x01   // no loading, no ref-counting, only returns handle if lib is loaded. 
+};
+
+//-----------------------------------------------------------------------------
+// Load & Unload should be called in exactly one place for each module
+// The factory for that module should be passed on to dependent components for
+// proper versioning.
+//-----------------------------------------------------------------------------
+extern CSysModule			*Sys_LoadModule( const char *pModuleName, Sys_Flags flags = SYS_NOFLAGS );
+extern void					Sys_UnloadModule( CSysModule *pModule );
+
+// This is a helper function to load a module, get its factory, and get a specific interface.
+// You are expected to free all of these things.
+// Returns false and cleans up if any of the steps fail.
+bool Sys_LoadInterface(
+	const char *pModuleName,
+	const char *pInterfaceVersionName,
+	CSysModule **pOutModule,
+	void **pOutInterface );
+
+bool Sys_IsDebuggerPresent();
+
+//-----------------------------------------------------------------------------
+// Purpose: Place this as a singleton at module scope (e.g.) and use it to get the factory from the specified module name.  
+// 
+// When the singleton goes out of scope (.dll unload if at module scope),
+//  then it'll call Sys_UnloadModule on the module so that the refcount is decremented 
+//  and the .dll actually can unload from memory.
+//-----------------------------------------------------------------------------
+class CDllDemandLoader
+{
+public:
+						CDllDemandLoader( char const *pchModuleName );
+	virtual				~CDllDemandLoader();
+	CreateInterfaceFn	GetFactory();
+	void				Unload();
+
+private:
+
+	char const	*m_pchModuleName;
+	CSysModule	*m_hModule;
+	bool		m_bLoadAttempted;
+};
+
+#endif
+
+
+