跟着

https://www.cnblogs.com/timlly/p/13877623.html

学习

入口函数

UnrealEngine\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp

WinMain 入口

int32 WINAPI WinMain(_In_ HINSTANCE hInInstance, _In_opt_ HINSTANCE hPrevInstance, _In_ char* pCmdLine, _In_ int32 nCmdShow)
{
	int32 Result = LaunchWindowsStartup(hInInstance, hPrevInstance, pCmdLine, nCmdShow, nullptr);
	LaunchWindowsShutdown();
	return Result;
}

然后进入 LAUNCH_API int32 LaunchWindowsStartup( HINSTANCE hInInstance, HINSTANCE hPrevInstance, char*, int32 nCmdShow, const TCHAR* CmdLine )

似乎是经过一些 debugger

然后进入 GuardedMain

UnrealEngine\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp

	// When we're running embedded, assume that the outer application is going to be handling crash reporting
#if UE_BUILD_DEBUG
	if (GUELibraryOverrideSettings.bIsEmbedded || !GAlwaysReportCrash)
#else
	if (GUELibraryOverrideSettings.bIsEmbedded || bNoExceptionHandler || (bIsDebuggerPresent && !GAlwaysReportCrash))
#endif
	{
		// Don't use exception handling when a debugger is attached to exactly trap the crash. This does NOT check
		// whether we are the first instance or not!
		ErrorLevel = GuardedMain( CmdLine );
	}

预初始化

然后就进入 EnginePreInit

UnrealEngine\Engine\Source\Runtime\Launch\Private\Launch.cpp

	int32 ErrorLevel = EnginePreInit( CmdLine );

然后是

UnrealEngine\Engine\Source\Runtime\Launch\Private\Launch.cpp

/** 
 * PreInits the engine loop 
 */
int32 EnginePreInit( const TCHAR* CmdLine )
{
	int32 ErrorLevel = GEngineLoop.PreInit( CmdLine );

	return( ErrorLevel );
}

然后是

UnrealEngine\Engine\Source\Runtime\Launch\Private\LaunchEngineLoop.cpp

int32 FEngineLoop::PreInit(const TCHAR* CmdLine)
{
#if UE_ENABLE_ARRAY_SLACK_TRACKING
	// Any array allocations before this point won't have array slack tracking, although subsequent reallocations of existing arrays
	// will gain tracking if that occurs.  The goal is to filter out startup constructors which run before Main, which introduce a
	// ton of noise into slack reports.  Especially the roughly 30,000 static FString constructors in the code base, each with a
	// unique call stack, and all having a little bit of slack due to malloc bucket size rounding.
	ArraySlackTrackInit();
#endif

	const int32 rv1 = PreInitPreStartupScreen(CmdLine);
	if (rv1 != 0)
	{
		PreInitContext.Cleanup();
		return rv1;
	}

	const int32 rv2 = PreInitPostStartupScreen(CmdLine);
	if (rv2 != 0)
	{
		PreInitContext.Cleanup();
		return rv2;
	}

	return 0;
}

然后跳到了 int32 FEngineLoop::PreInitPreStartupScreen(const TCHAR* CmdLine)

不断步进，然后看到一个问题

#if WITH_ENGINE
	// Add the default engine shader dir
	AddShaderSourceDirectoryMapping(TEXT("/Engine"), FPlatformProcess::ShaderDir());

UnrealEngine\Engine\Source\Runtime\RenderCore\Private\ShaderCore.cpp

前面大部分都是在检查

void AddShaderSourceDirectoryMapping(const FString& VirtualShaderDirectory, const FString& RealShaderDirectory)
{
	...
	
	GShaderSourceDirectoryMappings.Add(VirtualShaderDirectory, RealShaderDirectory);
}

最终也只是把它放到一个 map 里面

UnrealEngine\Engine\Source\Runtime\RenderCore\Private\ShaderCore.cpp

/** Global map of virtual file path to physical file paths */
static TMap<FString, FString> GShaderSourceDirectoryMappings;

然后后面还有调用 AddShaderSourceDirectoryMapping 的

然后是加载 module

UnrealEngine\Engine\Source\Runtime\Launch\Private\LaunchEngineLoop.cpp

	// Load Core modules required for everything else to work (needs to be loaded before InitializeRenderingCVarsCaching)
	{
		SCOPED_BOOT_TIMING("LoadCoreModules");
		if (!LoadCoreModules())
		{
			UE_LOG(LogInit, Error, TEXT("Failed to load Core modules."));
			return 1;
		}
	}

	...

	{
		SCOPED_BOOT_TIMING("LoadPreInitModules");
		LoadPreInitModules();
	}

加载 module 都是用的 FModuleManager::Get().LoadModule

UnrealEngine\Engine\Source\Runtime\Launch\Private\LaunchEngineLoop.cpp

部分代码

void FEngineLoop::LoadPreInitModules()
{
	DECLARE_SCOPE_CYCLE_COUNTER(TEXT("Loading PreInit Modules"), STAT_PreInitModules, STATGROUP_LoadTime);

	// GGetMapNameDelegate is initialized here
#if WITH_ENGINE
	FModuleManager::Get().LoadModule(TEXT("Engine"));

	FModuleManager::Get().LoadModule(TEXT("Renderer"));

	FModuleManager::Get().LoadModule(TEXT("AnimGraphRuntime"));

	FPlatformApplicationMisc::LoadPreInitModules();

之后似乎我也看不懂

于是回到 int32 FEngineLoop::PreInit(const TCHAR* CmdLine)

奇怪的是，我在 const int32 rv2 = PreInitPostStartupScreen(CmdLine); 这里加了断点，但是直到选择项目的界面出现了，也没有触发

但是毫无疑问，我从 int32 ErrorLevel = EnginePreInit( CmdLine ); 里面退出来之后，接下来还是继续留在 int32 GuardedMain( const TCHAR* CmdLine ) 里面，并且这个时候也没进到项目选择的界面

所以……那个问题就不管了

然后是编辑器初始化

UnrealEngine\Engine\Source\Runtime\Launch\Private\Launch.cpp

#if WITH_EDITOR
		if (GIsEditor)
		{
			ErrorLevel = EditorInit(GEngineLoop);
		}
		else
#endif
		{
			ErrorLevel = EngineInit();
		}
	}

初始化这里似乎不应该深究

我看 UE 官方的 PPT 都说很多人讨厌臃肿的初始化hhh