首页 游戏引擎 UE

[toc]

# 序

学习 UE5 的渲染。

# Shader 加载流

# 读取虚拟着色期目录

在 UE 引擎对一系列的 args 处理完毕后，会有一个阶段进入 Shader 的加载流程

LaunchEngineLoop.cpp

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#if WITH_ENGINE
    // Add the default engine shader dir
    AddShaderSourceDirectoryMapping(TEXT("/Engine"), FPlatformProcess::ShaderDir());
#endif
  1. 检查是否在主线程
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check(IsInGameThread());
  1. 如果使用 CookData 或者不允许 Shader 编译，就结束流程
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if (FPlatformProperties::RequiresCookedData()  !AllowShaderCompiling())
{
    return;
}
  1. 源码版本的 Shader 在 EngineShaders 目录下 (Combind Engine Dir/Shaders/)

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const TCHAR* FGenericPlatformProcess::ShaderDir()
{
    if (Generic_ShaderDir.Len() == 0)
    {
        Generic_ShaderDir = FPaths::Combine(*(FPaths::EngineDir()), TEXT("Shaders"));
    }
    return *Generic_ShaderDir;
}
  1. 将着色器目录添加到全局 Mapping 中 (虚拟着色器 -> 真实着色器映射)
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GShaderSourceDirectoryMappings.Add(VirtualShaderDirectory, RealShaderDirectory);
  1. 自动着色器目录 [项目名]IntermediateShaderAutogen , 同样也会被添加到虚拟着色器映射中
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#if WITH_EDITOR
    {
        IPlatformFile& PlatformFile = FPlatformFileManager::Get().GetPlatformFile();
        FString ProjectIntermediateDir = FPaths::ProjectIntermediateDir();
        bool bCreateIntermediateSuccess = PlatformFile.CreateDirectoryTree(*ProjectIntermediateDir);
        if (!bCreateIntermediateSuccess)
        {
            UE_LOG(LogInit, Fatal, TEXT("Failed to create Intermediate directory '%s'."), *ProjectIntermediateDir);
        }

        FString AutogenAbsolutePath = FPaths::ConvertRelativePathToFull(ProjectIntermediateDir / TEXT("ShaderAutogen"));
        bool bCreateAutogenSuccess = PlatformFile.CreateDirectory(*AutogenAbsolutePath);
        if (!bCreateAutogenSuccess)
        {
            UE_LOG(LogInit, Fatal, TEXT("Failed to create Intermediate/ShaderAutogen/ directory '%s'. Make sure Intermediate exists."), *AutogenAbsolutePath);
        }

        AddShaderSourceDirectoryMapping(TEXT("/ShaderAutogen"), AutogenAbsolutePath);
    }
#endif //WITH_EDITOR
  1. 加载初始化模块
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{
    SCOPED_BOOT_TIMING("LoadPreInitModules");
    LoadPreInitModules();
}

//内部实现 

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();

#if !UE_SERVER
    if (!IsRunningDedicatedServer() )
    {
        if (!GUsingNullRHI)
        {
            // This needs to be loaded before InitializeShaderTypes is called
            FModuleManager::Get().LoadModuleChecked<ISlateRHIRendererModule>("SlateRHIRenderer");
        }
    }
#endif

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

    // Initialize ShaderCore before loading or compiling any shaders,
    // But after Renderer and any other modules which implement shader types.
    FModuleManager::Get().LoadModule(TEXT("RenderCore"));

#if WITH_EDITORONLY_DATA
    // Load the texture compressor module before any textures load. They may
    // compress asynchronously and that can lead to a race condition.
    FModuleManager::Get().LoadModule(TEXT("TextureCompressor"));
#endif

    if (!FPlatformProperties::RequiresCookedData())
    {
        FModuleManager::Get().LoadModule(TEXT("Virtualization"));
    }
#endif // WITH_ENGINE

#if WITH_EDITOR
    // Load audio editor module before engine class CDOs are loaded
    FModuleManager::Get().LoadModule(TEXT("AudioEditor"));

#if !(UE_BUILD_SHIPPING  UE_BUILD_TEST) // todo: revist
    FModuleManager::Get().LoadModule(TEXT("AnimationModifiers"));
#endif // !(UE_BUILD_SHIPPING  UE_BUILD_TEST)
#endif // WITH_EDITOR
}


可以发现，在这一部分，加载了大部分需要的模块，最终对于每一个模块返回的是一个指向模块的指针

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FORCEINLINE T* Get() const
{
    return Ptr;
}

# 代理

UE 理有很多代理，是用来掌控生命周期的，类似于 Unity 的 Update 之类的方法，有生命周期自行调用，其他模块进行注册 其中核心大部分代理都放在 FCoreDelegates 中 举几个最常见的例子:

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// Called at the beginning of a frame
static FSimpleMulticastDelegate OnBeginFrame;

// Called at the moment of sampling the input (currently on the gamethread)
static FSimpleMulticastDelegate OnSamplingInput;

// Called at the end of a frame
static FSimpleMulticastDelegate OnEndFrame;

// Called at the beginning of a frame on the renderthread
static FSimpleMulticastDelegate OnBeginFrameRT;

// Called at the end of a frame on the renderthread
static FSimpleMulticastDelegate OnEndFrameRT;

只需要在合适的地方调用 Delegate.AddStatic(方法) 即可