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lipengzha
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检测是否为安装版引擎的方法

在 EpicGameLauncher 安装的引擎版本是不能通过 UnrealBuildTool.exe -ProjectFiles "ProgramProjectName" 来创建 TargetProgram的项目的，会提示下列错误：

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ERROR: UnrealBuildTool Exception: A game project path was not specified, which is required when generating project files using an installed build or passing -game on the command line

这个异常在 UBT 里的相关代码在ProjectFileGenreator.cs：

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// ProjectFileGenreator.cs

protected virtual void ConfigureProjectFileGeneration( String[] Arguments, ref bool IncludeAllPlatforms )
{
	// ...
	else switch(CurArgument.ToUpperInvariant() )
	{
		// ...
		case "-GAME":
			// Generates project files for a single game
			bGeneratingGameProjectFiles = true;
			break;
		// ...
	}
	// ...

	if(bGeneratingGameProjectFiles || UnrealBuildTool.IsEngineInstalled() )
	{
		if (OnlyGameProject == null)
		{
			throw new BuildException("A game project path was not specified, which is required when generating project files using an installed build or passing -game on the command line");
		}

		GameProjectName = OnlyGameProject.GetFileNameWithoutExtension();
		if (String.IsNullOrEmpty(GameProjectName))
		{
			throw new BuildException("A valid game project was not found in the specified location (" + OnlyGameProject.Directory.FullName + ")");
		}

		bool bInstalledEngineWithSource = UnrealBuildTool.IsEngineInstalled() && DirectoryReference.Exists(UnrealBuildTool.EngineSourceDirectory);

		bIncludeEngineSource = bAlwaysIncludeEngineModules || bInstalledEngineWithSource;
		bIncludeDocumentation = false;
		bIncludeBuildSystemFiles = false;
		bIncludeShaderSource = true;
		bIncludeTemplateFiles = false;
		bIncludeConfigFiles = true;
		IncludeEnginePrograms = bAlwaysIncludeEngineModules;
	}
}

可以看到，if这里如果传递给 UBT-game参数并且是引擎是安装版本 (EpicGameLauncher) 时会检测有没有传入 project 参数，如果没有就会抛异常。
正常的 UBT 调用命令：

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UnrelBuildTool.exe -ProjectFiles -project="D:\UnrealProjects\UEProject.uproject" -game

这种普通的 Game 参数在 UBT 里面是不会抛异常的。但是用生成 Program 的命令来调用 UBT，安装版引擎就会抛异常：

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UnrelBuildTool.exe -ProjectFiles ProgramName

根据上面 ProjectFileGenreator.cs 的检测代码，我们要做到的是把 UnrealBuildTool.IsEngineInstalled() 获取的结果变为 false.
继续跟代码：UnrealBuildTool.IsEngineInstalled()获得的是 UnrealBuildTool 中的一个 bool 变量bIsEngineInstalled：

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// UnrealBuildTool.cs
static public bool IsEngineInstalled()
{
	if (!bIsEngineInstalled.HasValue)
	{
		throw new BuildException("IsEngineInstalled() called before being initialized.");
	}
	return bIsEngineInstalled.Value;
}

查找引用发现在 GuardedMain 里有设置 bIsEngineInstalled 这个变量的地方：

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// UnrealBuildTool.cs
private static int GuardedMain(string[] Arguments)
{
	// ...
	try{
		// ...
		foreach (string Argument in Arguments)
		{
			string LowercaseArg = Argument.ToLowerInvariant();
			if (LowercaseArg == "-installed" || LowercaseArg == "-installedengine")
			{
				bIsEngineInstalled = true;
			}
			else if (LowercaseArg == "-notinstalledengine")
			{
				bIsEngineInstalled = false;
			}
		}
		if (!bIsEngineInstalled.HasValue)
		{
			bIsEngineInstalled = FileReference.Exists(FileReference.Combine(RootDirectory, "Engine", "Build", "InstalledBuild.txt"));
		}
		// ...
	}
}

从代码可以看到，UBT 对是不是安装版引擎的检测有三种方法：

  1. 传入参数是否有 -installled 和-installedengine
  2. 传入参数是否有-notinstallengine
  3. 判断引擎路径 Engine\Build 下是否具有 InstalledBuild.txt 文件

(说是三种其实也就是两种，就算指定了 -notinstallengine 也是要判断存不存在 Engine\Build\InstalledBuild.txt 这个文件)
而且检测的顺序是这样的:

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-installled > -installedengine > -notinstalledengine > Engine\Build\InstalledBuild.txt

所以，当我想要让 UBT 认为我的引擎版本不是安装版，有两种办法：

  1. 对 UBT 的调用传入 -notinstalledengine 参数，并且删掉 Engine\Build 目录下的 InstalledBuild.txt 文件
  2. 对 UBT 的调用不传入 -installled 和-installedengine参数，并且删掉 Engine\Build 目录下的 InstalledBuild.txt 文件

注：UBT 里还有下面两种检测：

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// UnrealBuildTools.cs
static public bool IsEnterpriseInstalled()
{
	if(!bIsEnterpriseInstalled.HasValue)
	{
		bIsEnterpriseInstalled = FileReference.Exists(FileReference.Combine(EnterpriseDirectory, "Build", "InstalledBuild.txt"));
	}
	return bIsEnterpriseInstalled.Value;
}
static public bool IsProjectInstalled()
{
	if (!bIsProjectInstalled.HasValue)
	{
		bIsProjectInstalled = FileReference.Exists(FileReference.Combine(RootDirectory, "Engine", "Build", "InstalledProjectBuild.txt"));
	}
	return bIsProjectInstalled.Value;
}