小冰狼

本文涉及UE4引擎打开项目时，如何选择本地多个引擎目录并判断是否对项目编译的原理介绍

原理

uproject

项目文件通过t的EngineAssociation属性与引擎Appname比较判断项目是否是使用当前引擎

流程

WinMain
Main
UnrealVersionSelector 入口
SwitchVersion
版本选择入口

FWindowsPlatformInstallation::SelectEngineInstallation
弹出select对话框

bool FWindowsPlatformInstallation::SelectEngineInstallation(FString &amp;Identifier)
{
   FSelectBuildDialog Dialog(Identifier);
   if(!Dialog.DoModal(NULL))
   {
      return false;
   }

   Identifier = Dialog.Identifier;
   return true;
}

FDesktopPlatformWindows::EnumerateEngineInstallations

读取Launch的引擎路径
读取Innov配置的引擎路径
读取注册表中的注册的引擎路径

三类引擎的路径都存入OutInstallations

void FDesktopPlatformWindows::EnumerateEngineInstallations(TMap<FString, FString> &amp;OutInstallations)
{
   // Enumerate the binary installations
   EnumerateLauncherEngineInstallations(OutInstallations);
   
   EnumerateInnovEngineInstallations(OutInstallations);
   // Enumerate the per-user installations
   HKEY hKey;
   if (RegOpenKeyEx(HKEY_CURRENT_USER, InstallationsSubKey, 0, KEY_ALL_ACCESS, &amp;hKey) == ERROR_SUCCESS)
   {
      // Get a list of all the directories
      TArray<FString> UniqueDirectories;
      OutInstallations.GenerateValueArray(UniqueDirectories);

      // Enumerate all the installations
      TArray<FString> InvalidKeys;
      for (::DWORD Index = 0;; Index++)
      {
         TCHAR ValueName[256];
         TCHAR ValueData[MAX_PATH];
         ::DWORD ValueType = 0;
         ::DWORD ValueNameLength = sizeof(ValueName) / sizeof(ValueName[0]);
         ::DWORD ValueDataSize = sizeof(ValueData);

         LRESULT Result = RegEnumValue(hKey, Index, ValueName, &amp;ValueNameLength, NULL, &amp;ValueType, (BYTE*)&amp;ValueData[0], &amp;ValueDataSize);
         if(Result == ERROR_SUCCESS)
         {
            int32 ValueDataLength = ValueDataSize / sizeof(TCHAR);
            if(ValueDataLength > 0 &amp;&amp; ValueData[ValueDataLength - 1] == 0) ValueDataLength--;

            FString NormalizedInstalledDirectory(ValueDataLength, ValueData);
            FPaths::NormalizeDirectoryName(NormalizedInstalledDirectory);
            FPaths::CollapseRelativeDirectories(NormalizedInstalledDirectory);

            if(IsValidRootDirectory(NormalizedInstalledDirectory) &amp;&amp; !UniqueDirectories.Contains(NormalizedInstalledDirectory))
            {
               OutInstallations.Add(ValueName, NormalizedInstalledDirectory);
               UniqueDirectories.Add(NormalizedInstalledDirectory);
            }
            else
            {
               InvalidKeys.Add(ValueName);
            }
         }
         else if(Result == ERROR_NO_MORE_ITEMS)
         {
            break;
         }
      }

      // Remove all the keys which weren't valid
      for(const FString InvalidKey: InvalidKeys)
      {
         RegDeleteValue(hKey, *InvalidKey);
      }

      RegCloseKey(hKey);
   }
}

FDesktopPlatformBase::EnumerateInnovEngineInstallations

读取InnovInstall 路径

存入OutInstallations

void FDesktopPlatformBase::EnumerateInnovEngineInstallations(TMap<FString, FString> &amp;OutInstallations)
{
   //see:FDesktopPlatformBase::EnumerateLauncherEngineInstallations
   // Cache the Innov install list if necessary
   //1. 读取InnovInstall 路径
   ReadInnovInstallationList();
   
   for(TMap<FString, FString>::TConstIterator Iter(InnovInstallationList); Iter; ++Iter)
   {
      FString AppName = Iter.Key();
      //2. 存入OutInstallations
      OutInstallations.Add(AppName, Iter.Value());
   }
}

FDesktopPlatformBase：：ReadInnovInstallationList()

从 RootDirectory / TEXT(“Engine/Build/InnovInstalled.dat”) InnovInstallEngine路径

将读取到的InnovInstallEngine路径存入InnovInstallationList

//引擎根路径
const FString RootDirectory = FPaths::RootDir();
//1. 从 RootDirectory / TEXT("Engine/Build/InnovInstalled.dat")  InnovInstallEngine路径
const FString InstalledListFile = RootDirectory / TEXT("Engine/Build/InnovInstalled.dat");

// Read the installation manifest
FString InstalledText;
if (FFileHelper::LoadFileToString(InstalledText, *InstalledListFile))
{
   // Deserialize the object
   TSharedPtr< FJsonObject > RootObject;
   const TSharedRef< TJsonReader<> > Reader = TJsonReaderFactory<>::Create(InstalledText);
   if (FJsonSerializer::Deserialize(Reader, RootObject) &amp;&amp; RootObject.IsValid())
   {
      // Parse the list of installations
      TArray< TSharedPtr<FJsonValue> > InstallationList = RootObject->GetArrayField(TEXT("InstallationList"));
      for(int32 Idx = 0; Idx < InstallationList.Num(); Idx++)
      {
         const TSharedPtr<FJsonObject> InstallationItem = InstallationList[Idx]->AsObject();

         FString AppName = InstallationItem->GetStringField(TEXT("AppName"));
         //使用当前引擎作为Innov引擎
         FString InstallLocation = RootDirectory;
         if(AppName.Len() > 0 &amp;&amp; InstallLocation.Len() > 0)
         {
            FPaths::NormalizeDirectoryName(InstallLocation);
            // 2. 将读取到的InnovInstallEngine路径存入InnovInstallationList
            InnovInstallationList.Add(AppName, InstallLocation);
         }
      }
   }
}

DesktopPlatformWindows.cpp

引擎默认是使用Install目录的UnrealVersionSelector.exe, 将注册的UnrealVersionSelector的路径改为当前目录的路基

// Defer to UnrealVersionSelector.exe in a launcher installation if it's got the same version number or greater.
// FString InstallDir;
// if (FWindowsPlatformMisc::QueryRegKey(HKEY_LOCAL_MACHINE, TEXT("SOFTWARE\\EpicGames\\Unreal Engine"), TEXT("INSTALLDIR"), InstallDir) && (InstallDir.Len() > 0))
// {
	// FString NormalizedInstallDir = InstallDir;
	// FPaths::NormalizeDirectoryName(NormalizedInstallDir);

	// FString InstalledExecutableFileName = NormalizedInstallDir / FString("Launcher/Engine/Binaries/Win64/UnrealVersionSelector.exe");
	// if(GetShellIntegrationVersion(InstalledExecutableFileName) == GetShellIntegrationVersion(ExecutableFileName))
	// {
	// 	ExecutableFileName = InstalledExecutableFileName;
	// }
// }

//change UnrealVersionSelector.exe in a launcher installation to UnrealVersionSelector.exe in InnovUE4 installation
FString InstalledExecutableFileName = ExecutableFileName;

使用

在Programs下找到UnrealVersionSelector项目进行编译
查看Engine\Binaries\Win64是否存在UnrealVersionSelector.exe，不是UnrealVersionSelector-Win64-Shipping
1. UnrealVersionSelector-Win64-Shipping 使用的是UE4 install 版本的程序
2. 我们需要使用我们改过多那个版本
我们编译的UnrealVersionSelector.exe生成后，双击即可将其注册为默认UnrealVersionSelector,(也可以使用 RegisterUnrealVersionSelector.bat 注册当前引擎版本的UnrealVersionSelector，之后就可以直接打开uproject)
查看注册表计算机\HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Unreal.ProjectFile\DefaultIcon，是否已经是自己引擎中UnrealVersionSelector.exe

构建
构建Install版本时，需要执行Engine\Build\Graph\Innov\AddVersionSelectorToInstall.xml 将UnrealVersionSelector复制到binary中
InnovUE4版本名称在 Engine\Build\InnovInstalled.dat 中配置

总结

UnrealVersionSelector 用于打开项目前的引擎选择，还有其他可能可以继续改进或添加新的特性

原理

uproject

流程

使用

构建

总结