Why do not enable Nanite Imposter by default

Development Rendering
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Hi Everyone. I am currently using UE 5.2 precompiled version from epic games launcher. I noticed that the ‘r.Nanite.Builder.Imposters’ cvar did not show up because there is a C++ macro NANITE_IMPOSTERS_SUPPORTED was defined to 0 which means I could not use the imposter functionality when Nanite instances become tiny instances. So why disable Nanite Imposters and how can I use them? Many thanks :smile: !!!

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I’m bumping this thread because I’ve just discovered Nanite impostors and noticed that the feature is disabled by default. In NaniteDefinitions.h, the flag NANITE_IMPOSTERS_SUPPORTED is hard-coded to 0, which effectively prevents us from using impostor generation in our project since we’re not building from the open-source engine. Has anyone figured out a way to enable Nanite impostors without rebuilding the entire engine from source?

EDIT1: Five minutes - and one existential crisis - later, I discovered I can actually flip the switch in my .Build.cs, like this:

public class MyGame : ModuleRules
{
	public MyGame(ReadOnlyTargetRules Target) : base(Target)
	{
		PCHUsage = PCHUsageMode.UseExplicitOrSharedPCHs;
		
		PublicDefinitions.Add("NANITE_IMPOSTERS_SUPPORTED=1");
	
		PublicDependencyModuleNames.AddRange(new string[] 
		{ 
			"Core",
			...

It should work after rebuilding the project.

EDIT2: Next, let’s enable the console variable r.Nanite.Builder.Imposters, which is declared (when NANITE_IMPOSTERS_SUPPORTED is true) in NaniteBuilder.cpp like this:

#if NANITE_IMPOSTERS_SUPPORTED
static TAutoConsoleVariable<bool> CVarBuildImposters(
    TEXT("r.Nanite.Builder.Imposters"),
    false,
    TEXT("Build imposters for small or distant objects. "
         "Imposters can improve performance in scenes with many small or faraway meshes, "
         "at the cost of additional memory and disk usage."),
    ECVF_ReadOnly
);
#endif

By default this variable is set to false. And it is ECVF_ReadOnly so it needs to be set via .ini file. So I attempted to override it in DefaultEngine.ini:

[/Script/Engine.RendererSettings]
r.Nanite.Builder.Imposters=1

On startup, however, the log reports:

LogConfig: CVar [[r.Nanite.Builder.Imposters:1]] deferred – dummy variable created

This indicates the console variable isn’t being registered, which suggests NANITE_IMPOSTERS_SUPPORTED remains disabled at compile time. There’s still a missing piece to make this take effect.

EDIT3: Surprisingly, a simple check in my code reports that imposters are enabled:

#if NANITE_IMPOSTERS_SUPPORTED
    UE_LOG(LogTemp, Warning, TEXT("Nanite Imposters are supported!"));
#else
    UE_LOG(LogTemp, Warning, TEXT("Nanite Imposters are NOT supported"));
#endif

And the output is: LogTemp: Warning: Nanite Imposters are supported!. This confirms the define is active, even though the console variable never registers at runtime.

EDIT4: I tried setting the define in editor module’s Build.cs instead of game one, and pulling in the NaniteBuilder module:

public class MyEditorModule : ModuleRules
{
    public MyEditorModule(ReadOnlyTargetRules Target) : base(Target)
    {
        ...

        PublicDefinitions.Add("NANITE_IMPOSTERS_SUPPORTED=1");

        PublicDependencyModuleNames.AddRange(new string[]
        {
            "NaniteBuilder"
        });

        ...

No dice - the console variable still never registers. At this point I’m pretty sure I have to edit the #define NANITE_IMPOSTERS_SUPPORTED 0 in the engine’s source directly. I’ll spin up a fresh source-based project soon, patch that line, and report back on whether it finally activates the feature.

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