Compile-Time Switches

Five VITE_* macros in Engine/Source/Runtime/Core/Public/Misc/CoreDefines.h control features that are decided at compile time rather than by console variable. VITE_RT_PSO_DEBLOAT defaults to 1 and compiles out several ray tracing effects entirely — read that section before concluding a feature is broken.

Some Vite features cannot be console variables. Either they change shader permutation sets, which are decided when shaders are compiled, or they alter hot code paths where a runtime branch would cost more than the feature saves.

The switches

Each is defined with an #ifndef guard, so any of them can be overridden from the build system without editing the header.

Overriding a switch

Open your project's Source/<Project>.Target.cs, or the engine target file if you are changing it engine-wide. Add the definition to GlobalDefinitions: public MyGameTarget(TargetInfo Target) : base(Target) { Type = TargetType.Game; DefaultBuildSettings = BuildSettingsVersion.V2; ExtraModuleNames.Add("MyGame");

GlobalDefinitions.Add("VITE_RT_PSO_DEBLOAT=0");

} Regenerate project files. Rebuild the engine, and wipe the shader cache if you changed VITE_RT_PSO_DEBLOAT or any switch that affects shader permutations. See Cache Management.

Prefer GlobalDefinitions in a target file over editing CoreDefines.h. Editing the header changes the value for every target and creates a diff against the engine repository that you will have to carry through every merge.

VITE_RT_PSO_DEBLOAT

This is the switch that surprises people, so it gets the most detail.

Ray tracing pipeline state objects are expensive in a way that is easy to miss. Every ray generation shader permutation that could be used has to be compiled, packaged and bound into the ray tracing pipeline, even if the effect it belongs to is disabled at runtime by a console variable. A CVar set to 0 does not stop its shaders existing. The result is long shader compile times, large packaged builds, high PSO counts and slow ray tracing pipeline creation at runtime.

VITE_RT_PSO_DEBLOAT cuts the permutation set down to the effects Vite actually ships, by returning false from ShouldCompilePermutation for everything else.

What is compiled out at the default value

With VITE_RT_PSO_DEBLOAT=1, these effects are unavailable regardless of their console variables:

Setting the console variable will appear to succeed and the effect will not render.

What still works

The set that remains is exactly Vite's recommended configuration: DDGI for indirect lighting, RT reflections via the deferred path, and RT shadows and AO. See Global Illumination for why DDGI is preferred over per-pixel ray-traced GI in the first place — the debloat switch encodes that recommendation into the build.

Turning it off

Set VITE_RT_PSO_DEBLOAT=0 and rebuild if you need path tracing for reference imagery, RTXDI for a many-lights scene, or ray-traced translucency and caustics.

Turning this off substantially increases shader compilation time, packaged build size and ray tracing PSO count. Consider maintaining a separate target configuration — debloat off for an internal reference-rendering build, debloat on for the shipping build — rather than turning it off globally.

VITE_O_SSAO

Enables Vite's rewritten memory access pattern for the screen-space ambient occlusion pass. Same visual result as stock, lower cost.

Unusually among these switches, it also has a runtime CVar — but only in development builds:

r.Vite.SSAO 0   // stock UE path
r.Vite.SSAO 1   // optimised path

Shipping builds are locked to the compile-time value; the CVar does not exist. The runtime toggle exists so the two paths can be A/B compared during development, which is how the optimisation was validated. There is no reason to turn the compile-time switch off. See Ambient Occlusion.

VITE_PHYSX_FIXED_TIMESTEP

Off by default. Enables deterministic fixed-step PhysX simulation with render interpolation, plus the p.VitePhysXFixedTimestep.* console variables.

The compile-time gate exists because the feature adds branches and double-buffered transform storage to the physics scene, substep task and animation physics blend. Projects with no determinism requirement should not pay for it. Full documentation is in Fixed Timestep.

VITE_DLSS_PATCH

Off by default. Adds TranslucencyAfterDOFUpscaledRT and TranslucencyAfterDOFModulateUpscaledRT mesh passes so selected translucent primitives render at output resolution after upscaling, and adds r.VolumetricFog.UseUpScaledSizeVolumetricFog so the fog grid can be computed from output resolution.

Only relevant to projects shipping with an upscaler enabled. See Upscalers and Frame Generation.

VITE_NVRTX_TRANSLUCENCY_DEPTH

Off by default. Allocates and writes a separate translucency depth texture alongside separate translucency colour, inherited from the NvRTX branch. Required by some NvRTX effects that need translucent depth; costs an extra render target when enabled.

Checking what a build has

Compile-time switches are invisible at runtime, which makes "is this feature even compiled in?" a real question when debugging.

The most reliable check is to set the relevant CVar and see whether the effect appears. If r.RayTracing.SampledDirectLighting 1 produces no change in a scene with hundreds of lights, VITE_RT_PSO_DEBLOAT is on.

For the switches with runtime CVars, checking whether the CVar exists at all is a direct test: in a Shipping build, r.Vite.SSAO will not be found because it is compiled out.

See also

• Shader Compilation and PSO
• Ray Tracing
• Fixed Timestep
• Cache Management
• Build from Source