Glossary
Vite and fork terminology
- Vite
This engine: a fork of Unreal Engine 4.27 based on NVIDIA's NvRTX branches, focused on performance and rendering technology that 4.27 does not ship with upstream. Engine association identifier
UE_ViteFork.- NvRTX
NVIDIA's public Unreal Engine branches carrying their ray tracing technology ahead of upstream. Vite draws from NvRTX 4.27 Caustics and NvRTX 5.0.
- VITE_* switch
A compile-time preprocessor switch controlling whether a feature is built into the engine at all. Defined in
Engine\Source\Runtime\Core\Public\Misc\CoreDefines.h. Changing one requires an engine rebuild. See Compile-Time Switches.- Compiled out
A feature whose shader permutations and code paths are excluded from the build by a compile-time switch. Its console variables still exist and set successfully; nothing renders. The most common cause of "this setting does nothing" in Vite.
- Debloat
The process of removing unused platform binaries, templates, samples and plugins from the engine tree to reduce disk footprint. See Debloat Guide.
- Installed build
A precompiled, redistributable engine that works like a launcher install. Cannot compile engine C++. See Installed Builds.
Rendering
- DDGI
Dynamic Diffuse Global Illumination. NVIDIA's probe-based GI technique, provided by the RTXGI plugin. Probes store irradiance and depth; surfaces sample the surrounding probes for indirect light. Vite's recommended dynamic GI. See Dynamic DDGI.
- SSGI
Screen Space Global Illumination. Derives indirect light from the rendered frame. Cheap and detailed but limited to what is on screen. Usually layered under DDGI rather than used alone. See SSGI.
- RTXDI
RTX Direct Illumination. Ray-traced direct lighting for scenes with very many lights, using reservoir resampling. Vite has the standalone version, not the Lumen-integrated one from UE 5.1+. Compiled out by default. See RTXDI.
- ReSTIR / reservoir resampling
The sampling technique behind RTXDI. Each pixel maintains a reservoir of light samples that is refined spatially and temporally, so a small number of rays approximates a much larger light set.
- Path tracing
Full light transport simulation. Reference quality, not a runtime target. Compiled out by default. See Path Tracing.
- DXR
DirectX Raytracing. The API behind every ray-traced feature in Vite, and the reason they all require DirectX 12.
- PSO
Pipeline State Object. A compiled bundle of shader and fixed-function state. Ray tracing PSOs are large and slow to build, which is what
VITE_RT_PSO_DEBLOATexists to reduce. See Shader Compilation and PSO.- Shader permutation
One compiled variant of a shader for a specific combination of features. Permutation count multiplies: each shading model, each optional feature and each quality level widens the set. The dominant factor in shader compile time and package size.
- Caustics
Light focused by refraction or reflection through transparent or specular surfaces. Vite has both mesh caustics and water caustics from the NvRTX Caustics branch. Compiled out by default. See RT Translucency and Caustics.
- Callisto BRDF
A Vite-specific shading model for characters and skin, exposing retroreflection, diffuse Fresnel and terminator smoothing by repurposing standard material pins. See Shading Models.
- Shadow terminator
The boundary between lit and unlit regions on a curved surface. Its hardness is one of the most visible tells of real-time rendering; Callisto BRDF exposes direct control over it.
- SMAA
Subpixel Morphological Anti-Aliasing. Vite's recommended anti-aliasing method. Spatial rather than temporal, so it does not introduce the ghosting and smearing TAA does. See Anti-Aliasing.
- TAA
Temporal Anti-Aliasing. Unreal's default. Accumulates samples across frames; effective but introduces ghosting, smearing and softness on motion.
- HBAO+
NVIDIA's Horizon-Based Ambient Occlusion. Higher quality than standard SSAO, multiplying over the screen-space AO buffer. Works on DX11 and D3D12 despite help text to the contrary. See Ambient Occlusion.
- Tessellation
Hardware subdivision of triangles on the GPU, driving displacement. Removed in UE5 in favour of Nanite; retained in Vite. See Tessellation.
- TressFX
AMD's strand-based hair rendering and simulation system. Version 5.0 is bundled. An alternative to Unreal's Groom system. See Hair Rendering.
- NRD / ReLAX
NVIDIA Real-Time Denoiser. Cleans up the noise inherent in low-sample-count ray tracing. Enabled by default.
Upscaling
- DLSS
NVIDIA Deep Learning Super Sampling. Renders at lower resolution and reconstructs, using an AI model. NVIDIA hardware only. Vite bundles 4.5. See Upscalers.
- DLAA
Deep Learning Anti-Aliasing. DLSS's reconstruction applied at native resolution — quality rather than performance.
- Ray Reconstruction
DLSS component that replaces hand-tuned ray tracing denoisers with a learned one.
- FSR
AMD FidelityFX Super Resolution. Cross-vendor upscaling. Vite bundles FSR 4.1.1, which is DX12-only.
- XeSS
Intel Xe Super Sampling. Cross-vendor, with a faster path on Intel Arc hardware. Vite bundles 3.0.5.
- NIS
NVIDIA Image Scaling. Spatial upscaling with no temporal component. The cheapest and lowest-quality option, but it works everywhere.
- Streamline
NVIDIA's plugin layer providing DLSS Frame Generation and Reflex.
- Frame generation
Synthesising intermediate frames between rendered ones. Increases displayed frame rate without reducing input latency, and slightly increases it.
- Reflex
NVIDIA's input latency reduction technology, which matters more once frame generation is in play.
Physics
- PhysX
NVIDIA's physics engine, Unreal's default through 4.27. Retained by Vite rather than migrating to Chaos. See PhysX.
- Chaos
Epic's physics engine, which replaced PhysX in UE5. Vite does not use it.
- Apex Destruction
PhysX's destructible mesh system. Removed in UE5; retained in Vite. See Destruction and Cloth.
- Apex Cloth
PhysX's cloth simulation. Removed in UE5; retained in Vite.
- Blast
NVIDIA's newer destruction library, more flexible than Apex Destruction. Bundled with separate runtime and authoring plugins.
- Fixed timestep
Advancing physics by a constant delta regardless of frame time, giving frame-rate-independent determinism. Optional in Vite behind
VITE_PHYSX_FIXED_TIMESTEP. See Fixed Timestep.- Substepping
Subdividing a frame's physics update into smaller steps for stability. Distinct from fixed timestep, which also fixes the step size across frames.
- CCD
Continuous Collision Detection. Sweeps a body's motion between frames rather than testing only its endpoints, preventing fast objects from tunnelling through thin geometry. More expensive than discrete detection.
- CMC
Character Movement Component. Unreal's standard character locomotion component, and one of the most expensive per-instance costs in a crowd scene. See 400 Characters CMC Bench.
Engine and build
- DDC
Derived Data Cache. Where compiled shaders, cooked textures and other derived artefacts are stored. See Cache Management.
- UAT / UBT
Unreal Automation Tool and Unreal Build Tool. UAT drives high-level operations such as installed builds and packaging; UBT compiles.
- BuildGraph
UAT's XML-driven build orchestration system, used to produce installed builds.
- ISM / HISM
Instanced Static Mesh and Hierarchical Instanced Static Mesh components. Render many copies of one mesh in a small number of draw calls. The rendering side of the PhysX Instanced Subsystem.
- ABI
Application Binary Interface. In Vite's context, the binary layout of structures shared between CPU and GPU. Changing one breaks PSO caching, serialization and ray tracing stability, and is grounds for immediate rejection of a contribution. See Coding Guidelines.
- ACL
Animation Compression Library. Replaces Unreal's built-in animation compression with a substantially better size-to-quality curve.
- Motion matching
Selecting animation frames at runtime by matching current pose and trajectory against a database, rather than following a state machine. Provided by the Motion Symphony plugin.