Glossary

Terminology used throughout this documentation. Vite-specific terms are marked; the rest are standard Unreal or graphics vocabulary that these docs assume.

Vite and fork terminology

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. 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. 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. 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. The process of removing unused platform binaries, templates, samples and plugins from the engine tree to reduce disk footprint. See Debloat Guide. A precompiled, redistributable engine that works like a launcher install. Cannot compile engine C++. See Installed Builds.

Rendering

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. 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. 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. 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. Full light transport simulation. Reference quality, not a runtime target. Compiled out by default. See Path Tracing. DirectX Raytracing. The API behind every ray-traced feature in Vite, and the reason they all require DirectX 12. 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_DEBLOAT exists to reduce. See Shader Compilation and PSO. 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. 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. A Vite-specific shading model for characters and skin, exposing retroreflection, diffuse Fresnel and terminator smoothing by repurposing standard material pins. See Shading Models. 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. 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. Temporal Anti-Aliasing. Unreal's default. Accumulates samples across frames; effective but introduces ghosting, smearing and softness on motion. 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. Hardware subdivision of triangles on the GPU, driving displacement. Removed in UE5 in favour of Nanite; retained in Vite. See Tessellation. AMD's strand-based hair rendering and simulation system. Version 5.0 is bundled. An alternative to Unreal's Groom system. See Hair Rendering. NVIDIA Real-Time Denoiser. Cleans up the noise inherent in low-sample-count ray tracing. Enabled by default.

Upscaling

NVIDIA Deep Learning Super Sampling. Renders at lower resolution and reconstructs, using an AI model. NVIDIA hardware only. Vite bundles 4.5. See Upscalers. Deep Learning Anti-Aliasing. DLSS's reconstruction applied at native resolution — quality rather than performance. DLSS component that replaces hand-tuned ray tracing denoisers with a learned one. AMD FidelityFX Super Resolution. Cross-vendor upscaling. Vite bundles FSR 4.1.1, which is DX12-only. Intel Xe Super Sampling. Cross-vendor, with a faster path on Intel Arc hardware. Vite bundles 3.0.5. NVIDIA Image Scaling. Spatial upscaling with no temporal component. The cheapest and lowest-quality option, but it works everywhere. NVIDIA's plugin layer providing DLSS Frame Generation and Reflex. Synthesising intermediate frames between rendered ones. Increases displayed frame rate without reducing input latency, and slightly increases it. NVIDIA's input latency reduction technology, which matters more once frame generation is in play.

Physics

NVIDIA's physics engine, Unreal's default through 4.27. Retained by Vite rather than migrating to Chaos. See PhysX. Epic's physics engine, which replaced PhysX in UE5. Vite does not use it. PhysX's destructible mesh system. Removed in UE5; retained in Vite. See Destruction and Cloth. PhysX's cloth simulation. Removed in UE5; retained in Vite. NVIDIA's newer destruction library, more flexible than Apex Destruction. Bundled with separate runtime and authoring plugins. 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. Subdividing a frame's physics update into smaller steps for stability. Distinct from fixed timestep, which also fixes the step size across frames. 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. 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

Derived Data Cache. Where compiled shaders, cooked textures and other derived artefacts are stored. See Cache Management. Unreal Automation Tool and Unreal Build Tool. UAT drives high-level operations such as installed builds and packaging; UBT compiles. UAT's XML-driven build orchestration system, used to produce installed builds. 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. 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. Animation Compression Library. Replaces Unreal's built-in animation compression with a substantially better size-to-quality curve. 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.