Virtualised geometry (Nanite)

Virtualised geometry is a way of rendering meshes in which the engine keeps the full-detail source, streams in only the parts the camera needs, and scales the triangle count with screen resolution (Unreal Engine Documentation: Nanite Virtualized Geometry). Unreal Engine 5's Nanite is the best-known example. 80 Level's summary of Epic's SIGGRAPH talk puts it as doing work "on only the detail that can be perceived and no more" (80 Level: A Deep Dive into Unreal Engine's 5 Nanite). Compare virtual texturing, which applies a similar streaming idea to textures.

For environment artists, Nanite changes what a triangle budget means, replaces most hand-made LODs for static meshes, and largely removes draw calls as a limit. It also brings new costs and limits, covered below.

#How it works, at artist level

You do not need the maths, but a mental model helps you make better assets.

1. On import, the mesh is cut into clusters. Each cluster holds 128 triangles (SIGGRAPH 2021: Nanite: A Deep Dive).
2. A hierarchy is built. Neighbouring clusters are grouped, merged, simplified to about half the triangles, and split again into 128-triangle clusters, repeating until one root remains (SIGGRAPH 2021: Nanite: A Deep Dive).
3. At runtime, the engine picks clusters by screen error. For each part of the mesh, it draws the coarsest clusters whose simplification error, projected to screen pixels, is small enough (SIGGRAPH 2021: Nanite: A Deep Dive). Clusters "are swapped on the fly at varying levels of detail based on the camera view", and neighbours join without cracks (Unreal Engine Documentation: Nanite Virtualized Geometry).
4. Data streams on demand. Only visible detail needs to be in memory, which is why Epic recommends SSDs (Unreal Engine Documentation: Nanite Virtualized Geometry).
5. Tiny triangles get a special path. Clusters with triangles smaller than 32 pixels are rasterised in software, which Karis reports is about three times faster on average than their fastest hardware-rasteriser path (SIGGRAPH 2021: Nanite: A Deep Dive).

#What Nanite supports today

Support has grown with each release. The list below follows Epic's current documentation (Unreal Engine Documentation: Nanite Virtualized Geometry) unless noted.

Not supported (Unreal Engine Documentation: Nanite Virtualized Geometry): morph targets, forward rendering, stereo VR rendering, MSAA, lighting channels, and per-view filtering by minimum screen radius or distance culling. Ray tracing uses a simplified fallback mesh by default.

#What it costs

Disk. Nanite meshes average 14.4 bytes per input triangle, so a one-million-triangle mesh is about 13.8 MB on disk (Unreal Engine Documentation: Nanite Technical Details). By default Nanite keeps every source triangle; Keep Triangle Percent and Trim Relative Error reduce disk size, which Epic frames as being about download size, "not specifically for improving performance" (Unreal Engine Documentation: Nanite Technical Details).

Memory for instances. Karis gives 457 MB for the transforms of 10 million instances (SIGGRAPH 2021: Nanite: A Deep Dive). Scenes are hard-limited to 16 million streamed-in instances (Unreal Engine Documentation: Nanite Virtualized Geometry).

Shading. Masked materials in Nanite "incur a significant cost during base pass shading"; on Fortnite, the team often chose more triangles with opaque materials instead (Unreal Engine tech blog: Bringing Nanite to Fortnite Battle Royale in…).

Overdraw. Foliage and other "aggregate" geometry perform worse in Nanite, partly because of overdraw (SIGGRAPH 2021: Nanite: A Deep Dive). Epic notes that "smaller objects that are closely stacked together create more overdraw than larger ones" (Unreal Engine Documentation: Nanite Technical Details).

Hardware. Nanite targets current console and desktop platforms with DirectX 12 and Shader Model 6 (Unreal Engine Documentation: Nanite Virtualized Geometry).

#When to use Nanite

Epic says Nanite "should generally be enabled wherever possible on platforms that support it" (Unreal Engine Documentation: Nanite Virtualized Geometry). Good candidates: meshes with many triangles or tiny on-screen triangles, many instances, large occluders, and meshes casting Virtual Shadow Map shadows (Unreal Engine Documentation: Nanite Virtualized Geometry). Fortnite found large non-Nanite meshes render shadows into Virtual Shadow Maps more slowly than equivalent Nanite meshes (Unreal Engine tech blog: Bringing Nanite to Fortnite Battle Royale in…).

Consider other options when:

• The target has no Nanite: mobile, standalone VR, or a game shipping on both Nanite and non-Nanite hardware (you will need classic LODs too).
• The material is translucent, or needs features Nanite does not support.
• Masked cards dominate, such as old-style card foliage, where opaque geometry may be cheaper (Unreal Engine tech blog: Bringing Nanite to Fortnite Battle Royale in…).
• The mesh is a sky sphere, Epic's own example of large triangles, no occlusion and a single instance, though it says the loss there is minimal (Unreal Engine Documentation: Nanite Virtualized Geometry).

#Similar approaches elsewhere

Nanite's cluster-hierarchy idea has also been applied outside Unreal's meshes. A 2025 SIGGRAPH paper, Virtualized 3D Gaussians, applies a cluster-based LOD system to Gaussian splat scenes and states it is "inspired by Unreal Engine 5's Nanite system" (Yang et al. 2025). It reports better speed and quality trade-offs, with storage roughly doubling (Yang et al. 2025). For other game engines, no comparable built-in system could be verified for this page; check your engine's current documentation.

#Practical tips for artists

• Enable Nanite on import with Build Nanite, and turn off Generate Lightmap UVs if you do not use baked lighting, to save import time and data (Unreal Engine Documentation: Nanite Virtualized Geometry).
• Use Preserve Area on foliage that thins at distance; Epic says it "should be enabled on all foliage meshes and nothing else" (Unreal Engine Documentation: Nanite Technical Details).
• Clamp World Position Offset so clusters are culled correctly (Unreal Engine Documentation: Nanite Virtualized Geometry).
• Trim source data for download size when needed, using Keep Triangle Percent (Unreal Engine Documentation: Nanite Technical Details). See decimation.
• Watch for tangent seams. Nanite derives tangents in the pixel shader instead of storing them, which can cause edge discontinuities (Unreal Engine Documentation: Nanite Virtualized Geometry). See tangent space and MikkTSpace.

#Common mistakes

• Importing raw multi-million-triangle scans everywhere. It works, but the download grows by about 13.8 MB per million triangles (Unreal Engine Documentation: Nanite Technical Details).
• Keeping unique 4K normal maps on Nanite meshes. Epic's comparison shows they remove the size advantage (Unreal Engine Documentation: Nanite Technical Details).
• Using masked materials by habit. Model the shape instead where you can (Unreal Engine tech blog: Bringing Nanite to Fortnite Battle Royale in…).
• Forgetting the fallback mesh. Ray tracing and unsupported platforms use it (Unreal Engine Documentation: Nanite Virtualized Geometry).

#Further reading and watching