LOD system (automatic mesh LOD + LODGroup component)

Motivation

LOD is a fundamental performance tool for any scene with more than a handful of unique meshes. Without it, large environments are off the table for AAA-scale projects.

Goal

An automatic LOD generation pipeline and a runtime LODGroup component that switches mesh detail based on camera distance — matching Godot's GeometryInstance3D LOD or Unity's LODGroup component.

Tasks

Asset pipeline

LODGroup import setting on mesh assets: auto-generate N LOD levels at import (simplify via meshoptimizer or similar)
Manual LOD assignment: drag different mesh assets per LOD level in the Inspector
LOD metadata stored in .meta and cached in the AssetCache

Runtime component

LODGroupComponent: list of (mesh, distance-threshold) pairs; activates the closest matching LOD mesh each frame
Distance computed from main camera transform; supports per-component LOD bias
Integration with MeshRendererComponent (swap mesh, not spawn/destroy GameObjects)
Screen-size-based LOD selection as an alternative mode

Editor

LODGroup Inspector: preview each LOD level + distance slider
Viewport overlay: colour-code objects by current LOD level

Culling

Zero-polygon LOD level = culled (no draw call) — integrate with the frustum culling path

Acceptance Criteria

A mesh with 4 LOD levels switches visibly as the camera moves away.
Auto-generated LODs reduce polygon count by ≥50% per level.
LOD culling level produces zero draw calls.
No per-frame allocation from LOD switching.