Terrain Detail Spawning

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Unity's built-in terrain detail system relies on ComputeDetailInstanceTransforms, which runs on the main thread, allocates garbage every frame, and causes hitches — especially with dense vegetation or large terrains.

BRG Instanced Renderer replaces this entirely with a custom detail extraction algorithm that runs on worker threads via the Unity Job System, produces zero garbage, and causes no hitches.

How It Works

The system reads the terrain's detail density maps directly and computes instance transforms in parallel using Burst-compiled jobs. As the camera moves, new terrain patches are loaded and old ones recycled — all without blocking the main thread or allocating managed memory.

Async Terrain Initialization

Reading a terrain's heightmap and holes textures normally blocks the main thread twice per terrain during initialization. With Allow Async Detail Loading enabled (the default), those reads go through an async GPU readback instead, removing both stalls — which matters most when terrains stream in at runtime. The trade-off is that details for a newly initialized terrain don't begin streaming until the readback completes a few frames later. See Terrain Config.

Compatibility

The custom algorithm reproduces the same placement concepts as Unity's built-in system — density maps, per-layer settings, and terrain patch boundaries are all respected. Instance transforms do not match Unity's output exactly on a per-instance basis, but the overall look and coverage is equivalent.

For terrain setup, see Getting Started: Terrain and BRG Terrain Registerer.