PolyTerrain mesh terrain

Dawn Engine PolyTerrain is a true 3D mesh terrain system (also known in code as PolyPartition). Unlike heightfield terrain, it can express overhangs, caves, tunnels, and steep cliffs as editable triangle meshes, with a non-destructive modifier stack, weight-channel painting, deterministic bake, and optional runtime virtual texturing.

Maturity: shipped. Provided by the PolyTerrain Gem. Off by default—enable it in the Settings Registry before authoring. It is independent from the heightfield Terrain Gem; both can coexist in one level.

It does not replace heightfield terrain: open plains and clipmap-style far terrain still use Gems/Terrain. Use PolyTerrain where mesh topology is required.

What problem it solves

Heightfields cannot represent multi-valued height (overhangs, caves, stacked decks). Hand-authored static meshes lose the non-destructive edit loop of terrain tools. PolyTerrain provides:

• Base mesh sections with a stack of modifiers (sculpt, paint, boolean, spline, noise, and more);
• Live Preview in the editor and bit-identical Compiled bake for runtime;
• Weight channels for material splat, physics materials, and vegetation tags;
• Bridges to World Streaming, PhysX collision, Atom materials, and optional VT / PCG / multiplayer weight overlays.

With the Gem disabled (/O3DE/PolyTerrain/Enabled=false), heightfield terrain and existing levels behave as before.

How it works

MPD (.polypartitiondefinition)
 │
Poly Partition entity ── Base Sections ── Modifier stack (Priority Layer + Sub-Priority)
 │
 ├─ Preview (editor): same evaluator, in-memory mesh, no disk write
 └─ Build → .polypartition → AP → .polypartitionsection + .polypartitionweights
 │
 PrefabProcessor → runtime section entities (+ WS cells)
 │
 Atom render + PhysX collision (+ optional VT / SurfaceData)

Two rules run through the Gem:

1. Non-destructive authoring: Prefabs store Base + Modifier params; Preview rebuilds on load. Undo is the standard editor undo stack.
2. One evaluator: Preview and Compiled share the same Core evaluation kernel; ContentHash drives incremental AssetProcessor bake.

Large worlds use double-precision section anchors (AZ::Vector3d) and typically pair with double-precision rendering and World Streaming.

Quick start (summary)

1. Enable the PolyTerrain Gem, then set /O3DE/PolyTerrain/Enabled and EditorModeEnabled to true. Restart the editor.
2. Create a Poly Partition Definition (.polypartitiondefinition) with Priority Layers and Weight Channels.
3. Tools → Poly Terrain Mode → Create: make a Poly Partition entity and assign the MPD.
4. Add Sculpt / Weight Paint, iterate in Preview, then Build Compiled Sections.

Sample level: AutomatedTesting/Levels/PolyTerrain/PolyTerrainSample.

For the full walkthrough, Registry gates, and bake checklist, see Getting started.

Handbook chapters

Glossary

Limits and related capabilities

You can rely on:

• Non-destructive modifier stacks; Preview / Compiled parity via one evaluator;
• Weight channels for splat, physics, and SurfaceData; WS cell bake and FarField HLOD contribution;
• Optional VT, GPU preview, PCG graphs, and multiplayer weight-stamp sync.

Do not assume:

• PolyTerrain implements TerrainDataRequestBus (use GetUnifiedSurfacePointD in the editor; runtime gameplay should use compiled meshes / SurfaceData / your own queries);
• Enabling the Gem alone turns on edit mode or VT (separate Registry keys);
• Section entities are networked actors (spawnable / WS authority; only weight overlays replicate when the Multiplayer submodule is built).

Next steps

• Getting started — shortest path to a baked partition.
• World Streaming — bake partitions into streaming cells and FarField HLOD.
• Double-precision rendering — section anchors and large-world authorship.