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Physics: terrain has no collision — wire Jolt HeightFieldShape into TerrainComponent #428
Description
Problem
Terrain renders fully (quadtree LOD, tessellation, splatmaps, streaming) but has no physics collision. Jolt's heightfield shape is explicitly rejected today:
OloEngine/src/OloEngine/Physics3D/JoltShapes.cpp:542—GetShapeType: HeightField shape type {0} not supported, defaulting to BoxOloEngine/src/OloEngine/Physics3D/JoltBinaryStream.cpp:394reads aHeightFieldcase, but no shape is ever constructed for terrain.- No terrain-collider component exists under
OloEngine/src/OloEngine/Terrain/.
Consequence: the player falls through terrain, NPCs can't walk on it, vehicles can't drive on it.
Why it matters
Genre-blocking for an FPS — collision against the ground is table stakes. This is the single most urgent Tier 1 gap.
Proposed approach
- Build
JPH::HeightFieldShapeSettingsfrom the terrain heightmap (CPU heights already available viaTerrainData::GetHeightAt), matching world scale and tile origin. - Add a
TerrainColliderComponent(or extendTerrainComponent) that creates a static Jolt body from the heightfield on scene start / terrain edit. (Remember the cross-binding touch-points if adding a component.) - For streamed terrain (
TerrainStreamer), create/destroy heightfield bodies per loaded tile; update the dirty region on sculpt/erosion edits (partial heightfield update). - Resolve
JoltShapes.cpp::GetShapeTypeto handleHeightFieldfor serialization round-trip.
Acceptance criteria
- A character controller and a vehicle rest on / drive over terrain without falling through.
- Raycasts (AI perception, weapons) hit the terrain surface.
- Streamed tiles add/remove collision in step with their visual load/unload.
- Sculpt/erosion edits update collision for the affected region.
Tier 1 — architectural. From the "production-ready open-world FPS" gap analysis.
Score
capability: 8
craft: 3
stability: 3
decay: 1
effort: 3
confidence: 0.8
learning: 3
fun: 3
kano: table-stakes
blocked_by: []
blocks: []
Rated per issue-scoring · score = confidence × (capability + craft + stability + decay) / effort, derived by the picker.
Reacted by coderabbitai
Activity
coderabbitai commentedon Jun 28, 2026
🔗 Related PRs
#78 - Feature/physics integration [merged]
#225 - Compute exact mesh collider volume and centroid [merged]
#340 - feat(physics): add CollideConnected toggle for joints (
#308item 1) [merged]🧪 Issue enrichment is currently in open beta.
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drsnuggles8 commentedon Jun 29, 2026
Implemented in PR #468 (branch
feature/physics-terrain-heightfield).What's done
JoltShapes::CreateTerrainHeightFieldShapebuilds a staticJPH::HeightFieldShapefrom the terrain's CPU height field, mappingworldSize/heightScale/entity scale exactly onto Jolt'soffset + scale·(x, sample, z)surface so collision coincides with the rendered mesh. Odd resolutions are padded to Jolt's block-size multiple; bit-depth is adaptive (~2 cm).ShapeType::HeightField+GetShapeTyperound-trip resolved (it was defaulting toBox).JoltScenestatic terrain-body lifecycle onNON_MOVING; bodyUserData= entity UUID so raycasts (AI perception / weapons) resolve back to the terrain entity.TerrainComponent.m_CollisionEnabled(serialized, default on); round-trips through scene YAML + save-game (format v5→v6).OnPhysics3DStart, so it also works headless / on the dedicated server; re-synced on runtimeRegenerate.Evidence (104/104 tests green) — new
TerrainCollisionTest.cppdrives the realScene::OnPhysics3DStart+ Jolt step path, headless:DynamicBodyRestsOnFlatTerrainSurface— a dropped body rests one radius above a flat terrain translated to y=10 (proves no fall-through + transform application).DynamicBodyRestsOnProceduralSurface— a dropped body's rest height tracks the local procedural surface (proves the shape follows the height field; uses an odd resolution to exercise the padding path).RaycastHitsTerrainSurface— a downward ray hits the terrain at the expected surface height and resolves to the terrain entity.All cross-binding coverage guards, save-game round-trips,
SceneSerializer, andLuaDrivesTerrainRegenerationstill pass.Acceptance criteria status
Leaving this open for you to close once PR #468 merges.
fix(physics): tear down terrain collision body on removal; harden inp…
Merge pull request #468 from drsnuggles8/feature/physics-terrain-heig…
drsnuggles8 commentedon Jun 29, 2026
Advanced by #468 (merged 2026-06-29); worktree removed. Static terrain collision delivered: JoltShapes::CreateTerrainHeightFieldShape builds a static JPH::HeightFieldShape body GPU-free from CPU heights at OnPhysics3DStart, ShapeType::HeightField round-trips, TerrainComponent.m_CollisionEnabled persists through scene YAML + save-game, and TerrainCollisionTest proves rest-on-surface + raycast-hit (incl. odd-resolution padding). Two acceptance criteria deferred to a separately-filed follow-up: streamed per-tile collision (TerrainStreamer) and sculpt/erosion dirty-region partial updates (HeightFieldShape::SetHeights). Leaving open pending confirmation those are tracked in the new follow-up issue(s).
drsnuggles8 commentedon Jun 30, 2026
Core scope appears resolved by #468 (merged 2026-06-29):
feat(physics): wire Jolt HeightFieldShape into terrain collision (#428)— buildsJPH::HeightFieldShapeSettingsfrom the terrain heightmap and creates a static collision body (acceptance criteria 1–2). The streamed-tile + sculpt-edit heightfield-update follow-up (acceptance criteria 3–4) is tracked separately in #469. Flagging the core scope for closure.