Update terrain plan

src/features/editScene/TerrainRequirements.md

@@ -432,10 +432,9 @@ m_world.component<TerrainComponent>();
 
 **In `EditorApp::setup()`** — construct after physics but before water/sun/skybox
 (terrain must exist before those systems try to interact with it):
-```cpp
-m_terrainSystem = std::make_unique<TerrainSystem>(
-    m_world, m_sceneMgr, m_physicsSystem.get());
-```
+	Ogre::Camera *cam = m_camera ? m_camera->getCamera() : nullptr;
+	m_terrainSystem = std::make_unique<TerrainSystem>(
+		m_world, m_sceneMgr, cam, m_physicsSystem->getPhysicsWrapper());
 
 **In `EditorApp::frameRenderingQueued()`** — call update **before**
 static-world generation and **after** visual mesh setup. Insert right after
@@ -1012,6 +1011,8 @@ Minimum controls:
   - Add/remove/split/join/select nodes.
   - Inspector for node position, offset, edge levels.
   - "Comply terrain to roads" button.
+	- Physics debug: "Show Terrain Colliders" checkbox (off by default,
+	  toggles `TerrainBodyDrawFilter` via `TerrainSystem`).
 - Prefab spawn mode (uses `TerrainPrefabSpawnerComponent`):
   - Add/remove spawn points (snapped to terrain surface).
   - Pick prefab from existing prefab list.
@@ -1145,15 +1146,63 @@ Definition of done: a paged terrain renders in the editor; terrain pages load
 and unload as the camera moves.
 
 ### Milestone 2 — Physics integration
-- Implement `ZigzagHeightfieldShape` as a `JPH::MeshShape` per page with zigzag
-  triangulation matching Ogre.
-- Queue collider creation after page load and derived-data completion.
-- Maintain `mColliders` map; safe remove/re-add on scene clear or component
-  removal.
-- Add raycast helper to `TerrainSystem` for gameplay/editor tools.
+
+**Changes to TerrainSystem constructor**: Now takes `JoltPhysicsWrapper*` so
+it can create/destroy static terrain collider bodies directly in the Jolt world.
+
+```cpp
+TerrainSystem(flecs::world &world, Ogre::SceneManager *sceneMgr,
+              Ogre::Camera *camera, JoltPhysicsWrapper *physics);
+```
+
+**EditorApp wiring change**: Update `setup()` to pass `m_physicsSystem->getPhysicsWrapper()`.
+
+**Collider creation queue**: After `CustomTerrainDefiner::define()` finishes a
+page and `isDerivedDataUpdateInProgress()` is false, create a per-page
+`JPH::MeshShape` with zigzag triangulation (see section 3.3) and add a static
+body at the page's world position.  Bodies go into `Layers::NON_MOVING`.
+
+**mColliders map**: `std::unordered_map<uint64_t, TerrainCollider>` keyed by
+`packIndex(x, y)`.  `TerrainCollider` holds `{pageX, pageY, JPH::BodyID,
+pendingRemove}`.
+
+**Collider removal queue**: When a page unloads (detected via
+`DummyPageProvider::unloadProceduralPage`), mark its collider `pendingRemove`.
+In `update()`, only remove bodies when no derived data update is in progress.
+
+**Zigzag triangulation** (see section 3.3): Build `JPH::MeshShape` from
+`terrain->getHeightData()` using the zigzag quad split matching Ogre's odd/even
+row parity.
+
+**Debug drawing — TerrainBodyDrawFilter**:
+- Implement `class TerrainBodyDrawFilter : public JPH::BodyDrawFilter` in
+  `TerrainSystem` that tracks terrain `BodyID`s in a `std::set`.
+- `ShouldDraw(const JPH::Body &)` returns `false` for terrain bodies when
+  `m_showTerrainColliders == false` (the default).
+- Add `void setShowTerrainColliders(bool)` toggle.
+- Thread the filter into the physics wrapper: add a
+  `JoltPhysicsWrapper::setBodyDrawFilter(BodyDrawFilter*)` setter and pass it
+  to `BodyManager::DrawBodies(..., filter)`.
+- Terrain editor gets a **"Show Terrain Colliders"** checkbox (off by default).
+
+**Raycast helper**: `TerrainSystem::getHeightAt(const Ogre::Vector3 &worldPos)`
+picks the right page, samples the height data bilinearly, and returns the
+world-space Y.  Also add `raycastTerrain(const Ogre::Ray &ray, float &outT)`
+that casts a ray against all loaded terrain pages' Jolt bodies using
+`JPH::NarrowPhaseQuery::CastRay`.
+
+**Testing**:
+- [ ] Drop a rigid body on terrain → rests flush (no sinking/floating).
+- [ ] Toggle "Show Terrain Colliders" → wireframe matches terrain surface.
+- [ ] Fly away and back → colliders for unloaded pages removed, new pages get colliders.
+- [ ] Remove terrain entity → all collider bodies removed, no dangling Jolt bodies.
+- [ ] Add/remove terrain repeated → stable memory (valgrind/ASan).
+- [ ] Raycast from above hits terrain at correct height.
+- [ ] Colliders are NOT visible in debug draw by default.
 
 Definition of done: rigid bodies and characters collide flush with the visible
-terrain; removing/re-adding the terrain entity is leak-free.
+terrain; terrain collider debug draw is off by default with a toggle; removing
+and re-adding the terrain entity is leak-free.
 
 ### Milestone 3 — Serialization + heightmap editing + splat painting
 - Scene serialization for `TerrainComponent` (save/load JSON round-trip).