auto-git:

[add] src/rendering/terrain-layer-material.ts
 [add] tests/domain/terrains.test.ts
 [change] src/app/App.tsx
 [change] src/core/terrain-brush.ts
 [change] src/document/migrate-scene-document.ts
 [change] src/document/scene-document-validation.ts
 [change] src/document/scene-document.ts
 [change] src/document/terrains.ts
 [change] src/geometry/terrain-brush.ts
 [change] src/geometry/terrain-mesh.ts
 [change] src/runtime-three/rapier-collision-world.ts
 [change] src/runtime-three/runtime-host.ts
 [change] src/runtime-three/runtime-scene-build.ts
 [change] src/viewport-three/ViewportCanvas.tsx
 [change] src/viewport-three/ViewportPanel.tsx
 [change] src/viewport-three/viewport-host.ts
 [change] tests/domain/build-runtime-scene.test.ts
 [change] tests/domain/rapier-collision-world.test.ts
 [change] tests/domain/terrain.command.test.ts
 [change] tests/domain/water-material.test.ts
 [change] tests/geometry/terrain-brush.test.ts
 [change] tests/geometry/terrain-mesh.test.ts
 [change] tests/serialization/scene-document-json.test.ts
 [change] tests/unit/terrain-foundation.integration.test.tsx
 [change] tests/unit/viewport-canvas.test.tsx

src/runtime-three/rapier-collision-world.ts

@@ -19,6 +19,7 @@ import { getFirstPersonPlayerShapeSignature } from "./player-collision";
 import type {
   RuntimeBrushTriMeshCollider,
   RuntimeNpcCollider,
+  RuntimeTerrainHeightfieldCollider,
   RuntimeSceneCollider
 } from "./runtime-scene-build";
 
@@ -86,7 +87,11 @@ function scaleBoundsCenter(bounds: { min: Vec3; max: Vec3 }, scale: Vec3): Vec3
   };
 }
 
-function createRapierHeightfieldHeights(collider: GeneratedModelHeightfieldCollider): Float32Array {
+function createRapierHeightfieldHeights(collider: {
+  rows: number;
+  cols: number;
+  heights: ArrayLike<number>;
+}): Float32Array {
   const heights = new Float32Array(collider.heights.length);
 
   // Rapier's heightfield samples are column-major, with the Z axis varying
@@ -182,6 +187,45 @@ function attachTerrainModelCollider(world: RAPIER.World, collider: GeneratedMode
   );
 }
 
+function attachTerrainCollider(
+  world: RAPIER.World,
+  collider: RuntimeTerrainHeightfieldCollider
+) {
+  if (collider.rows < 2 || collider.cols < 2) {
+    throw new Error(
+      `Terrain collider ${collider.terrainId} must have at least a 2x2 height sample grid.`
+    );
+  }
+
+  const body = world.createRigidBody(
+    RAPIER.RigidBodyDesc.fixed().setTranslation(
+      collider.position.x,
+      collider.position.y,
+      collider.position.z
+    )
+  );
+  const rowSubdivisions = collider.rows - 1;
+  const colSubdivisions = collider.cols - 1;
+
+  world.createCollider(
+    RAPIER.ColliderDesc.heightfield(
+      rowSubdivisions,
+      colSubdivisions,
+      createRapierHeightfieldHeights(collider),
+      {
+        x: collider.maxX - collider.minX,
+        y: 1,
+        z: collider.maxZ - collider.minZ
+      }
+    ).setTranslation(
+      (collider.minX + collider.maxX) * 0.5,
+      0,
+      (collider.minZ + collider.maxZ) * 0.5
+    ),
+    body
+  );
+}
+
 function attachDynamicModelCollider(world: RAPIER.World, collider: GeneratedModelCompoundCollider) {
   const body = createFixedBodyForModelCollider(world, collider);
 
@@ -385,6 +429,11 @@ export class RapierCollisionWorld {
     });
 
     for (const collider of colliders) {
+      if (collider.source === "terrain") {
+        attachTerrainCollider(world, collider);
+        continue;
+      }
+
       if (collider.source === "brush") {
         attachBrushCollider(world, collider);
         continue;