refactor: move world concepts into engine

engine/world/CollisionWorld.ts

@@ -0,0 +1,62 @@
+import type { Vec3 } from "../math/Vec3"
+import { Collider, type Collider as ColliderShape } from "./Collider"
+import type { Terrain } from "./Terrain"
+
+export type CollisionWorld = {
+  terrain: Terrain
+  staticColliders: ColliderShape[]
+  dynamicColliders: ColliderShape[]
+}
+
+export namespace CollisionWorld {
+  export function create(
+    terrain: Terrain,
+    staticColliders: ColliderShape[],
+  ): CollisionWorld {
+    return { terrain, staticColliders, dynamicColliders: [] }
+  }
+
+  export function pushOut(
+    world: CollisionWorld,
+    position: Vec3,
+    radius: number,
+  ): void {
+    pushFrom(world.staticColliders, position, radius)
+    pushFrom(world.dynamicColliders, position, radius)
+  }
+
+  export function groundHeight(world: CollisionWorld, position: Vec3): number {
+    let ground = world.terrain.heightAt(position.x, position.z)
+    ground = standingHeight(world.staticColliders, position, ground)
+    return standingHeight(world.dynamicColliders, position, ground)
+  }
+
+  function pushFrom(
+    colliders: ColliderShape[],
+    position: Vec3,
+    radius: number,
+  ): void {
+    for (const collider of colliders) {
+      if (position.y < collider.top - 0.01) {
+        Collider.pushOut(collider, position, radius)
+      }
+    }
+  }
+
+  function standingHeight(
+    colliders: ColliderShape[],
+    position: Vec3,
+    initial: number,
+  ): number {
+    let ground = initial
+    for (const collider of colliders) {
+      if (
+        collider.standable &&
+        Collider.contains(collider, position.x, position.z)
+      ) {
+        ground = Math.max(ground, collider.top)
+      }
+    }
+    return ground
+  }
+}