refactor: move world concepts into engine

game/actors/trees/Spruce.ts

@@ -1,20 +1,63 @@
 import type { Mesh } from "../../../engine/scene/Mesh"
-import type { Tree, TreeSpecies } from "../Tree"
+import type { Material } from "../../../engine/render/Material"
+import type { Prefab } from "../../../engine/scene/Prefab"
+import type { Tree } from "../Tree"
 import { cone, lerp, limb, rng } from "./treekit"
 
 // Spruce: tall thin trunk under stacked cones that narrow to a point (tiered, taller
 // than wide). Trunk = brown bark, foliage = spruce needle.
 
-export const spruce: TreeSpecies = { kind: "spruce", trunk: "bark", foliage: "needle", build }
+export type Spruce = Prefab<Tree>
 
-function build(tree: Tree, trunk: Mesh, needles: Mesh, lod: "full" | "impostor"): void {
+export namespace Spruce {
+  export function create(trunk: Material, foliage: Material): Spruce {
+    return {
+      position: (tree) => tree.position,
+      bakeNear: (tree, batch) =>
+        build(tree, batch.mesh(trunk), batch.mesh(foliage), "full"),
+      bakeFar: (tree, batch) =>
+        build(tree, batch.mesh(trunk), batch.mesh(foliage), "impostor"),
+      collider: treeCollider,
+    }
+  }
+
+  function treeCollider(tree: Tree) {
+    if (tree.growth <= 0.35) {
+      return null
+    }
+    const radius = tree.growth * 0.2 + 0.15
+    return {
+      shape: "box" as const,
+      minX: tree.position.x - radius,
+      maxX: tree.position.x + radius,
+      minZ: tree.position.z - radius,
+      maxZ: tree.position.z + radius,
+      top: tree.position.y + 3,
+      standable: false,
+    }
+  }
+}
+
+function build(
+  tree: Tree,
+  trunk: Mesh,
+  needles: Mesh,
+  lod: "full" | "impostor",
+): void {
   const base = tree.position
   const g = tree.growth
   const rand = rng(tree.seed)
   const h = lerp(0.6, 9, g)
   const rTrunk = lerp(0.03, 0.2, g)
   const impostor = lod === "impostor"
-  limb(trunk, base, { x: base.x, y: base.y + h, z: base.z }, rTrunk, rTrunk * 0.25, impostor ? 3 : 5)
+  limb(
+    trunk,
+    base,
+    { x: base.x, y: base.y + h, z: base.z },
+    rTrunk,
+    rTrunk * 0.25,
+    impostor ? 3 : 5,
+  )
 
   // Stacked cones: widest low, shrinking to a point up top -> conical tiers. The
   // impostor keeps the first two tiers at low sides (same seed => aligned).