refactor: move world concepts into engine

engine/render/Chunk.ts

@@ -0,0 +1,29 @@
+import type { DrawGroup } from "./Material"
+import type { Vec3 } from "../math/Vec3"
+
+export type Bounds3 = {
+  minX: number
+  minY: number
+  minZ: number
+  maxX: number
+  maxY: number
+  maxZ: number
+}
+
+/** One cullable section of static world geometry with two engine-supported LODs. */
+export type Chunk = Bounds3 & {
+  readonly near: readonly DrawGroup[]
+  readonly far: readonly DrawGroup[]
+}
+
+export namespace Chunk {
+  export function isFar(chunk: Chunk, eye: Vec3, lodDistance: number): boolean {
+    if (!(lodDistance < Infinity)) {
+      return false
+    }
+    const dx = eye.x - Math.max(chunk.minX, Math.min(chunk.maxX, eye.x))
+    const dy = eye.y - Math.max(chunk.minY, Math.min(chunk.maxY, eye.y))
+    const dz = eye.z - Math.max(chunk.minZ, Math.min(chunk.maxZ, eye.z))
+    return dx * dx + dy * dy + dz * dz > lodDistance * lodDistance
+  }
+}