refactor: move world concepts into engine

engine/world/Collider.ts

@@ -0,0 +1,116 @@
+import type { Vec3 } from "../math/Vec3"
+
+/** A 2.5D box: horizontal footprint plus top height. */
+export type BoxCollider = {
+  shape: "box"
+  minX: number
+  maxX: number
+  minZ: number
+  maxZ: number
+  top: number
+  standable: boolean
+}
+
+/** A 2.5D circle: horizontal footprint plus top height. */
+export type CircleCollider = {
+  shape: "circle"
+  x: number
+  z: number
+  radius: number
+  top: number
+  standable: boolean
+}
+
+/** Finite engine collision capabilities, not game-content identity. */
+export type Collider = BoxCollider | CircleCollider
+
+export namespace Collider {
+  export function centerX(collider: Collider): number {
+    return collider.shape === "circle"
+      ? collider.x
+      : (collider.minX + collider.maxX) * 0.5
+  }
+
+  export function centerZ(collider: Collider): number {
+    return collider.shape === "circle"
+      ? collider.z
+      : (collider.minZ + collider.maxZ) * 0.5
+  }
+
+  export function contains(collider: Collider, x: number, z: number): boolean {
+    if (collider.shape === "circle") {
+      const dx = x - collider.x
+      const dz = z - collider.z
+      return dx * dx + dz * dz <= collider.radius * collider.radius
+    }
+    return (
+      x >= collider.minX &&
+      x <= collider.maxX &&
+      z >= collider.minZ &&
+      z <= collider.maxZ
+    )
+  }
+
+  /** Push a horizontal player circle out of one collider. */
+  export function pushOut(
+    collider: Collider,
+    position: Vec3,
+    radius: number,
+  ): void {
+    if (collider.shape === "circle") {
+      pushFromCircle(position, radius, collider)
+      return
+    }
+    pushFromBox(position, radius, collider)
+  }
+
+  function pushFromBox(position: Vec3, radius: number, box: BoxCollider): void {
+    const cx = Math.max(box.minX, Math.min(box.maxX, position.x))
+    const cz = Math.max(box.minZ, Math.min(box.maxZ, position.z))
+    const dx = position.x - cx
+    const dz = position.z - cz
+    const distanceSquared = dx * dx + dz * dz
+    if (distanceSquared >= radius * radius) {
+      return
+    }
+    if (distanceSquared > 1e-6) {
+      const distance = Math.sqrt(distanceSquared)
+      const push = (radius - distance) / distance
+      position.x += dx * push
+      position.z += dz * push
+      return
+    }
+    const left = position.x - box.minX
+    const right = box.maxX - position.x
+    const near = position.z - box.minZ
+    const far = box.maxZ - position.z
+    const nearest = Math.min(left, right, near, far)
+    if (nearest === left) {
+      position.x = box.minX - radius
+    } else if (nearest === right) {
+      position.x = box.maxX + radius
+    } else if (nearest === near) {
+      position.z = box.minZ - radius
+    } else {
+      position.z = box.maxZ + radius
+    }
+  }
+
+  function pushFromCircle(
+    position: Vec3,
+    radius: number,
+    circle: CircleCollider,
+  ): void {
+    const dx = position.x - circle.x
+    const dz = position.z - circle.z
+    const reach = radius + circle.radius
+    const distanceSquared = dx * dx + dz * dz
+    if (distanceSquared >= reach * reach || distanceSquared < 1e-6) {
+      return
+    }
+    const distance = Math.sqrt(distanceSquared)
+    const push = (reach - distance) / distance
+    position.x += dx * push
+    position.z += dz * push
+  }
+}