diff --git a/engine/Polygon.ts b/engine/Polygon.ts
index 3a64d96..f22b2b3 100644
--- a/engine/Polygon.ts
+++ b/engine/Polygon.ts
@@ -1,4 +1,4 @@
-import { createVector, setEdgeNormal, type Vector } from "#/engine/Vector.ts";
+import { createVector, setUnitNormal, type Vector } from "#/engine/Vector.ts";
 
 export type Polygon = {
 	position: Vector;
@@ -24,9 +24,9 @@ export function updateAxes({ points, axes }: Polygon): void {
 
 	for (let i = 0; i < cap; i++) {
 		const pj = points[i + 1];
-		setEdgeNormal(axes[i], pi, pj);
+		setUnitNormal(axes[i], pi, pj);
 		pi = pj;
 	}
 
-	setEdgeNormal(axes[cap], pi, p0);
+	setUnitNormal(axes[cap], pi, p0);
 }
diff --git a/engine/Vector.ts b/engine/Vector.ts
index 5fe37d6..36bfb0a 100644
--- a/engine/Vector.ts
+++ b/engine/Vector.ts
@@ -47,24 +47,22 @@ export function getSquared(vector: Vector): number {
 	return vector.x * vector.x + vector.y * vector.y;
 }
 
-export function setDistanceNormal(normal: Vector, a: Vector, b: Vector): void {
+export function setUnit(unit: Vector, a: Vector, b: Vector): void {
 	const dx = a.x - b.x;
 	const dy = a.y - b.y;
-	const distance = Math.sqrt(dx * dx + dy * dy);
+	const inv = 1.0 / Math.sqrt(dx * dx + dy * dy);
 
-	if (distance > 0) {
-		normal.x = dx / distance;
-		normal.y = dy / distance;
-	}
+	unit.x = dx * inv;
+	unit.y = dy * inv;
 }
 
-export function setEdgeNormal(normal: Vector, a: Vector, b: Vector): void {
-	const nx = -(b.y - a.y);
+export function setUnitNormal(unit: Vector, a: Vector, b: Vector): void {
+	const nx = a.y - b.y;
 	const ny = b.x - a.x;
 	const inv = 1.0 / Math.sqrt(nx * nx + ny * ny);
 
-	normal.x = nx * inv;
-	normal.y = ny * inv;
+	unit.x = nx * inv;
+	unit.y = ny * inv;
 }
 
 export function getDotProduct(a: Vector, b: Vector): number {
@@ -81,13 +79,9 @@ export function scale(vector: Vector, scalar: number): void {
 }
 
 export function normalize(vector: Vector): void {
-	const magnitude = Math.sqrt(vector.x * vector.x + vector.y * vector.y);
-
-	if (magnitude > 0) {
-		const scalar = 1 / magnitude;
-		vector.x *= scalar;
-		vector.y *= scalar;
-	}
+	const inv = 1.0 / Math.sqrt(vector.x * vector.x + vector.y * vector.y);
+	vector.x *= inv;
+	vector.y *= inv;
 }
 
 export function isZero(vector: Vector): boolean {
diff --git a/engine/dev/GraphBrowser.tsx b/engine/dev/GraphBrowser.tsx
index abc011a..8a40bb1 100644
--- a/engine/dev/GraphBrowser.tsx
+++ b/engine/dev/GraphBrowser.tsx
@@ -12,7 +12,7 @@ import {
 	createVector,
 	getDistance,
 	scale,
-	setDistanceNormal,
+	setUnit,
 	type Vector,
 } from "#/engine/Vector.ts";
 
@@ -104,7 +104,7 @@ function hookEdge<T extends PhysicsPartial>([a, b]: Edge<T>): void {
 	const stiffness = 0.05;
 
 	const direction = createVector();
-	setDistanceNormal(direction, a.position, b.position);
+	setUnit(direction, a.position, b.position);
 
 	const distance = getDistance(a.position, b.position);
 	const magnitude = (distance - restLength) * stiffness + Number.EPSILON;
diff --git a/engine/system/processPhysics.ts b/engine/system/processPhysics.ts
index 2ad4565..5a1b749 100644
--- a/engine/system/processPhysics.ts
+++ b/engine/system/processPhysics.ts
@@ -1,4 +1,7 @@
 import type { Circle } from "#/engine/Circle.ts";
+import type MapProxy from "#/engine/lib/MapProxy.ts";
+import type { Polygon } from "#/engine/Polygon.ts";
+import type { Rect } from "#/engine/Rect.ts";
 import $ from "#/engine/Scene.ts";
 import type { Vector } from "#/engine/Vector.ts";
 
@@ -8,26 +11,51 @@ const POLYGON = 2;
 
 type Shape = 0 | 1 | 2;
 
-export type Collider<T> = {
+export type Collider = {
 	shape: Shape;
-	body: T;
 };
 
-export type Collision = {};
+export type Collision = {
+	id: string;
+};
 
-export function moveAndCollide<T>(
-	collider: Collider<T>,
+const collisions = new Map<string, Collision>();
+
+function check(
+	id: string,
+	collider: Collider,
+	position: Vector,
+	colliders: MapProxy<string, Collider>,
+): string | undefined {
+	for (const [oid, other] of colliders.entries()) {
+		if (oid !== id && other) {
+			return oid;
+		}
+	}
+}
+
+export function moveAndCollide(
+	id: string,
 	velocity: Vector,
 	delta: number,
-): Collision {
-	return {};
+): Collision | undefined {
+	return collisions.get(id);
 }
 
 export function processPhysics(
 	ctx: CanvasRenderingContext2D,
 	delta: number,
 ): void {
-	for (const [id, collider] of $<Collider<unknown>>("collider")!.entries()) {
-		const position = $<Vector>("position")!.get(id);
+	const colliders = $<Collider>("collider")!;
+	const positions = $<Vector>("position")!;
+
+	for (const [id, collider] of colliders.entries()) {
+		const position = positions.get(id)!;
+		const target = check(id, collider.value, position.value, colliders);
+		if (target !== undefined) {
+			collisions.set(id, { id: target });
+		} else {
+			collisions.delete(id);
+		}
 	}
 }
diff --git a/game/entities/hero/entity.ts b/game/entities/hero/entity.ts
index 0e8e021..64e8379 100644
--- a/game/entities/hero/entity.ts
+++ b/game/entities/hero/entity.ts
@@ -29,7 +29,6 @@ const process = defineEntity("hero", {
 process((id, delta) => {
 	const position = $<Vector>("position").get(id)!.value;
 	const velocity = $<Vector>("velocity").get(id)!.value;
-	const collider = $<Collider>("collider").get(id)!.value;
 
 	if (pointer.isDown) {
 		position.x = pointer.position.x;
@@ -47,6 +46,6 @@ process((id, delta) => {
 	velocity.x = 0;
 	velocity.y = 0;
 
-	const collision = moveAndCollide(collider, velocity, delta);
-	console.log(collision);
+	const collision = moveAndCollide(id, velocity, delta);
+	// console.log(collision);
 });
diff --git a/game/entities/portal/entity.ts b/game/entities/portal/entity.ts
index c811ee9..83f6feb 100644
--- a/game/entities/portal/entity.ts
+++ b/game/entities/portal/entity.ts
@@ -1,3 +1,4 @@
+import { createCircle } from "#/engine/Circle.ts";
 import { defineEntity } from "#/engine/Entity.ts";
 import {
 	createSprite,
@@ -13,4 +14,5 @@ defineEntity("portal", {
 	position: createVector(),
 	sprite: createSprite(portalSrc),
 	animation: createSpriteAnimation(400, 0),
+	collider: createCircle(createVector(), 8),
 });