6 files changed, 91 insertions, 8 deletions
diff --git a/src/engine/components/Colliding.ts b/src/engine/components/Colliding.ts
new file mode 100644
index 0000000..fe782df
--- /dev/null
+++ b/src/engine/components/Colliding.ts
@@ -0,0 +1,13 @@
+import { Component, ComponentNames } from ".";
+import { Game } from "..";
+import { Entity } from "../entities";
+
+export class Colliding extends Component {
+  public onCollision?: (game: Game, entity: Entity) => void;
+
+  constructor(onCollision?: (game: Game, entity: Entity) => void) {
+    super(ComponentNames.Colliding);
+
+    this.onCollision = onCollision;
+  }
+}
diff --git a/src/engine/components/ComponentNames.ts b/src/engine/components/ComponentNames.ts
index fdf1a18..aec14c5 100644
--- a/src/engine/components/ComponentNames.ts
+++ b/src/engine/components/ComponentNames.ts
@@ -7,6 +7,7 @@ export namespace ComponentNames {
   export const Highlight = "Highlight";
   export const Interactable = "Interactable";
   export const Pushable = "Pushable";
+  export const Colliding = "Colliding";
   export const RadialObserve = "RadialObserve";
   export const GridSpawn = "GridSpawn";
   export const Text = "Text";
diff --git a/src/engine/components/RadialObserver.ts b/src/engine/components/RadialObserver.ts
new file mode 100644
index 0000000..627c4ff
--- /dev/null
+++ b/src/engine/components/RadialObserver.ts
@@ -0,0 +1,13 @@
+import { Component, ComponentNames } from ".";
+import { Game } from "..";
+import { Entity } from "../entities";
+
+export class Colliding extends Component {
+  public onCollision?: (game: Game, entity: Entity) => void;
+
+  constructor(onCollision?: (game: Game, entity: Entity) => void) {
+    super(ComponentNames.RadialObserve);
+
+    this.onCollision = onCollision;
+  }
+}
diff --git a/src/engine/components/index.ts b/src/engine/components/index.ts
index d3b2fd0..0e5f85c 100644
--- a/src/engine/components/index.ts
+++ b/src/engine/components/index.ts
@@ -8,6 +8,7 @@ export * from "./Control";
 export * from "./Highlight";
 export * from "./Interactable";
 export * from "./Pushable";
+export * from "./RadialObserve";
 export * from "./Colliding";
 export * from "./GridSpawn";
 export * from "./Text";
diff --git a/src/engine/interfaces/Vec2.ts b/src/engine/interfaces/Vec2.ts
index 04be4be..cdb150e 100644
--- a/src/engine/interfaces/Vec2.ts
+++ b/src/engine/interfaces/Vec2.ts
@@ -2,6 +2,8 @@ export interface Coord2D {
   x: number;
   y: number;
 }
+export const cartesianDistance = (a: Coord2D, b: Coord2D) =>
+  Math.sqrt((b.y - a.y) ** 2 + (b.x - a.x) ** 2);
 
 export interface Dimension2D {
   width: number;
@@ -15,11 +17,3 @@ export interface Velocity2D {
   };
   dTheta: number;
 }
-
-export interface Force2D {
-  fCartesian: {
-    fx: number;
-    fy: number;
-  };
-  torque: number;
-}
diff --git a/src/engine/systems/RadialObserve.ts b/src/engine/systems/RadialObserve.ts
new file mode 100644
index 0000000..8d418df
--- /dev/null
+++ b/src/engine/systems/RadialObserve.ts
@@ -0,0 +1,61 @@
+import { System, SystemNames } from ".";
+import { ComponentNames, Grid, RadialObserve } from "../components";
+import { Entity, EntityNames } from "../entities";
+import { Game } from "../Game";
+import { cartesianDistance } from "../interfaces";
+
+const radialObservations: Record<string, Set<string>> = {
+  TODO: new Set([]),
+};
+
+export class RadialObserver extends System {
+  constructor() {
+    super(SystemNames.RadialObserver);
+  }
+
+  public update(_dt: number, game: Game) {
+    game.forEachEntityWithComponent(ComponentNames.RadialObserve, (entity) => {
+      if (!(entity.name in radialObservations)) {
+        return;
+      }
+      const observable = radialObservations[entity.name];
+
+      const entityObserve = entity.getComponent<RadialObserve>(
+        ComponentNames.RadialObserve,
+      );
+      if (!entityObserve.onObservation) {
+	return;
+      }
+
+      const entityPosition = entity.getComponent<Grid>(
+        ComponentNames.Grid,
+      ).gridPosition;
+
+      const observations: Entity[] = [];
+      game.forEachEntityWithComponent(ComponentNames.RadialObserve, (other) => {
+        if (entity === other) {
+          return;
+        }
+        if (!observable.has(other.name)) {
+          return;
+        }
+
+        const otherPosition = other.getComponent<Grid>(
+          ComponentNames.Grid,
+        ).gridPosition;
+        if (
+          cartesianDistance(entityPosition, otherPosition) >
+          entityObserve.radius
+        ) {
+          return;
+        }
+
+        observations.push(other);
+      });
+
+      for (const observation of observations) {
+	entityObserve.onObservation!(game, observation);
+      }
+    });
+  }
+}