1 files changed, 97 insertions, 0 deletions
diff --git a/engine/components/BoundingBox.ts b/engine/components/BoundingBox.ts
new file mode 100644
index 0000000..2b1d648
--- /dev/null
+++ b/engine/components/BoundingBox.ts
@@ -0,0 +1,97 @@
+import { Component, ComponentNames } from ".";
+import type { Coord2D, Dimension2D } from "../interfaces";
+import { dotProduct, rotateVector, normalizeVector } from "../utils";
+
+export class BoundingBox extends Component {
+  public center: Coord2D;
+  public dimension: Dimension2D;
+  public rotation: number;
+
+  constructor(center: Coord2D, dimension: Dimension2D, rotation?: number) {
+    super(ComponentNames.BoundingBox);
+
+    this.center = center;
+    this.dimension = dimension;
+    this.rotation = rotation ?? 0;
+  }
+
+  public isCollidingWith(box: BoundingBox): boolean {
+    const boxes = [this.getVertices(), box.getVertices()];
+    for (const poly of boxes) {
+      for (let i = 0; i < poly.length; ++i) {
+        const [A, B] = [poly[i], poly[(i + 1) % poly.length]];
+        const normal: Coord2D = { x: B.y - A.y, y: A.x - B.x };
+
+        const [[minThis, maxThis], [minBox, maxBox]] = boxes.map((box) =>
+          box.reduce(
+            ([min, max], vertex) => {
+              const projection = dotProduct(normal, vertex);
+              return [Math.min(min, projection), Math.max(max, projection)];
+            },
+            [Infinity, -Infinity]
+          )
+        );
+
+        if (maxThis < minBox || maxBox < minThis) return false;
+      }
+    }
+
+    return true;
+  }
+
+  public getVertices(): Coord2D[] {
+    return [
+      { x: -this.dimension.width / 2, y: -this.dimension.height / 2 },
+      { x: -this.dimension.width / 2, y: this.dimension.height / 2 },
+      { x: this.dimension.width / 2, y: this.dimension.height / 2 },
+      { x: this.dimension.width / 2, y: -this.dimension.height / 2 },
+    ]
+      .map((vertex) => rotateVector(vertex, this.rotation))
+      .map((vertex) => {
+        return {
+          x: vertex.x + this.center.x,
+          y: vertex.y + this.center.y,
+        };
+      });
+  }
+
+  private getAxes() {
+    const corners: Coord2D[] = this.getVerticesRelativeToCenter();
+    const axes: Coord2D[] = [];
+
+    for (let i = 0; i < corners.length; ++i) {
+      const [cornerA, cornerB] = [
+        corners[i],
+        corners[(i + 1) % corners.length],
+      ].map((corner) => rotateVector(corner, this.rotation));
+
+      axes.push(
+        normalizeVector({
+          x: cornerB.y - cornerA.y,
+          y: -(cornerB.x - cornerA.x),
+        })
+      );
+    }
+
+    return axes;
+  }
+
+  private project(axis: Coord2D): [number, number] {
+    const corners = this.getCornersRelativeToCenter();
+    let [min, max] = [Infinity, -Infinity];
+
+    for (const corner of corners) {
+      const rotated = rotateVector(corner, this.rotation);
+      const translated = {
+        x: rotated.x + this.center.x,
+        y: rotated.y + this.center.y,
+      };
+      const projection = dotProduct(translated, axis);
+
+      min = Math.min(projection, min);
+      max = Math.max(projection, max);
+    }
+
+    return [min, max];
+  }
+}