1 files changed, 122 insertions, 0 deletions
diff --git a/src/engine/components/BoundingBox.ts b/src/engine/components/BoundingBox.ts
new file mode 100644
index 0000000..d64041f
--- /dev/null
+++ b/src/engine/components/BoundingBox.ts
@@ -0,0 +1,122 @@
+import { Component, ComponentNames } from ".";
+import type { Coord2D, Dimension2D } from "../interfaces";
+import { dotProduct, rotateVector } 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 {
+    // optimization; when neither rotates just check if they overlap
+    if (this.rotation == 0 && box.rotation == 0) {
+      const thisTopLeft = this.getTopLeft();
+      const thisBottomRight = this.getBottomRight();
+
+      const thatTopLeft = box.getTopLeft();
+      const thatBottomRight = box.getBottomRight();
+
+      if (
+        thisBottomRight.x <= thatTopLeft.x ||
+        thisTopLeft.x >= thatBottomRight.x ||
+        thisBottomRight.y <= thatTopLeft.y ||
+        thisTopLeft.y >= thatBottomRight.y
+      ) {
+        return false;
+      }
+
+      return true;
+    }
+
+    // https://en.wikipedia.org/wiki/Hyperplane_separation_theorem
+    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)) // rotate
+      .map((vertex) => {
+        // translate
+        return {
+          x: vertex.x + this.center.x,
+          y: vertex.y + this.center.y,
+        };
+      });
+  }
+
+  public getRotationInPiOfUnitCircle(): number {
+    let rads = this.rotation * (Math.PI / 180);
+    if (rads >= Math.PI) {
+      // Physics system guarantees rotation \in [0, 360)
+      rads -= Math.PI;
+    }
+    return rads;
+  }
+
+  public getOutscribedBoxDims(): Dimension2D {
+    let rads = this.getRotationInPiOfUnitCircle();
+    const { width, height } = this.dimension;
+
+    if (rads == 0) return this.dimension;
+
+    if (rads <= Math.PI / 2) {
+      return {
+        width: Math.abs(height * Math.sin(rads) + width * Math.cos(rads)),
+        height: Math.abs(width * Math.sin(rads) + height * Math.cos(rads)),
+      };
+    }
+
+    rads -= Math.PI / 2;
+    return {
+      width: Math.abs(height * Math.cos(rads) + width * Math.sin(rads)),
+      height: Math.abs(width * Math.cos(rads) + height * Math.sin(rads)),
+    };
+  }
+
+  public getTopLeft(): Coord2D {
+    return {
+      x: this.center.x - this.dimension.width / 2,
+      y: this.center.y - this.dimension.height / 2,
+    };
+  }
+
+  public getBottomRight(): Coord2D {
+    return {
+      x: this.center.x + this.dimension.width / 2,
+      y: this.center.y + this.dimension.height / 2,
+    };
+  }
+}