allow Vector2D scaling

ui/src/components/rects/rectangles.ts

@@ -10,9 +10,14 @@ export class Vector2D {
   public plus(other: Vector2D): Vector2D {
     return new Vector2D(this.x + other.x, this.y + other.y);
   }
+
   public minus(other: Vector2D): Vector2D {
     return new Vector2D(this.x - other.x, this.y - other.y);
   }
+
+  public scale(other: number): Vector2D {
+    return new Vector2D(this.x * other, this.y * other);
+  }
 }
 
 export class Rectangle {

ui/tests/unit/rectangle.spec.ts

@@ -20,6 +20,12 @@ describe("Vector2D Tests", () => {
     expect(v2.x).to.equal(-2);
     expect(v2.y).to.equal(-2);
   });
+
+  it("should scale vectors", () => {
+    const v2 = v.scale(3);
+    expect(v2.x).to.equal(3);
+    expect(v2.y).to.equal(6);
+  });
 });
 
 describe("Rectangle Tests", () => {