WIP

engine/Polygon.ts

@@ -1,7 +1,48 @@
-import type { Vector } from "#/engine/Vector.ts";
+import { createVector, type Vector } from "#/engine/Vector.ts";
 
 export type Polygon = {
 	position: Vector;
 	points: Array<Vector>;
 	axes: Array<Vector>;
 };
+
+export function createPolygon(
+	position: Vector,
+	points: Array<Vector>,
+): Polygon {
+	const axes = points.map(() => createVector());
+	const polygon = { position, points, axes };
+	updateAxes(polygon);
+
+	return polygon;
+}
+
+export function updateAxes({ points, axes }: Polygon): void {
+	const cap = axes.length - 1;
+	const p0 = points[0];
+	let pi = p0;
+
+	for (let i = 0; i < cap; i++) {
+		const pj = points[i + 1];
+
+		const nx = -(pj.y - pi.y);
+		const ny = pj.x - pi.x;
+
+		const invLen = 1.0 / Math.sqrt(nx * nx + ny * ny);
+
+		const axis = axes[i];
+		axis.x = nx * invLen;
+		axis.y = ny * invLen;
+
+		pi = pj;
+	}
+
+	const nx = -(p0.y - pi.y);
+	const ny = p0.x - pi.x;
+
+	const invLen = 1.0 / Math.sqrt(nx * nx + ny * ny);
+
+	const axis = axes[cap];
+	axis.x = nx * invLen;
+	axis.y = ny * invLen;
+}