time for a snapshot

workshop/steps/07-swept-aabb/given.ts

@@ -0,0 +1,54 @@
+// Finished in earlier steps — reuse, don't rewrite.
+export type Vec = { x: number; y: number };
+export const vec = (x: number, y: number): Vec => ({ x, y });
+
+export type AABB = { x: number; y: number; w: number; h: number };
+export type Span = { entry: number; exit: number };
+export type Hit = { time: number; normal: Vec };
+
+/** Step 05, finished. */
+export function sweepInterval(
+	p: number,
+	v: number,
+	min: number,
+	max: number,
+): Span | null {
+	if (v === 0) {
+		return min <= p && p <= max
+			? { entry: -Infinity, exit: Infinity }
+			: null;
+	}
+
+	let t1 = (min - p) / v;
+	let t2 = (max - p) / v;
+	if (t1 > t2) {
+		[t1, t2] = [t2, t1];
+	}
+
+	return { entry: t1, exit: t2 };
+}
+
+/** Step 06, finished. A moving point vs a static box. */
+export function rayVsAABB(p: Vec, v: Vec, box: AABB): Hit | null {
+	const spanX = sweepInterval(p.x, v.x, box.x, box.x + box.w);
+	const spanY = sweepInterval(p.y, v.y, box.y, box.y + box.h);
+	if (spanX === null || spanY === null) {
+		return null;
+	}
+
+	const entry = Math.max(spanX.entry, spanY.entry);
+	const exit = Math.min(spanX.exit, spanY.exit);
+	if (entry > exit) {
+		return null;
+	}
+	if (entry >= 1 || exit <= 0) {
+		return null;
+	}
+
+	const normal =
+		spanX.entry > spanY.entry
+			? { x: v.x > 0 ? -1 : 1, y: 0 }
+			: { x: 0, y: v.y > 0 ? -1 : 1 };
+
+	return { time: entry, normal };
+}