time for a snapshot

workshop/steps/05-sweep-1d/sweep1d.ts

@@ -0,0 +1,42 @@
+export type Span = { entry: number; exit: number };
+
+/**
+ * When is a point at `p`, moving by `v` over the frame, inside [min, max]?
+ *
+ * Returns the entry/exit times (t, where the position is p + v*t).
+ * `entry` is always <= `exit`. Values may be < 0 or > 1.
+ *
+ * Special case: if v === 0, return {entry:-Infinity, exit:Infinity} when the
+ * point is already inside [min, max], otherwise return null.
+ */
+export function sweepInterval(
+	p: number,
+	v: number,
+	min: number,
+	max: number,
+): Span | null {
+	if (v === 0) {
+		return isInBetween(p, min, 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,
+	};
+}
+
+function isInBetween(p: number, min: number, max: number): boolean {
+	return min <= p && p <= max;
+}