From 6ec259a0e71174651bae95d4628138bf6fd68742 Mon Sep 17 00:00:00 2001
From: kj_sh604
Date: Sun, 15 Mar 2026 16:19:35 -0400
Subject: refactor: packages/

---
 packages/utils/bbox.ts | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 packages/utils/bbox.ts

(limited to 'packages/utils/bbox.ts')

diff --git a/packages/utils/bbox.ts b/packages/utils/bbox.ts
new file mode 100644
index 0000000..19a1a54
--- /dev/null
+++ b/packages/utils/bbox.ts
@@ -0,0 +1,72 @@
+import {
+  vectorCross,
+  vectorFromPoint,
+  type GlobalPoint,
+  type LocalPoint,
+} from "@excalidraw/math";
+import type { Bounds } from "@excalidraw/excalidraw/element/bounds";
+
+export type LineSegment<P extends LocalPoint | GlobalPoint> = [P, P];
+
+export function getBBox<P extends LocalPoint | GlobalPoint>(
+  line: LineSegment<P>,
+): Bounds {
+  return [
+    Math.min(line[0][0], line[1][0]),
+    Math.min(line[0][1], line[1][1]),
+    Math.max(line[0][0], line[1][0]),
+    Math.max(line[0][1], line[1][1]),
+  ];
+}
+
+export function doBBoxesIntersect(a: Bounds, b: Bounds) {
+  return a[0] <= b[2] && a[2] >= b[0] && a[1] <= b[3] && a[3] >= b[1];
+}
+
+const EPSILON = 0.000001;
+
+export function isPointOnLine<P extends GlobalPoint | LocalPoint>(
+  l: LineSegment<P>,
+  p: P,
+) {
+  const p1 = vectorFromPoint(l[1], l[0]);
+  const p2 = vectorFromPoint(p, l[0]);
+
+  const r = vectorCross(p1, p2);
+
+  return Math.abs(r) < EPSILON;
+}
+
+export function isPointRightOfLine<P extends GlobalPoint | LocalPoint>(
+  l: LineSegment<P>,
+  p: P,
+) {
+  const p1 = vectorFromPoint(l[1], l[0]);
+  const p2 = vectorFromPoint(p, l[0]);
+
+  return vectorCross(p1, p2) < 0;
+}
+
+export function isLineSegmentTouchingOrCrossingLine<
+  P extends GlobalPoint | LocalPoint,
+>(a: LineSegment<P>, b: LineSegment<P>) {
+  return (
+    isPointOnLine(a, b[0]) ||
+    isPointOnLine(a, b[1]) ||
+    (isPointRightOfLine(a, b[0])
+      ? !isPointRightOfLine(a, b[1])
+      : isPointRightOfLine(a, b[1]))
+  );
+}
+
+// https://martin-thoma.com/how-to-check-if-two-line-segments-intersect/
+export function doLineSegmentsIntersect<P extends GlobalPoint | LocalPoint>(
+  a: LineSegment<P>,
+  b: LineSegment<P>,
+) {
+  return (
+    doBBoxesIntersect(getBBox(a), getBBox(b)) &&
+    isLineSegmentTouchingOrCrossingLine(a, b) &&
+    isLineSegmentTouchingOrCrossingLine(b, a)
+  );
+}
-- 
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