1 files changed, 38 insertions, 0 deletions
diff --git a/packages/math/line.ts b/packages/math/line.ts
new file mode 100644
index 0000000..bcb4f6d
--- /dev/null
+++ b/packages/math/line.ts
@@ -0,0 +1,38 @@
+import { pointFrom } from "./point";
+import type { GlobalPoint, Line, LocalPoint } from "./types";
+
+/**
+ * Create a line from two points.
+ *
+ * @param points The two points lying on the line
+ * @returns The line on which the points lie
+ */
+export function line<P extends GlobalPoint | LocalPoint>(a: P, b: P): Line<P> {
+  return [a, b] as Line<P>;
+}
+
+/**
+ * Determines the intersection point (unless the lines are parallel) of two
+ * lines
+ *
+ * @param a
+ * @param b
+ * @returns
+ */
+export function linesIntersectAt<Point extends GlobalPoint | LocalPoint>(
+  a: Line<Point>,
+  b: Line<Point>,
+): Point | null {
+  const A1 = a[1][1] - a[0][1];
+  const B1 = a[0][0] - a[1][0];
+  const A2 = b[1][1] - b[0][1];
+  const B2 = b[0][0] - b[1][0];
+  const D = A1 * B2 - A2 * B1;
+  if (D !== 0) {
+    const C1 = A1 * a[0][0] + B1 * a[0][1];
+    const C2 = A2 * b[0][0] + B2 * b[0][1];
+    return pointFrom<Point>((C1 * B2 - C2 * B1) / D, (A1 * C2 - A2 * C1) / D);
+  }
+
+  return null;
+}