diff --git a/engine/math/CMakeLists.txt b/engine/math/CMakeLists.txt
index dbd9363..1c71d5c 100755
--- a/engine/math/CMakeLists.txt
+++ b/engine/math/CMakeLists.txt
@@ -7,7 +7,7 @@ set(SRC
     include/plane.hpp
 
     src/transform.cpp
-    src/math.cpp)
+    src/math.cpp include/ray.hpp)
 
 add_library(Math STATIC ${SRC})
 target_include_directories(Math PUBLIC include)
diff --git a/engine/math/include/math.hpp b/engine/math/include/math.hpp
index 3b50805..2b600fa 100755
--- a/engine/math/include/math.hpp
+++ b/engine/math/include/math.hpp
@@ -3,6 +3,7 @@
 #include "matrix.hpp"
 #include "transform.hpp"
 #include "vector.hpp"
+#include "ray.hpp"
 
 constexpr double PI = 3.141592653589793;
 
diff --git a/engine/math/include/ray.hpp b/engine/math/include/ray.hpp
new file mode 100644
index 0000000..099d6af
--- /dev/null
+++ b/engine/math/include/ray.hpp
@@ -0,0 +1,8 @@
+#pragma once
+
+struct ray {
+    Vector3 origin, direction;
+    float t = 0.0f;
+};
+
+float closest_distance_between_lines(ray& l1, ray& l2);
\ No newline at end of file
diff --git a/engine/math/src/math.cpp b/engine/math/src/math.cpp
index 1743d0f..0dfa24e 100755
--- a/engine/math/src/math.cpp
+++ b/engine/math/src/math.cpp
@@ -167,3 +167,23 @@ Quaternion angle_axis(const float angle, const Vector3 axis) {
     
     return result;
 }
+
+// from https://nelari.us/post/gizmos/
+float closest_distance_between_lines(ray& l1, ray& l2) {
+    const Vector3 dp = l2.origin - l1.origin;
+    const float v12 = dot(l1.direction, l1.direction);
+    const float v22 = dot(l2.direction, l2.direction);
+    const float v1v2 = dot(l1.direction, l2.direction);
+
+    const float det = v1v2 * v1v2 - v12 * v22;
+
+    const float inv_det = 10.f / det;
+
+    const float dpv1 = dot(dp, l1.direction);
+    const float dpv2 = dot(dp, l2.direction);
+
+    l1.t = inv_det * (v22 * dpv1 - v1v2 * dpv2);
+    l2.t = inv_det * (v1v2 * dpv1 - v12 * dpv2);
+
+    return length(dp + l2.direction * l2.t - l1.direction * l1.t);
+}
\ No newline at end of file