From a66e5c6dabd745738b4184583400bc757e2b97a4 Mon Sep 17 00:00:00 2001
From: Sam Hocevar <sam@hocevar.net>
Date: Sat, 17 May 2014 12:09:56 +0000
Subject: [PATCH] geometry: implement point-to-segment distance function.

---
 src/lol/math/geometry.h | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/src/lol/math/geometry.h b/src/lol/math/geometry.h
index 1636a0d7..05cf712b 100644
--- a/src/lol/math/geometry.h
+++ b/src/lol/math/geometry.h
@@ -314,24 +314,34 @@ PlaneIntersection TestPointVsPlane(const TV &point, const TV &plane_p, const TV
         return PlaneIntersection::Plane;
 }
 
-//Project points functions
-//Plane
+/* Project point on plane */
 template <typename TV>
-TV ProjectPointOnPlane(TV const &proj_point, TV const &plane_point, TV const &plane_normal)
+TV ProjectPointOnPlane(TV const &p, TV const &origin, TV const &normal)
 {
-    return proj_point - dot(proj_point - plane_point, plane_normal) * plane_normal;
+    return p - dot(p - origin, normal) * normal;
 }
-//Line
+
+/* Project point on line */
+template <typename TV>
+TV ProjectPointOnRay(TV const &p, TV const &origin, TV const &direction)
+{
+    return origin + direction * dot(p - origin, direction);
+}
+
+/* Distance from point to plane */
 template <typename TV>
-TV ProjectPointOnRay(TV const &proj_point, TV const &ray_point, TV const &ray_dir)
+float PointDistToPlane(TV const &p, TV const &origin, TV const &normal)
 {
-    return ray_point + ray_dir * dot(proj_point - ray_point, ray_dir);
+    return abs(dot(p - origin, normal));
 }
-//Point dist to plane
+
+/* Distance from point to segment */
 template <typename TV>
-float PointDistToPlane(TV const &proj_point, TV const &plane_point, TV const &plane_normal)
+float PointDistToSegment(TV const &p, TV const &a, TV const &b)
 {
-    return abs(dot(proj_point - plane_point, plane_normal));
+    float d2 = sqlength(b - a);
+    float u = d2 ? dot(p - a, b - a) / d2 : 0.0f;
+    return distance(p, mix(a, b, clamp(u, 0.0f, 1.0f)));
 }
 
 } /* namespace lol */