From 4057a131c83385e967e38a273d9c52c7dbca5505 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Thu, 19 Feb 2015 14:20:09 +1100
Subject: [PATCH] line: add closest parameter to point query

---
 line.cpp | 17 ++++++++++++++---
 line.hpp |  1 +
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/line.cpp b/line.cpp
index 90e66883..c1c84a00 100644
--- a/line.cpp
+++ b/line.cpp
@@ -34,15 +34,26 @@ util::line<S,T>::line (util::point<S,T> _p,
 
 
 ///----------------------------------------------------------------------------
-/// returns the distance alone the line in a line-plane intersection
+/// returns the distance along the line in a line-plane intersection
 ///
 /// returns inf if parallel
 /// returns 0   if colinear
 template <size_t S, typename T>
 T
-util::line<S,T>::intersect (plane<S,T> rhs) const
+util::line<S,T>::intersect (plane<S,T> q) const
 {
-    return dot (rhs.p - p, rhs.n) / dot (d, rhs.n);
+    return dot (q.p - p, q.n) / dot (d, q.n);
+}
+
+
+///----------------------------------------------------------------------------
+/// returns the closest parameter along the line to a given point
+template <size_t S, typename T>
+T
+util::line<S,T>::closest (point<S,T> q) const
+{
+    // project the origin-point difference onto the direction
+    return dot (p - q, d);
 }
 
 
diff --git a/line.hpp b/line.hpp
index 3a13b94a..1b5d017d 100644
--- a/line.hpp
+++ b/line.hpp
@@ -31,6 +31,7 @@ namespace util {
               util::vector<S,T> direction);
 
         T intersect (plane<S,T>) const;
+        T closest (point<S,T>) const;
 
         util::point<S,T> at (T) const;