From a077f669ee5409c7550df538dd00c6b294d7019f Mon Sep 17 00:00:00 2001
From: Vojtech Bubnik <bubnikv@gmail.com>
Date: Tue, 2 May 2023 16:32:03 +0200
Subject: [PATCH] Slight optimization of distance_to_squared()

---
 src/libslic3r/Line.hpp | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/src/libslic3r/Line.hpp b/src/libslic3r/Line.hpp
index 1edd1f5e9..d90757bed 100644
--- a/src/libslic3r/Line.hpp
+++ b/src/libslic3r/Line.hpp
@@ -40,11 +40,12 @@ template<class L> auto get_b(L &&l) { return Traits<remove_cvref_t<L>>::get_b(l)
 
 // Distance to the closest point of line.
 template<class L>
-double distance_to_squared(const L &line, const Vec<Dim<L>, Scalar<L>> &point, Vec<Dim<L>, Scalar<L>> *nearest_point)
+inline double distance_to_squared(const L &line, const Vec<Dim<L>, Scalar<L>> &point, Vec<Dim<L>, Scalar<L>> *nearest_point)
 {
-    const Vec<Dim<L>, double>  v  = (get_b(line) - get_a(line)).template cast<double>();
-    const Vec<Dim<L>, double>  va = (point  - get_a(line)).template cast<double>();
-    const double  l2 = v.squaredNorm();  // avoid a sqrt
+    using VecType = Vec<Dim<L>, double>;
+    const VecType  v  = (get_b(line) - get_a(line)).template cast<double>();
+    const VecType  va = (point  - get_a(line)).template cast<double>();
+    const double  l2 = v.squaredNorm();
     if (l2 == 0.0) {
         // a == b case
         *nearest_point = get_a(line);
@@ -53,19 +54,20 @@ double distance_to_squared(const L &line, const Vec<Dim<L>, Scalar<L>> &point, V
     // Consider the line extending the segment, parameterized as a + t (b - a).
     // We find projection of this point onto the line.
     // It falls where t = [(this-a) . (b-a)] / |b-a|^2
-    const double t = va.dot(v) / l2;
+    const double t = va.dot(v);
     if (t <= 0.0) {
         // beyond the 'a' end of the segment
         *nearest_point = get_a(line);
         return va.squaredNorm();
-    } else if (t >= 1.0) {
+    } else if (t >= l2) {
         // beyond the 'b' end of the segment
         *nearest_point = get_b(line);
         return (point - get_b(line)).template cast<double>().squaredNorm();
     }
 
-    *nearest_point = (get_a(line).template cast<double>() + t * v).template cast<Scalar<L>>();
-    return (t * v - va).squaredNorm();
+    const VecType w = ((t / l2) * v).eval();
+    *nearest_point = (get_a(line).template cast<double>() + w).template cast<Scalar<L>>();
+    return (w - va).squaredNorm();
 }
 
 // Distance to the closest point of line.