From 98d5b9b417d585a2d0baf4a28c7b2dd3fe7b4b35 Mon Sep 17 00:00:00 2001
From: Ben Cragg <bcvery1@gmail.com>
Date: Wed, 3 Apr 2019 12:12:27 +0100
Subject: [PATCH] Adding vertical/horizontal edge cases

---
 geometry.go | 39 ++++++++++++++++++++++++++++++---------
 1 file changed, 30 insertions(+), 9 deletions(-)

diff --git a/geometry.go b/geometry.go
index 4f4c1e4..73f4854 100644
--- a/geometry.go
+++ b/geometry.go
@@ -206,20 +206,48 @@ func (l Line) Center() Vec {
 
 // Closest will return the point on the line which is closest to the `Vec` provided.
 func (l Line) Closest(v Vec) Vec {
-	// Closest point will be on a line, perpendicular to this line
+	// between is a helper function which determines whether 'x' is greater than min(a, b) and less than max(a, b)
+	between := func(a, b, x float64) bool {
+		min := math.Min(a, b)
+		max := math.Max(a, b)
+		return min < x && x < max
+	}
+
+	// Closest point will be on a line which perpendicular to this line.
+	// If and only if the infinite perpendicular line intersects the segment.
 	m, b := l.Formula()
 
 	// Account for horizontal lines
 	if m == 0 {
 		x := v.X
 		y := l.A.Y
-		return V(x, y)
+
+		// check if the X coordinate of v is on the line
+		if between(l.A.X, l.B.X, v.X) {
+			return V(x, y)
+		}
+
+		// Otherwise get the closest endpoint
+		if l.A.To(v).Len() < l.B.To(v).Len() {
+			return l.A
+		}
+		return l.B
 	}
 
 	// Account for vertical lines
 	if math.IsInf(math.Abs(m), 1) {
 		x := l.A.X
 		y := v.Y
+
+		// check if the Y coordinate of v is on the line
+		if between(l.A.Y, l.B.Y, v.Y) {
+			return V(x, y)
+		}
+
+		// Otherwise get the closest endpoint
+		if l.A.To(v).Len() < l.B.To(v).Len() {
+			return l.A
+		}
 		return V(x, y)
 	}
 
@@ -230,13 +258,6 @@ func (l Line) Closest(v Vec) Vec {
 	x := (perpendicularB - b) / (m - perpendicularM)
 	y := m*x + b
 
-	// between is a helper function which determines whether 'x' is greater than min(a, b) and less than max(a, b)
-	between := func(a, b, x float64) bool {
-		min := math.Min(a, b)
-		max := math.Max(a, b)
-		return min < x && x < max
-	}
-
 	// Check if the point lies between the x and y bounds of the segment
 	if !between(l.A.X, l.B.X, x) && !between(l.A.Y, l.B.Y, y) {
 		// Not within bounding box