From e939cca6fdb9d86f4807d18bc96783c1819fd275 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Wed, 15 Apr 2015 14:20:59 +1000
Subject: [PATCH] ray: return NaN for negative aabb intersection

---
 ray.cpp      |  7 +++++--
 test/ray.cpp | 13 ++++++++++---
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/ray.cpp b/ray.cpp
index 1910fbfa..7b37b9ab 100644
--- a/ray.cpp
+++ b/ray.cpp
@@ -47,7 +47,7 @@ util::ray<S,T>::intersect (plane<S,T> q) const
 /// returns the distance from origin to AABB intersection
 ///
 /// returns NaN on miss
-/// returns -ve if behind
+/// returns NaN if behind
 template <size_t S, typename T>
 T
 util::ray<S,T>::intersect (AABB<S,T> r) const
@@ -61,9 +61,11 @@ util::ray<S,T>::intersect (AABB<S,T> r) const
     auto tmin = max (vmin);
     auto tmax = min (vmax);
 
+    // closest intersection is behind us
     if (tmax < 0)
-        return tmax;
+        return std::numeric_limits<T>::quiet_NaN ();
 
+    // missed intersection
     if (tmin > tmax)
         return std::numeric_limits<T>::quiet_NaN ();
 
@@ -75,6 +77,7 @@ util::ray<S,T>::intersect (AABB<S,T> r) const
 /// returns the smallest distance from ray origin to a sphere intersection
 ///
 /// returns NaN on miss
+/// returns NaN if behind
 template <size_t S, typename T>
 T
 util::ray<S,T>::intersect (sphere<S,T> s) const
diff --git a/test/ray.cpp b/test/ray.cpp
index a42ebeab..f3da84c2 100644
--- a/test/ray.cpp
+++ b/test/ray.cpp
@@ -22,17 +22,24 @@ void
 test_intersect_aabb (util::TAP::logger &tap)
 {
     // trivial case: unit aabb at origin, ray from (0.5,-0.5) upwards
-    const util::AABB2f b {
+    const util::AABB2f box {
         { 0.f, 0.f },
         { 1.f, 1.f }
     };
 
-    const util::ray2f l {
+    const util::ray2f forward {
         { 0.5f, -0.5f },
         { 0.f,   1.f }
     };
 
-    tap.expect_eq (l.intersect (b), 0.5f, "ray-aabb intersect");
+    tap.expect_eq (forward.intersect (box), 0.5f, "ray-aabb intersect");
+
+    const util::ray2f behind {
+        { 0.5f, 2.f },
+        { 0.f, 1.f }
+    };
+
+    tap.expect_nan (behind.intersect (box), "ray-aabb intersect behind");
 }