From c2bf905f4b9863fe0f5c876ed00fe298cb95ab6b Mon Sep 17 00:00:00 2001
From: Daniel Karbach <daniel.karbach@localhorst.tv>
Date: Mon, 14 Nov 2016 17:32:56 +0100
Subject: [PATCH] make Intersection() repeatable for normal

---
 src/geometry/geometry.cpp         |  8 +--
 tst/geometry/IntersectionTest.cpp | 95 ++++++++++++++++++++++++++++++-
 2 files changed, 97 insertions(+), 6 deletions(-)

diff --git a/src/geometry/geometry.cpp b/src/geometry/geometry.cpp
index 5db29c8..6ff26ca 100644
--- a/src/geometry/geometry.cpp
+++ b/src/geometry/geometry.cpp
@@ -109,14 +109,14 @@ bool Intersection(
 		glm::vec3 min_all(glm::min(t1, t2));
 		if (min_all.x > min_all.y) {
 			if (min_all.x > min_all.z) {
-				normal->x = t2.x < t1.x ? 1 : -1;
+				*normal = glm::vec3(t2.x < t1.x ? 1 : -1, 0, 0);
 			} else {
-				normal->z = t2.z < t1.z ? 1 : -1;
+				*normal = glm::vec3(0, 0, t2.z < t1.z ? 1 : -1);
 			}
 		} else if (min_all.y > min_all.z) {
-			normal->y = t2.y < t1.y ? 1 : -1;
+			*normal = glm::vec3(0, t2.y < t1.y ? 1 : -1, 0);
 		} else {
-			normal->z = t2.z < t1.z ? 1 : -1;
+			*normal = glm::vec3(0, 0, t2.z < t1.z ? 1 : -1);
 		}
 	}
 	return true;
diff --git a/tst/geometry/IntersectionTest.cpp b/tst/geometry/IntersectionTest.cpp
index 1b61838..04980c6 100644
--- a/tst/geometry/IntersectionTest.cpp
+++ b/tst/geometry/IntersectionTest.cpp
@@ -87,7 +87,7 @@ void IntersectionTest::testRayBoxIntersection() {
 	// should be 4 units to the left now
 	ray.orig.x = -5;
 	CPPUNIT_ASSERT_MESSAGE(
-		"ray pointing at box doesn't intersect",
+		"ray pointing at box to the right doesn't intersect",
 		Intersection(ray, box, M, &distance, &normal)
 	);
 	CPPUNIT_ASSERT_DOUBLES_EQUAL_MESSAGE(
@@ -102,10 +102,101 @@ void IntersectionTest::testRayBoxIntersection() {
 	// move ray to the other side, so it's pointing away now
 	ray.orig.x = 5;
 	CPPUNIT_ASSERT_MESSAGE(
-		"ray pointing away from box still intersects",
+		"ray pointing away from box to the left still intersects",
 		!Intersection(ray, box, M)
 	);
 
+	// turn ray around
+	ray.dir.x = -1;
+	CPPUNIT_ASSERT_MESSAGE(
+		"ray pointing at box to the left does not intersect",
+		Intersection(ray, box, M, &distance, &normal)
+	);
+	CPPUNIT_ASSERT_DOUBLES_EQUAL_MESSAGE(
+		"intersection distance way off",
+		4.0f, distance, delta
+	);
+	CPPUNIT_ASSERT_EQUAL_MESSAGE(
+		"wrong surface normal at intersection point",
+		glm::vec3(1, 0, 0), normal
+	);
+
+	// ray below
+	ray.orig = { 0, -5, 0 };
+	ray.dir = { 0, 1, 0 };
+	CPPUNIT_ASSERT_MESSAGE(
+		"ray pointing at box above does not intersect",
+		Intersection(ray, box, M, &distance, &normal)
+	);
+	CPPUNIT_ASSERT_DOUBLES_EQUAL_MESSAGE(
+		"intersection distance way off",
+		4.0f, distance, delta
+	);
+	CPPUNIT_ASSERT_EQUAL_MESSAGE(
+		"wrong surface normal at intersection point",
+		glm::vec3(0, -1, 0), normal
+	);
+
+	// turn ray around
+	ray.dir.y = -1;
+	CPPUNIT_ASSERT_MESSAGE(
+		"ray pointing away from box above still intersects",
+		!Intersection(ray, box, M)
+	);
+
+	// move ray above
+	ray.orig.y = 5;
+	CPPUNIT_ASSERT_MESSAGE(
+		"ray pointing at box below does not intersect",
+		Intersection(ray, box, M, &distance, &normal)
+	);
+	CPPUNIT_ASSERT_DOUBLES_EQUAL_MESSAGE(
+		"intersection distance way off",
+		4.0f, distance, delta
+	);
+	CPPUNIT_ASSERT_EQUAL_MESSAGE(
+		"wrong surface normal at intersection point",
+		glm::vec3(0, 1, 0), normal
+	);
+
+	// ray behind
+	ray.orig = { 0, 0, -5 };
+	ray.dir = { 0, 0, 1 };
+	CPPUNIT_ASSERT_MESSAGE(
+		"ray pointing at box in front does not intersect",
+		Intersection(ray, box, M, &distance, &normal)
+	);
+	CPPUNIT_ASSERT_DOUBLES_EQUAL_MESSAGE(
+		"intersection distance way off",
+		4.0f, distance, delta
+	);
+	CPPUNIT_ASSERT_EQUAL_MESSAGE(
+		"wrong surface normal at intersection point",
+		glm::vec3(0, 0, -1), normal
+	);
+
+	// turn ray around
+	ray.dir.z = -1;
+	CPPUNIT_ASSERT_MESSAGE(
+		"ray pointing away from box in front still intersects",
+		!Intersection(ray, box, M)
+	);
+
+	// move ray in front
+	ray.orig.z = 5;
+	CPPUNIT_ASSERT_MESSAGE(
+		"ray pointing at box behind does not intersect",
+		Intersection(ray, box, M, &distance, &normal)
+	);
+	CPPUNIT_ASSERT_DOUBLES_EQUAL_MESSAGE(
+		"intersection distance way off",
+		4.0f, distance, delta
+	);
+	CPPUNIT_ASSERT_EQUAL_MESSAGE(
+		"wrong surface normal at intersection point",
+		glm::vec3(0, 0, 1), normal
+	);
+
 	// 45 deg down from 4 units away, so should be about 4 * sqrt(2)
 	ray.orig = { -5.0f, 4.5f, 0.0f };
 	ray.dir = { 0.70710678118654752440f, -0.70710678118654752440f, 0.0f };
-- 
2.39.2