From 39985f36e807126b2c7b9ec6096bda3922903a54 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Sun, 15 Dec 2024 14:38:00 +0000
Subject: 2D triangle area support

---
 lib/triangle.h        |  7 +++++++
 test/test-geoData.cpp | 17 -----------------
 test/test-maths.cpp   | 34 ++++++++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 17 deletions(-)

diff --git a/lib/triangle.h b/lib/triangle.h
index 812bfab..5787094 100644
--- a/lib/triangle.h
+++ b/lib/triangle.h
@@ -31,6 +31,13 @@ struct Triangle : public glm::vec<3, glm::vec<Dim, T, Q>> {
 		return glm::length(crossProduct(sideDifference(1), sideDifference(2))) / T {2};
 	}
 
+	[[nodiscard]] constexpr auto
+	area() const
+		requires(Dim == 2)
+	{
+		return std::abs((sideDifference(1).x * sideDifference(2).y) - (sideDifference(2).x * sideDifference(1).y)) / 2;
+	}
+
 	[[nodiscard]] constexpr Normal3D
 	normal() const
 		requires(Dim == 3)
diff --git a/test/test-geoData.cpp b/test/test-geoData.cpp
index 5411b61..1ca050d 100644
--- a/test/test-geoData.cpp
+++ b/test/test-geoData.cpp
@@ -190,23 +190,6 @@ BOOST_DATA_TEST_CASE(walkTerrainUntil,
 	BOOST_CHECK_EQUAL_COLLECTIONS(visited.begin(), visited.end(), visits.begin(), visits.end());
 }
 
-BOOST_AUTO_TEST_CASE(triangle_helpers)
-{
-	constexpr static GeoData::Triangle<3> t {{0, 0, 0}, {5, 0, 0}, {5, 5, 0}};
-
-	BOOST_CHECK_EQUAL(t.nnormal(), up);
-	BOOST_CHECK_CLOSE(t.angle(0), quarter_pi, 0.01F);
-	BOOST_CHECK_CLOSE(t.angleAt({0, 0, 0}), quarter_pi, 0.01F);
-	BOOST_CHECK_CLOSE(t.angle(1), half_pi, 0.01F);
-	BOOST_CHECK_CLOSE(t.angleAt({5, 0, 0}), half_pi, 0.01F);
-	BOOST_CHECK_CLOSE(t.angle(2), quarter_pi, 0.01F);
-	BOOST_CHECK_CLOSE(t.angleAt({5, 5, 0}), quarter_pi, 0.01F);
-
-	BOOST_CHECK_CLOSE(t.angleAt({0, 1, 0}), 0.F, 0.01F);
-
-	BOOST_CHECK_CLOSE(t.area(), 12.5F, 0.01F);
-}
-
 using FindEntiesData = std::tuple<GlobalPosition2D, GlobalPosition2D, int>;
 
 BOOST_DATA_TEST_CASE(findEntries,
diff --git a/test/test-maths.cpp b/test/test-maths.cpp
index b9d08bb..1278c44 100644
--- a/test/test-maths.cpp
+++ b/test/test-maths.cpp
@@ -12,6 +12,7 @@
 #include <gfx/gl/camera.h>
 #include <glm/glm.hpp>
 #include <maths.h>
+#include <triangle.h>
 #include <tuple>
 
 using vecter_and_angle = std::tuple<glm::vec3, float>;
@@ -341,3 +342,36 @@ static_assert(linesIntersectAt(GlobalPosition2D {311000100, 491100100}, {3110500
 					  .value()
 		== GlobalPosition2D {311000100, 491100100});
 static_assert(!linesIntersectAt(glm::dvec2 {0, 1}, {0, 4}, {1, 8}, {1, 4}).has_value());
+
+BOOST_AUTO_TEST_CASE(triangle2d_helpers)
+{
+	constexpr static Triangle<2, float> t {{0, 0}, {5, 0}, {5, 5}};
+
+	BOOST_CHECK_CLOSE(t.angle(0), quarter_pi, 0.01F);
+	BOOST_CHECK_CLOSE(t.angleAt({0, 0}), quarter_pi, 0.01F);
+	BOOST_CHECK_CLOSE(t.angle(1), half_pi, 0.01F);
+	BOOST_CHECK_CLOSE(t.angleAt({5, 0}), half_pi, 0.01F);
+	BOOST_CHECK_CLOSE(t.angle(2), quarter_pi, 0.01F);
+	BOOST_CHECK_CLOSE(t.angleAt({5, 5}), quarter_pi, 0.01F);
+
+	BOOST_CHECK_CLOSE(t.angleAt({0, 1}), 0.F, 0.01F);
+
+	BOOST_CHECK_CLOSE(t.area(), 12.5F, 0.01F);
+}
+
+BOOST_AUTO_TEST_CASE(triangle3d_helpers)
+{
+	constexpr static Triangle<3, float> t {{0, 0, 0}, {5, 0, 0}, {5, 5, 0}};
+
+	BOOST_CHECK_EQUAL(t.nnormal(), up);
+	BOOST_CHECK_CLOSE(t.angle(0), quarter_pi, 0.01F);
+	BOOST_CHECK_CLOSE(t.angleAt({0, 0, 0}), quarter_pi, 0.01F);
+	BOOST_CHECK_CLOSE(t.angle(1), half_pi, 0.01F);
+	BOOST_CHECK_CLOSE(t.angleAt({5, 0, 0}), half_pi, 0.01F);
+	BOOST_CHECK_CLOSE(t.angle(2), quarter_pi, 0.01F);
+	BOOST_CHECK_CLOSE(t.angleAt({5, 5, 0}), quarter_pi, 0.01F);
+
+	BOOST_CHECK_CLOSE(t.angleAt({0, 1, 0}), 0.F, 0.01F);
+
+	BOOST_CHECK_CLOSE(t.area(), 12.5F, 0.01F);
+}
-- 
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