From a0f1dc90aabd4cb5cfe2aef7116af170e6d0b953 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Tue, 31 Oct 2023 01:26:58 +0000
Subject: Helper type for storing/passing/returning a point and its containing
 face

point is const as face is mutable as a cache of the face containing
point.
---
 game/terrain2.cpp     | 18 ++++++++++++++++++
 game/terrain2.h       | 10 ++++++++++
 test/test-terrain.cpp |  9 +++++++++
 3 files changed, 37 insertions(+)

diff --git a/game/terrain2.cpp b/game/terrain2.cpp
index 3e24778..e98cebb 100644
--- a/game/terrain2.cpp
+++ b/game/terrain2.cpp
@@ -54,6 +54,24 @@ TerrainMesh::findPoint(glm::vec2 p) const
 	return findPoint(p, *faces_begin());
 }
 
+bool
+TerrainMesh::locate(const TerrainMesh::PointFace & pointFace, FaceHandle start) const
+{
+	if (pointFace.face.is_valid()) {
+		assert(triangleContainsPoint(pointFace.point, pointFace.face));
+		return true;
+	}
+	else {
+		return (pointFace.face = findPoint(pointFace.point, start)).is_valid();
+	}
+}
+
+bool
+TerrainMesh::locate(const TerrainMesh::PointFace & pointFace) const
+{
+	return locate(pointFace, *faces_begin());
+}
+
 namespace {
 	[[nodiscard]] constexpr inline bool
 	pointLeftOfLine(const glm::vec2 p, const glm::vec2 e1, const glm::vec2 e2)
diff --git a/game/terrain2.h b/game/terrain2.h
index 848c36e..e516719 100644
--- a/game/terrain2.h
+++ b/game/terrain2.h
@@ -18,6 +18,13 @@ class TerrainMesh : public OpenMesh::TriMesh_ArrayKernelT<TerrainTraits> {
 public:
 	explicit TerrainMesh(const std::filesystem::path &);
 
+	struct PointFace {
+		PointFace(const glm::vec2 p) : point {p} { }
+
+		const glm::vec2 point;
+		mutable FaceHandle face {};
+	};
+
 	[[nodiscard]] FaceHandle findPoint(glm::vec2) const;
 	[[nodiscard]] FaceHandle findPoint(glm::vec2, FaceHandle start) const;
 
@@ -28,4 +35,7 @@ protected:
 	[[nodiscard]] static bool triangleContainsPoint(const glm::vec2, const glm::vec2, const glm::vec2, const glm::vec2);
 	[[nodiscard]] bool triangleContainsPoint(const glm::vec2, FaceHandle) const;
 	[[nodiscard]] bool triangleContainsPoint(const glm::vec2, ConstFaceVertexIter) const;
+
+	bool locate(const PointFace &) const;
+	bool locate(const PointFace &, FaceHandle start) const;
 };
diff --git a/test/test-terrain.cpp b/test/test-terrain.cpp
index 429207c..f737f4f 100644
--- a/test/test-terrain.cpp
+++ b/test/test-terrain.cpp
@@ -46,6 +46,15 @@ BOOST_AUTO_TEST_CASE(trianglesContainsPoints)
 	}
 }
 
+BOOST_AUTO_TEST_CASE(locatePointFace)
+{
+	const PointFace pf {{310002, 490003}};
+	BOOST_CHECK(!pf.face.is_valid());
+	BOOST_CHECK(locate(pf));
+	BOOST_CHECK(pf.face.is_valid());
+	BOOST_CHECK_EQUAL(pf.face.idx(), 0);
+}
+
 BOOST_AUTO_TEST_SUITE_END();
 
 using FindPointData = std::tuple<glm::vec2, int>;
-- 
cgit v1.2.3