From 3931bda936aba6ddae26c1d9f1d450781df800e8 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Fri, 3 Nov 2023 20:12:03 +0000
Subject: Implement terrain intersect ray

---
 game/terrain2.cpp     | 23 +++++++++++++++++++++++
 game/terrain2.h       |  4 ++++
 test/test-terrain.cpp | 12 ++++++++++++
 3 files changed, 39 insertions(+)

diff --git a/game/terrain2.cpp b/game/terrain2.cpp
index b129284..d1af221 100644
--- a/game/terrain2.cpp
+++ b/game/terrain2.cpp
@@ -135,6 +135,29 @@ TerrainMesh::positionAt(const PointFace & p) const
 	return p.point ^ out[0];
 }
 
+[[nodiscard]] std::optional<glm::vec3>
+TerrainMesh::intersectRay(const Ray & ray) const
+{
+	return intersectRay(ray, findPoint(ray.start));
+}
+
+[[nodiscard]] std::optional<glm::vec3>
+TerrainMesh::intersectRay(const Ray & ray, FaceHandle face) const
+{
+	std::optional<glm::vec3> out;
+	walkUntil(PointFace {ray.start, face}, ray.start + (ray.direction * 10000.F), [&out, &ray, this](FaceHandle face) {
+		glm::vec2 bari {};
+		float dist {};
+		Triangle<3> t {this, fv_range(face)};
+		if (glm::intersectRayTriangle(ray.start, ray.direction, t[0], t[1], t[2], bari, dist)) {
+			out = t * bari;
+			return true;
+		}
+		return false;
+	});
+	return out;
+}
+
 void
 TerrainMesh::walk(const PointFace & from, const glm::vec2 to, const std::function<void(FaceHandle)> & op) const
 {
diff --git a/game/terrain2.h b/game/terrain2.h
index da9f823..5539a50 100644
--- a/game/terrain2.h
+++ b/game/terrain2.h
@@ -1,9 +1,11 @@
 #pragma once
 
 #include "collections.h" // IWYU pragma: keep IterableCollection
+#include "ray.h"
 #include <OpenMesh/Core/Mesh/TriMesh_ArrayKernelT.hh>
 #include <filesystem>
 #include <glm/vec2.hpp>
+#include <optional>
 #include <thirdparty/openmesh/glmcompat.h>
 
 struct TerrainTraits : public OpenMesh::DefaultTraits {
@@ -66,6 +68,8 @@ public:
 	[[nodiscard]] FaceHandle findPoint(glm::vec2, FaceHandle start) const;
 
 	[[nodiscard]] glm::vec3 positionAt(const PointFace &) const;
+	[[nodiscard]] std::optional<glm::vec3> intersectRay(const Ray &) const;
+	[[nodiscard]] std::optional<glm::vec3> intersectRay(const Ray &, FaceHandle start) const;
 
 	void walk(const PointFace & from, const glm::vec2 to, const std::function<void(FaceHandle)> & op) const;
 	void walkUntil(const PointFace & from, const glm::vec2 to, const std::function<bool(FaceHandle)> & op) const;
diff --git a/test/test-terrain.cpp b/test/test-terrain.cpp
index 38cb51f..53eebfb 100644
--- a/test/test-terrain.cpp
+++ b/test/test-terrain.cpp
@@ -104,6 +104,18 @@ BOOST_DATA_TEST_CASE(findPositionAt,
 	BOOST_CHECK_CLOSE_VEC(fixedTerrtain.positionAt(p), p ^ h);
 }
 
+using FindRayIntersectData = std::tuple<glm::vec3, glm::vec3, glm::vec3>;
+
+BOOST_DATA_TEST_CASE(findRayIntersect,
+		boost::unit_test::data::make<FindRayIntersectData>({
+				{{310000, 490000, 50}, {1, 1, -2}, {310008.59, 490008.59, 32.834301}},
+				{{310000, 490000, 50}, {1, 1, -1}, {310017.12, 490017.12, 32.868526}},
+		}),
+		p, d, i)
+{
+	BOOST_CHECK_CLOSE_VEC(fixedTerrtain.intersectRay({p, d}).value(), i);
+}
+
 using WalkTerrainData = std::tuple<glm::vec2, glm::vec2, std::vector<int>>;
 
 BOOST_DATA_TEST_CASE(walkTerrain,
-- 
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