From 94f0e426bc8f298aec90fd0d4fcf6f823f8c399c Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Mon, 10 Jan 2022 02:07:53 +0000
Subject: Ray Trace cursor clicks to terrain surface

---
 game/geoData.cpp | 34 ++++++++++++++++++++++++++++++++++
 game/geoData.h   |  4 ++++
 2 files changed, 38 insertions(+)

(limited to 'game')

diff --git a/game/geoData.cpp b/game/geoData.cpp
index 32ec55e..c9e909b 100644
--- a/game/geoData.cpp
+++ b/game/geoData.cpp
@@ -4,8 +4,10 @@
 #include <array>
 #include <cmath>
 #include <cstddef>
+#include <glm/gtx/intersect.hpp>
 #include <maths.h>
 #include <random>
+#include <ray.hpp>
 #include <stb/stb_image.h>
 #include <stdexcept>
 #include <util.h>
@@ -132,6 +134,38 @@ GeoData::RayTracer::next()
 	return cur;
 }
 
+std::optional<glm::vec3>
+GeoData::intersectRay(const Ray & ray) const
+{
+	if (glm::length(!ray.direction) <= 0) {
+		return {};
+	}
+	RayTracer rt {ray.start / scale, ray.direction};
+	while (true) {
+		const auto n {rt.next() * scale};
+		try {
+			const auto point = quad(n);
+			for (auto offset : {0U, 1U}) {
+				glm::vec2 bary;
+				float distance;
+				if (glm::intersectRayTriangle(ray.start, ray.direction, point[offset], point[offset + 1],
+							point[offset + 2], bary, distance)) {
+					return point[offset] + ((point[offset + 1] - point[offset]) * bary[0])
+							+ ((point[offset + 2] - point[offset]) * bary[1]);
+				}
+			}
+		}
+		catch (std::range_error &) {
+			const auto rel = n / !ray.direction;
+			if (rel.x > 0 && rel.y > 0) {
+				return {};
+			}
+		}
+	}
+
+	return {};
+}
+
 unsigned int
 GeoData::at(glm::ivec2 coord) const
 {
diff --git a/game/geoData.h b/game/geoData.h
index a296205..42c2d9d 100644
--- a/game/geoData.h
+++ b/game/geoData.h
@@ -2,10 +2,13 @@
 
 #include <filesystem>
 #include <glm/glm.hpp>
+#include <optional>
 #include <span>
 #include <utility>
 #include <vector>
 
+class Ray;
+
 class GeoData {
 public:
 	struct Node {
@@ -22,6 +25,7 @@ public:
 	void loadFromImages(const std::filesystem::path &, float scale);
 
 	[[nodiscard]] glm::vec3 positionAt(glm::vec2) const;
+	[[nodiscard]] std::optional<glm::vec3> intersectRay(const Ray &) const;
 
 	[[nodiscard]] unsigned int at(glm::ivec2) const;
 	[[nodiscard]] unsigned int at(int x, int y) const;
-- 
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