From 4ef5c934aacbfce6b3c5502425975edcf61cf0e8 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Fri, 7 Jan 2022 18:57:08 +0000
Subject: Initial commit GeoData ray tracer

---
 game/geoData.cpp | 39 +++++++++++++++++++++++++++++++++++++++
 game/geoData.h   | 13 +++++++++++++
 2 files changed, 52 insertions(+)

(limited to 'game')

diff --git a/game/geoData.cpp b/game/geoData.cpp
index c3fb5dc..4537026 100644
--- a/game/geoData.cpp
+++ b/game/geoData.cpp
@@ -95,6 +95,45 @@ GeoData::positionAt(const glm::vec2 wcoord) const
 	return wcoord || heightMid;
 }
 
+GeoData::RayTracer::RayTracer(glm::vec2 p0, glm::vec2 p1, float scale) : p {glm::floor(p0)}, d {glm::abs(p1 - p0)}
+{
+	using Limits = std::numeric_limits<typename glm::vec2::value_type>;
+	static_assert(Limits::has_infinity);
+	static constexpr const glm::vec2 inf {Limits::infinity(), -Limits::infinity()};
+
+	auto byAxis = [this, p0, p1, scale](auto axis) {
+		if (d[axis] == 0) {
+			inc[axis] = 0;
+			return inf[axis];
+		}
+		else if (p1[axis] > p0[axis]) {
+			inc[axis] = scale;
+			return (std::floor(p0[axis]) + 1 - p0[axis]) * d[1 - axis];
+		}
+		else {
+			inc[axis] = -scale;
+			return (p0[axis] - std::floor(p0[axis])) * d[1 - axis];
+		}
+	};
+
+	error = byAxis(0);
+	error -= byAxis(1);
+	inc.z = scale;
+}
+
+glm::vec2
+GeoData::RayTracer::next()
+{
+	glm::vec2 cur {p};
+
+	static constexpr const glm::vec2 m {1, -1};
+	const int axis = (error > 0) ? 1 : 0;
+	p[axis] += inc[axis];
+	error += d[1 - axis] * m[axis] * inc.z;
+
+	return cur;
+}
+
 unsigned int
 GeoData::at(glm::ivec2 coord) const
 {
diff --git a/game/geoData.h b/game/geoData.h
index ffb7d64..7bd6ae5 100644
--- a/game/geoData.h
+++ b/game/geoData.h
@@ -32,6 +32,19 @@ public:
 	[[nodiscard]] float getScale() const;
 	[[nodiscard]] std::span<const Node> getNodes() const;
 
+	class RayTracer {
+	public:
+		RayTracer(glm::vec2 p0, glm::vec2 p1, float scale);
+
+		glm::vec2 next();
+
+	private:
+		glm::vec2 p;
+		const glm::vec2 d;
+		float error;
+		glm::vec3 inc;
+	};
+
 protected:
 	Limits limit {}; // Base grid limits first(x,y) -> second(x,y)
 	glm::uvec2 size {};
-- 
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