From a2e0c07c6a63539776b108f8ac88cd4781449aab Mon Sep 17 00:00:00 2001
From: Cyberarm <matthewlikesrobots@gmail.com>
Date: Wed, 7 Aug 2019 23:03:40 -0500
Subject: [PATCH] Added Ray class

---
 lib/cyberarm_engine.rb         |  1 +
 lib/cyberarm_engine/lib/ray.rb | 55 ++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)
 create mode 100644 lib/cyberarm_engine/lib/ray.rb

diff --git a/lib/cyberarm_engine.rb b/lib/cyberarm_engine.rb
index 89ba8c2..70cad80 100644
--- a/lib/cyberarm_engine.rb
+++ b/lib/cyberarm_engine.rb
@@ -9,6 +9,7 @@ require_relative "cyberarm_engine/engine"
 
 require_relative "cyberarm_engine/lib/bounding_box"
 require_relative "cyberarm_engine/lib/vector"
+require_relative "cyberarm_engine/lib/ray"
 require_relative "cyberarm_engine/lib/shader" if defined?(OpenGL)
 require_relative "cyberarm_engine/background"
 
diff --git a/lib/cyberarm_engine/lib/ray.rb b/lib/cyberarm_engine/lib/ray.rb
new file mode 100644
index 0000000..6806c4b
--- /dev/null
+++ b/lib/cyberarm_engine/lib/ray.rb
@@ -0,0 +1,55 @@
+module CyberarmEngine
+  class Ray
+    def initialize(origin, direction)
+      raise "Origin must be a Vector!" unless origin.is_a?(Vector)
+      raise "Direction must be a Vector!" unless direction.is_a?(Vector)
+
+      @origin  = origin
+      @direction = direction
+
+      @inverse_direction = @direction.inverse
+    end
+
+    def intersect?(intersectable)
+      if intersectable.is_a?(BoundingBox)
+        intersect_bounding_box?(intersectable)
+      else
+        raise NotImplementedError, "Ray intersection test for #{intersectable.class} not implemented."
+      end
+    end
+
+    # Based on: https://tavianator.com/fast-branchless-raybounding-box-intersections/
+    def intersect_bounding_box?(box)
+      tmin = -Float::INFINITY
+      tmax = Float::INFINITY
+
+      tx1 = (box.min.x - @origin.x) * @inverse_direction.x
+      tx2 = (box.max.x - @origin.x) * @inverse_direction.x
+
+      tmin = max(tmin, min(tx1, tx2))
+      tmax = min(tmax, max(tx1, tx2))
+
+      ty1 = (box.min.y - @origin.y) * @inverse_direction.y
+      ty2 = (box.max.y - @origin.y) * @inverse_direction.y
+
+      tmin = max(tmin, min(ty1, ty2))
+      tmax = min(tmax, max(ty1, ty2))
+
+      tz1 = (box.min.z - @origin.z) * @inverse_direction.z
+      tz2 = (box.max.z - @origin.z) * @inverse_direction.z
+
+      tmin = max(tmin, min(tz1, tz2))
+      tmax = min(tmax, max(tz1, tz2))
+
+      return tmax >= max(tmin, 0.0);
+    end
+
+    def min(x, y)
+      ((x) < (y) ? (x) : (y))
+    end
+
+    def max(x, y)
+      ((x) > (y) ? (x) : (y))
+    end
+  end
+end
\ No newline at end of file