Implement Geometric Class Definitions (round 2)

include/J3ML/Geometry/Frustum.h

@@ -7,6 +7,23 @@
 
 namespace Geometry
 {
+
+    enum class FrustumType
+    {
+        Invalid,
+        /// Set the Frustum type to this value to define the orthographic projection formula. In orthographic projection,
+        /// 3D images are projected onto a 2D plane essentially by flattening the object along one direction (the plane normal).
+        /// The size of the projected images appear the same independent of their distance to the camera, and distant objects will
+        /// not appear smaller. The shape of the Frustum is identical to an oriented bounding box (OBB).
+        Orthographic,
+        /// Set the Frustum type to this value to use the perspective projection formula. With perspective projection, the 2D
+        /// image is formed by projecting 3D points towards a single point (the eye point/tip) of the Frustum, and computing the
+        /// point of intersection of the line of the projection and the near plane of the Frustum.
+        /// This corresponds to the optics in the real-world, and objects become smaller as they move to the distance.
+        /// The shape of the Frustum is a rectangular pyramid capped from the tip.
+        Perspective
+    };
+
     class Frustum {
     public:
         Plane TopFace;