What is Frustum ?
Mathematically frustum is a solid portion of a Cone or Pyramid, The frustum is usually used in game engine to speak about the camera frustum. Camera frustum represents the zone of vision of a camera. Without limit, we have a pyramid but with near and far we have a frustum.
Frustum Culling means drawing only geometries or triangles that is present inside the camera frustum and discarding what’s outside the camera frustum.
How to mathematically represent a frustum? Thanks to 6 planes: near, far, right, left top and bottom planes. So, an object is visible if it is forward or on the 6 planes. Mathematically a plane is represented with a normal vector and distance to the origin. A plane doesn’t have any size or limit as a quad.