VR has taken many forms and formats since its inception, but this book will be focused on modern VR experienced with a Head-Mounted Display (HMD). HMDs such as the Oculus Rift are typically treated like an extra screen attached to your computer (more on that later), but with some extra components that enable it to capture its own orientation (and position, in some cases). This essentially amounts to a screen that sits on your head and knows how it moves, so it can mirror your head movements in the VR experience and enable you to look around the virtual world, making you feel like you're actually there:
Depth perception is another big principle of VR. Because the display of the HMD is always positioned right in front of the user's eyes, the rendered image is typically split into two images, one per eye, with each individual image rendered from the position of that eye.
You can observe the difference between normal rendering and VR rendering in the following two images. This first image is how normal 3D video games are rendered to a computer screen, created based on the position and direction of a virtual camera in the game world:
This next image shows how VR scenes are rendered, using a different virtual camera for each eye to create a stereoscopic depth effect:
