Presently, there are two basic categories of head-mounted displays for virtual reality—desktop VR and mobile VR.

It's probably worthwhile clarifying what virtual reality is not.

A sister technology to VR is augmented reality (AR), which superimposes computer generated imagery (CGI) over views of the real world. Limited uses of AR can be found on smart phones, tablets, handheld gaming systems such as the Nintendo 3DS, and even in some science museum exhibits, which overlay the CGI on top of live video from a camera.

The latest innovations in AR are the AR headsets, such as Microsoft HoloLens and Magic Leap, which show the computer graphics directly in your field of view; the graphics are not mixed into a video image. If the VR headsets are like closed goggles, the AR headsets are like translucent sunglasses that employ a technology called light fields to combine the real-world light rays with CGI. A challenge for AR is ensuring that the CGI is consistently aligned with and mapped onto the objects in the real-world space and eliminate latency while moving about so that they (the CGI and objects in real-world space) stay aligned.

AR holds as much promise as VR for future applications, but it's different. Though AR intends to engage the user within their current surroundings, virtual reality is fully immersive. In AR, you may open your hand and see a log cabin resting in your palm, but in VR, you're transported directly inside the log cabin and you can walk around inside it.

We can also expect to see hybrid devices that somehow either combine VR and AR, or let you switch between modes.

The consumer-level virtual reality starts with gaming. Video gamers are already accustomed to being engaged in highly interactive hyper-realistic 3D environments. VR just ups the ante.

Gamers are early adopters of high-end graphics technology. Mass production of gaming consoles and PC-based components in the tens of millions and competition between vendors leads to lower prices and higher performance. Game developers follow suit, often pushing the state-of-the-art, squeezing every ounce of performance out of hardware and software. Gamers are a very demanding bunch, and the market has consistently stepped up to keep them satisfied. It's no surprise that many, if not most, of the current wave of the VR hardware and software companies are first targeting the video gaming industry. A majority of the demos and downloads that are available on Oculus Share (https://share.oculus.com/) and Google Play for the Cardboard app (https://play.google.com/store/search?q=cardboard&c=apps) are games. Gamers are the most enthusiastic VR advocates and seriously appreciate its potential.

Game developers know that the core of a game is the game mechanics, or the rules, which are largely independent of the skin, or the thematic topic of the game. Gameplay mechanics can include puzzles, chance, strategy, timing, or muscle memory (twitch). VR games can have the same mechanic elements but might need to be adjusted for the virtual environment. For example, a first-person character walking in a console video game is probably going about 1.5 times faster than their actual pace in real life. If this wasn't the case, the player would feel that the game is too slow and boring. Put the same character in a VR scene and they will feel that it is too fast; it could likely make the player feel nauseous. In VR, you will want your characters to walk a normal, earthly pace. Not all video games will map well to VR; it may not be fun to be in the middle of a war zone when you're actually there.

That said, virtual reality is also being applied in areas other than gaming. Though games will remain important, non-gaming apps will eventually overshadow them. These applications may differ from games in a number of ways, with the most significant having much less emphasis on game mechanics and more emphasis on either the experience itself or application-specific goals. Of course, this doesn't preclude some game mechanics. For example, the application may be specifically designed to train the user at a specific skill. Sometimes, the gamification of a business or personal application makes it more fun and effective in driving the desired behavior through competition.

Here are a few examples of the kinds of non-gaming applications that people are working on:

Wow, that's quite a list! This is just the low-hanging fruit.

The purpose of this book is not to dive too deeply into any of these applications. Rather, I hope that this survey helps stimulate your thinking and provides a perspective towards how virtual reality has the potential to be virtually anything for everyone.

This book takes a practical, project-based approach to teach the specifics of virtual reality development using the Unity 3D game development engine. You'll learn how to use Unity 5 to develop VR applications, which can be experienced with devices such as the Oculus Rift or Google Cardboard.

However, we have a slight problem here—the technology is advancing very rapidly. Of course, this is a good problem to have. Actually, it's an awesome problem to have, unless you're a developer in the middle of a project or an author of a book on this technology! How does one write a book that does not have obsolete content the day it's published?

Throughout the book, I have tried to distill some universal principles that should outlive any near-term advances in virtual reality technology, that includes the following:

Once VR becomes mainstream, many of these lessons will perhaps be obvious rather than obsolete, just like the explanations from the 1980's on how to use a mouse would just be silly today.

There is not just one kind of virtual reality experience. In fact, there are many. Consider the following types of virtual reality experiences:

In this book, we will implement a number of projects that demonstrate how to build each of these types of VR experience. For brevity, we'll need to keep it pure and simple, with suggestions for areas for further investigation.

Each chapter of the book introduces new technical skills and concepts that are important if you wish to build your own virtual reality applications. You will learn about the following in this book:

We will write scripts in the C# language and use features of Unity as and when they are needed to get things done.

However, there are technical areas that we will not cover, such as realistic rendering, shaders, materials, and lighting. We will not go into modeling techniques, terrains, or humanoid animations. Effective use of advanced input devices and hand and body tracking is proving to be critical to VR, but we won't have a chance to get into it here either. We also won't discuss game mechanics, dynamics, and strategies. We will talk about rendering performance optimization, but not in depth. All of these are very important topics that may be necessary for you to learn (or for someone in your team), in addition to this book, to build complete, successful, and immersive VR applications.

In this chapter, we looked at virtual reality and realized that it can mean a lot of things to different people and can have different applications. There's no single definition, and it's a moving target. We are not alone, as everyone's still trying to figure it out. The fact is that virtual reality is a new medium that will take years, if not decades, to reach its potential.

VR is not just for games; it can be a game changer for many different applications. We identified over a dozen. There are different kinds of VR experiences, which we'll explore in the projects in this book.

VR headsets can be divided into those that require a separate processing unit (such as a desktop PC or a console) that runs with a powerful GPU and the ones that use your mobile phone for processing. In this book, we will use an Oculus Rift as an example of desktop VR and Google Cardboard as the example of mobile VR, although there are many alternative and new devices available.

We're all pioneers living at an exciting time. Because you're reading this book, you're one, too. Whatever happens next is literally up to you. As the personal computing pioneer Alan Kay said, "The best way to predict the future is to invent it."

So, let's get to it!

In the next chapter, we'll jump right into Unity and create our first 3D scene and learn about world coordinates and scaling. Then in Chapter 3, VR Build and Run, we'll build and run it on a VR headset, and we'll discuss how virtual reality really works.