Welcome, reader!
This is the first part of a series of articles, which delve into game design for VR platforms. We focus on the HTC Vive platform and room-scale VR. Many of the concepts also apply to other VR platforms and the critical analysis of different game design elements is transferable to other areas as well.

The articles are based on the Bachelor’s thesis of Jens-Stefan Mikson and the Tribocalypse VR game, which Jens-Stefan made during the thesis work. The analysis is based on the observations, critical thinking and trial-and-error while making Tribocalypse VR. We sincerely hope that the knowledge learned during the player testing and development of Tribocalypse VR is of help to everyone developing VR games!

In this article we will give an overview of different VR platforms and try to emphasize again what is it about VR that makes it so special. Next we describe the Tribocalypse VR (TVR) game with the game loop and mechanics, so that the reader can relate to in the next articles. Lastly we introduce concepts of immersion and clarity, which are essential tools in analyzing every element of a VR game.

Introduction to Virtual Reality

Virtual reality allows us to take virtual risks in order to gain virtual experience very similar to real life experience. Even though virtual reality itself is not a new concept, it is only now that the technology allows the VR developers to transform their imagination into immersive products that are available to a wide audience. The immersiveness is sometimes also called presence, which describes the extent to which the VR media can represent the real world. Since modern immersive VR is only now starting to become more widespread, the design patterns and user experience paradigms of VR are still unexplored. There is still very much to discover in terms of which design choices work in VR and which do not.

Our senses are what allow us to experience the reality around us. The experience of reality is based upon the sensory information we receive and then process in our brains.

Motion Sickness

It is important for a VR system to provide a seamless experience and provide appropriate responses in real time as the user explores their surroundings. Problems arise when there is a delay between the person’s actions and the system response which then disrupts the experience. The person becomes aware that they are in an artificial environment and thus the user is not immersed in the virtual world. For example, when the user tilts their head in real life but camera display in the VR does not change its orientation in response, the user will most likely experience motion sickness. This is due to the conflict between the vestibular system (balance system) in the user’s ears and their vision. The vestibular system sends a message to the user’s brain informing that the head is tilted, however the vision input says otherwise.

The Hardware

There are many different devices, which are used to achieve a VR experience. These include headsets, gloves, bodysuits, remote controllers etc.

The headset allows the user to look around the created virtual environments. These environments are mostly three dimensional and appear life-sized to the user. Some headsets are capable of tracking the user’s movement as well. This means if the user walks around in real life with the headset on, the user should also move in the VR environment accordingly.

The controllers can be used to track the user’s hand position, to allow the user to press buttons on the controllers for input and for sending haptic pulses (vibrations) to the user.
The peripherals that allow input from the user (gloves, remote controllers) can range from application to application. The analysis in this article series is based on headsets that allow the tracking of the user’s movement in 6 degrees of freedom; the input from the player is received through remote controllers.
Common hardware platforms for VR are HTC Vive, Oculus Rift, PlayStation VR, Google Daydream View and Samsung Gear VR. For additional comparison we recommend to check out this article.

Phone-Based Solutions

The Samsung Gear VR, Google Daydream and Google Cardboard require a phone to work. A phone is placed inside the headset, and the phone’s screen will act as a display for the user. Their downside is that they do not track the user’s translational movement but only the rotation. This means that even if the player moves around in real life, he stays put in the virtual reality world. This often causes motion sickness and thus, the user prefers to be stationary in real world.

Partial Tracking

PlayStation VR (PSVR) has the ability to track the player’s translational movement. The PSVR uses a camera, which is usually placed in front of the player, near the TV screen. This setup is similar to those used in Nintendo Wii’s controller tracking. The downside of this setup is that if the camera cannot “see” the headset or the remotes, the tracking is lost. This can occur when the player turns the headset away from the camera or if the front of the headset is covered with something. Due to this limitation, the experiences for those kinds of platforms should be designed in a way where the front of the headset will always be at least partially visible to the camera. This can be fixed by purchasing an additional camera or placing the camera in a very specific way.

Room-Scale Solutions

Oculus Rift and HTC Vive hardware allow for room-scale tracking, which means that these systems are able to track the player in a wider area and independent of the user’s real world rotation. This allows the player to crouch, crawl, jump and spin around without having tracking problems. Thus creating a more immersive experience. Oculus VR requires at least 2 sensors for 360-degree tracking but only 1 is included in the Oculus Rift’s set. Because of the out-of-the-box room-scale capabilities of HTC Vive, we chose that for developing the Tribocalypse VR game on.

Tribocalypse VR

Tribocalypse VR is a VR game, which was made by a team of students and game developers. The game was in development for 6 months, from the beginning of August 2016 to the beginning of February 2017 and is currently fully released on Steam digital distribution platform.

Here is the full development team of Tribocalypse VR:

• Jens-Stefan Mikson – Project Lead, Lead Programmer (University of Tartu)
• Raimond-Hendrik Tunnel – Programmer (University of Tartu)
• Marko Korbun – Marketing, Unity Developer
• Jaanus Jaggo – Visual Effects (University of Tartu)
• Erich Brutus – Lead Artist, 3D Artist (Tartu Art School)
• Reino Meensalu – 3D Artist (Tartu Art School)
• Egmond Merivee – 3D Artist (Tartu Art School)
• Leene Künnap – 2D Artist (Tartu Art College)
• Valeria Skabardis – 2D Artist (Tartu Art College)
• Sylvia Renate Prass – 2D Artist (Tartu Art College)
• Nathan Vaino – 2D Artist (Tartu Art School)
• Raido Kikas – Concept Artist (Tartu Art School)
• Ruudi Vinter – Quality Assurance (Estonian Information Technology College)
• Taavi Luik – Music & Audio Engineer

As lot of the game development areas were covered, there were many different VR-specific considerations from different perspectives.

The Game Loop

TVR is a wave-defender game where the player’s village is attacked by waves of enemies. The goal is to repel these enemies using various items and game mechanics. In the game the Vive controllers are represented by hand models.

The player can move around the levels by moving around in real life and teleporting to fixed positions in the levels. To teleport, the player casts a teleportation spell using the Vive controller’s touchpad. The hands are also used for picking up, holding and throwing items and pulling the bowstring of the bow.

When the game is launched the player is inside the Home Village level, which is essentially a cave. The player is first taught to cast fire and teleportation spells. This is done by showing a tutorial text on big stone slabs (see the image below). The player can move between different locations in the cave using the teleportation spell. Three of these locations allow the player to select a different level to play in. There the player can select a difficulty (easy, medium, hard). After the difficulty is selected, a new level is loaded.

In each of the three playable levels there is a menu to start a game. The player is placed on a platform, which sits high on a tree trunk. On the platform there is a bow and some bombs. The player can navigate the menu using the bow. After the game is started, a wave of enemies (fixed number) attack the village. The enemies have one of the two targets: the player or the totem pillar. The latter is present in each level. When enemies reach the totem pillar, they attack it. After a certain damage has been applied to the pillar, a piece will fall off. Some enemies will then try to deliver the piece away from the village. If all totem pieces are delivered away, the game is over for the player. If all enemies of the wave are killed before the pieces are delivered, the player wins the match and can continue playing the next wave. The next wave is harder than the previous one up to a cap of 30 levels.

See the video for the Valley level to get an overview of a level:

There are also 2 types of enemies who can attack the player by shooting arrows with a bow. If the player gets hit by the arrow then the currently held items will be dropped, the display will be rendered in grayscale and the player is unable to pick up any new items. This state will last for 5 seconds.

To defeat the enemies, the player can use 3 offensive weapons: the bow, spears and bombs. The bow requires two hands to use and spears and bombs require one. Spears and bombs are throwable weapons. The player can also use a defensive shield to block any incoming arrows fired by the enemies.

For each kill the player receives score. This score can be used to purchase additional bomb slots in between the waves. Highest scores of each player will be saved and displayed in Steam’s global leader board. The player can receive extra score for performing certain actions such as killing multiple opponents in a short amount of time or receiving more score the further the opponents are from the player at the time of killing etc.

In order to better understand the game loop and mechanics, we recommend to go and try out the game yourself. Subsequently here there will be an analysis describing the design choices and different considerations encountered in Tribocalypse VR development.

Here is also a video demonstrating the gameplay from BrometheusTV:

Immersion & Clarity

Spatial presence and flow are considered by Weibel and Wissmath in their article “Immersion in Computer Games: The Role of Spatial Presence and Flow” (2011) to be the key concepts for explaining immersive experiences. Spatial presence refers to the sensation of being there in a mediated world, whereas flow rather refers to the sensation of being involved in the gaming action. They also state that the clarity of player’s actions has a big role when trying to increase the flow of a game. This is the reason why here clarity, alongside with spatial presence, is used as a part of a measurement tool for assessing the quality of certain game aspects of TVR. A feature that has a good level of clarity means that it feels natural for the player and causes no confusion. Even though the article by Weibel and Wissmath considers immersion to be a combination of spatial presence and flow, this work hereinafter uses the term immersion to refer to spatial presence alone. This is due to the fact that when players usually describe the games they play as immersive, they mean in fact the spatial presence.

We propose a measurement tool of immersion and clarity. That tool is used to analyse each design decision, problem and solution in this article series. For each game element it is described how immersive and clear an element of a game is. Every statement about immersiveness or clarity is objectively and logically explained. Usually when an element of a game has little clarity, the players will feel confused. Likewise, if the player is not immersed the game the game will mostly likely be boring for the player. The measurement of immersion and clarity can be used for many aspects of a computer game. Levels of a game can be described as immersive if they feel consistent. Level’s clarity can be measured based on how well the level guides the player towards his goal. Graphical user interface can be immersive if it fits well into the game world; it should also be easy to use (clarity). Level design, graphical user interface and game mechanics will be analysed in the subsequent parts of this article series based on their level of immersion and clarity. The analysis will focus on VR, which means that the solutions proposed in the subsequent articles in this series might not work when designing non-VR games.

Read the part 2 on the environment and level design considerations for TVR.