Trespass is a VR stealth experience developed with UnityVR and HTC VIVE. This experience invites the player to be a ninja and immerse in a VR vignette of 16th century Japan. Trespass takes cues from stealth genre classics Metal Gear Solid and Assassin's Creed. Players observe the movement of the non-player character of a samurai and use the environment to avoid being seen.
This project analyzed how people perceive virtual objects in VR. And it took advantage of people's perception to activate meaningful physical interactions. Meanwhile, it also involved a process of trial and error to determine what conventions of stealth games can be translated to VR and what we had to improve on.
Visual Design: worked as the art director on this team and responsible for the aesthetic and visual style of the game scene.
3D Modeling: built most of the 3D assets and assembled the palace scene in Unity 3D.
Level Design: co-worked with teammates to design the layout of the palace maze.
User Testing: conducted user testing sessions by observation, interviews, and surveys.
You can check out the video below to see my visual contributions to this game.
Use Perception in VR to Motivate Meaningful Physical Interactions
In virtual reality, we can see some virtual objects which don't actually exist in the physical space. The previous projects and research showed us people tend to perceive and respond to these virtual objects as they do in real life. For example, they would regard a virtual wall as a solid barrier they can't go through although they actually won't bump into anything.
By taking advantage of this aspect, we wanted to explore if we could use their perception to activate more meaningful physical interactions with the virtual objects. We were particularly interested in stealth behaviors to test if people can use these virtual objects to hide and cover themselves.
Genre Adaptation: Stealth Game into VR?
Stealth game is a traditional video game genre which involves lots of physical movements of the character in their game space. Since we were going to implement some physical interactions in our project as well, we wanted to figure out if we could adapt the conventions of stealth game into VR. So we structured the project as a game experience. Instead of using joystick or mouse to control, players were going to hide with their body movement.
What we explored was how to use narrative, scenic design, larger walking space, non-player villain and game mechanics to motivate players' stealth behaviors. In this way, we'll learn which physical behavior can be easily motivated, which can not.
Here's a video of our research. Or you can directly read the texts below.
Methods & Process
Storyboard & script
Before we started to design our projects, we decided to look at some classical stealth games to summarize the design conventions of stealth games. Here are three games we reviewed:
Main games of Assassin's Creed are set in an open world and presented from the third-person perspective where the protagonists take down targets using their combat and stealth skills with the exploitation of the environment. Freedom of exploration is given to the player the historical settings to finish main and side quests.
Metal Gear Solid
The player must navigate the protagonist, Solid Snake, through the game's areas without being detected by enemies. Detection is triggered by the player moving into an enemy's field of vision and sets off an alarm that draws armed enemies to his location.
To remain undetected, the player can perform techniques which make use of the environment, such as crawling under objects, using boxes as cover, ducking or hiding around walls, and making noise to distract enemies.
The player's task is to break into the neighbor's home and solve a series of puzzles in order to gather the items needed to unlock and access his basement. As the player explores the neighbor's house, they must not be spotted by the mysterious neighbor, or they will be chased down, and if the player is not quick enough to hide or escape, will be captured.
Here come the conventions that we summarized from stealth games. We wanted to test if these conventions can be translated into VR.
In order to incorporate the conventions above, a Japanese ninja genre is ideated to structure all of the stealth behaviors in this game. The player is a ninja who needs to infiltrate the palace of a despotic lord to get a sword back. But the palace is full of danger. The player needs to use his ninja tactics to hide in these rooms and avoid the eyesight of a terrifying samurai. We hoped to use this non-player guard to motivate players' spatial exploration.
The player starts the game in a small room where they are instructed to steal a golden sword from a despotic lord.
The player finds a secret passage in the wall. This leads them to the treasure room via an open-air balcony.
Opening the door, the player sees a samurai warrior who’s guarding the palace. The player needs to take advantage of the space to hide.
The player enters the treasure room and is treated to a sight of the golden sword. They must now bring it to his ninja master.
How the genre looks in the final prototype
Level Design & Impossible Space
In this game, we designed a maze-like palace to let the player explore. The player should figure out the routes of the samurai so he can avoid being caught.
In order to allow a wider range of walking exploration in this game, we implemented a concept called "impossible space" to allow us to maximize the size of the physical room in which the player move by shifting the virtual space around them. This shift is hidden from the player, which gives them an illusion of a large and consistent space.
We make the stealth room as large as the size of the physical room. And we put the sword into a treasure room beside it, which locates in an "impossible space" that people can't actually walk into. However, we set a trigger on the balcony of the palace. When people get out of the room, everything inside the room will be shifted. Without being noticed by the player, the treasure room in impossible space will be shifted into the position of the physical room. So, the player can enter the treasure room by just walking in a circle in the physical area.
In the meantime, we put a peephole in the stealth room. In this way, the player can realize there is another room beside. So, this can make them feel like they actually walk into the area beside their physical playing space.
This "impossible space" concept is a technique we borrowed from the previous project, Ares. But instead of developing a linear narrative experience which Ares did, we implemented it into a game exploration setting which gives much freedom to the players.
Level design in first user testing
We invited testers of different demographic background to try out our game. We used observations, surveys, and interviews to collect data from the testers. We also revised our games and level design based the feedbacks from the testings. The picture above shows the demo we used for our first user testing. The icons below shows the topic areas that we hope to test.
Will a terrifying non-human character encourage players' stealth behaviors?
We put a non-human samurai character in this game. He will patrol around the maze based on a preset route. We wanted to know if a threat could motivate players' stealth behaviors.
We designed a multi-room scene to give players much space to hide.
Players can make use of the doors and rooms to hide. We wanted to see if they would perceive the virtual barrier as a physical block to avoid the potential threat.
Will our version of "impossible space" work?
We put the trigger of space shift on the entrance to the balcony. When players are on the balcony, we shift the things inside of the room to make it become the treasure room. We wanted to test if people would notice the shift.
Here are the testing results. Basically, all of the above worked!
The samurai is a very effective way to enact the narrative in the game. And he pushed the players to find places to hide.
For the impossible space, people will not observe the shifting of the spaces. They will feel like there is a larger space for them to explore.
What's more, even if there is no physical existence of some barriers they see in the virtual world, they would still react to these visual illusions based on their knowledge in real life. For example, people will not try to walk across the wall in the virtual world. And they will not dare to go to the edge of the balcony because they feel that they would actually fall from the balcony if they walk too close to the edge.
A player was testing the game
The level redesign based on the feedback from user testings
However, we did find some new trouble we needed to fix from our user testings. We were going to redesign our level based these valuable feedbacks.
Easily get lost
1. Players might not be clear about what the task is.
2. The samurai is too frightening. Players can't keep calm to think.
3. Few people realize the sword is actually in the room next to them. They don't know where to go.
Sliding door issue
1. Players can't recognize sliding doors in VR.
2. It is hard for them to figure out how to open the slide door.
We solved the problems above with following modifications. We also added more stealth behaviors in this game to test.
Add narrative element: Ninja friend
In the new level, we decided to use narrative to help players have a clear thought of their goal. We added a ninja friend at the beginning of the game. He will instruct you how to play this game.
Make maze layout simpler
We moved out some furniture and made fewer rooms in our maze. We also paused the samurai for a while. In this way, we wanted to make players feel less stressed in order to allow them to think about stealth strategies.
Players can slide the door towards both sides
To solve the sliding door issues, we did researches on Japanese sliding doors. We found they can be sided towards both left and right. So, we changed our door to include this feature. On the other hand, we decreased the number of the doors in order to make them more readable.
Involve more types of stealth behaviors
In the first version, the stealth behaviors are as simple as hiding behind doors. So, in the new version, we wanted to involve more physical interactions. We put a screen and a vase in the stealth room to allow players take advantage of. We also changed the "impossible space" trigger into a secret hole. We hoped players would duck into the hole during the game. We took advantage of this by arranging the shifting environment to the immediate left and right of the hole while the space in front of them doesn't move.
A player was hiding behind a virtual vase
A player is ducking into a virtual hole
We conducted a second user testing for the new level design, which turned out our modifications basically solved most of the problems.
In conclusion, the narrative elements, non-player villain, intense scenic design and puzzles can all be successfully translated into VR as a motivation for stealth behaviors and spatial exploration.
As for the stealth behaviors, the immersion of virtual reality easily drove the players to physically interact with their environments. But it doesn't mean every stealth behavior can be directly copied into VR world.
For example, only a few people chose to actually hide behind a virtual vase since it was not a necessary action in this game. For other behaviors including jumping from the roof, crawling into a hole, people would hesitate to take these actions unless the narrative forces them to do. So, our note for designing a stealth game in VR is to add enough cues to guide players' actions.