Interaction system

As previously mentioned, the interaction system was designed to work with the Vive^TM Controllers.

The button layout on the controllers includes.

• a trigger button, corresponding to the index finger;

• a directional pad on the top, which can be used as touch-pad or as button with the thumb;

• two grip buttons on both sides, which can be pressed with middle and ring fingers.

In the direction of reducing the confusion for inexperienced user, the known set of colors Cyan, Magenta, Yellow was used to respectively indicate Grips, Trigger and Pad. Along with the color, every button also have a specific function.

• the trigger button can be used to interact with objects (open/close, lift/drop, switch on/off);

• the pad can be used to show/hide the official brochure and to use the extin-guisher (if already unlocked with the other hand);

• grips, useful with the Arm-Swing locomotion mode only, enable the movement inside the virtual environment.

The interaction is performed through a small spherical Trigger¹⁷ placed on top of each hand. Every interactive object, to work with the system, requires:

• a Collider component;

• a Rigid Body component;

• a Generic Item component.

Generic Item contains various data related with the object, including various flags indicating if it ca be grabbed or not, if it is enabled or not and if the interaction with the item is enabled or disabled. In addition, the above-mentioned class can be ex-panded by exploiting the inheritance¹⁸ technique in order to add useful information for specific objects while keeping the backward compatibility with the interaction system.

For objects which can be grabbed, an additional logic have been used; at the begin-ning of the simulation, the Item Controller object will instantiate an hidden copy of every object which could be eventually grabbed as children of every hand. The objects spawned with this logic are attached with a script named Grabbed Item, which can be extended to support the behavior of the different usable objects.

When the player will try to grab an object, the script will:

1. parent the original object to the hand, enabling inside the Rigid Body¹⁹ com-ponent the IsKinematic²⁰ flag;

2. hide the original object;

3. show the corresponding grabbed object;

4. copy the state of the generic item to the grabbed object (for example, consid-ering the extinguisher, the fuel amount would be assigned).

17A Collider component set as trigger will not be involved in the physic collision management, but will send collision messages to the attached script when a Rigid Body interacts with it

18Programming technique with which new classes can be created by reusing, extending, and modifying the behavior that is defined in other classes

19Unity component used to enable physics on a GameObject

20Flag used to make a Rigid Body unaffected by external forces

When the player will later drop the object, the script will:

1. copy the state of the grabbed item to the hidden original object;

2. hide the grabbed object;

3. show again the hidden original object;

4. remove the parenting with the hand;

5. set the IsKinematic flag to false.

Following this logic, the grabbed object can be placed in advance in the proper position in respect of the hand, and the object components can be separated between the Generic Item and the Grabbed Item (e.g. in case of the extinguisher, only the grabbed version will have the particle system and the relative script attached).

The complete list of the implemented interactions is reported in Tables 5.5 and 5.6.

Table 5.5: Interactions inside vehicle Interaction Item Description

Hazard lights button

The hazards lights button will enable the relative car function, signaling the danger to other drivers.

Not enabling it will be counted as error

Car key The car key let you to turn off the vehicle. Leaving it enabled will result in an error

Car handle

The car handle will let the user go outside of the vehicle, continuing with the simulation. Staying in the vehicle will temporarily protect him or her from the smoke, but the car could eventually catch fire due to radiation

Table 5.6: Interaction inside the tunnel Interaction Item Description

SOS button The fire alarm, placed on the SOS column, will send an alarm to the tunnel headquarter

Niche door Opening the niche door will grant the user access to the SOS telephone and to the extinguisher

SOS telephone With the SOS telephone the user can ask for the help of an operator along with triggering an alarm

Extinguisher

The extinguisher can extinguish the fire, but has a limited amount of fuel and it must be unlocked before usage

Shelter door

When the user enters the shelter, the game will give him or her few seconds to use the SOS telephone, then will end the simulation

Car handle Using the external car handle, the user can go back into the car

An additional interaction method was developed to manage the UI inside the Main Menu; for that scene, a ray-cast²¹ logic with a visual ray coming out from the right controller is used to interact with the environment along with the classic method.

A similar system was also implemented inside the First Person Controller, in order to allow the previously mentioned interactions with mouse and keyboard too. To facilitate the usage of the system, a cross-hair was applied on the screen, whose color is used to signal the availability of any interaction.

Figure 5.13: Ray-cast interaction logic at work with the First Person Controller

21Given a point and a direction, a ray is projected in order to find intersections with other objects