GaDeVi

Game Development Integrating Tracking and Visualization Devices into Virtools

Ricardo Aguiar

, João Madeiras Pereira

IST/UTL, Lisbon, Portugal

IST/UTL INESC-ID, Lisbon, Portugal

José Braz

EST/IPS, Setúbal, Portugal

Keywords: Virtual Reality, Immersive Devices, Game Engine, Computer Game, Interactivity, Immersion.

Abstract: Computer and console games are increasingly using non-computer conventional input/output devices. This

work’s main goal was to create an interactive 3D application with Virtools, a development tool that appeals

to the player dexterity and astuteness through the use of several immersive, non-computer conventional

devices like magnetic trackers, data gloves and VR glasses. The present paper describes the integration of

interaction and visualization devices into Virtools as well as the development of two games using the VR

environment. To finalize the assessment of the performance measurements and user tests is given.

1 INTRODUCTION

Nowadays, computer and console games are an

increasingly profitable market (ELSPA, 2003). In

fact, one of the main driving factors for hardware

and technological evolution in IT occur because of

the increasing need of greater capacity for

processing data to simulate high complexity physical

effects and/or offer a realistic visual quality in a

game. Videogame programming is also a very

interesting area of development. Trying to give the

gamer a complete immersive experience becomes a

challenge (Goebel et al, 2001). However most of

today’s games are limited to standard input/output

devices, like a mouse and a keyboard on a PC or a

game pad on a game console. This last statement

was true in 2004 (Hinckley et al, 2004) and still true

today, even if it should be mentioned that the Wii

platform is the exception in the console market.

Moreover the game 3D content is almost always

displayed into a 2D screen such as CRT or LCD.

The goal for this work is to create games with

professional developing tools that offer new ways of

interaction with the player through the use of

immersive devices. The visualization will not be

made by a normal 2D screen but through a set of VR

Glasses in order to give a more realistic awareness

of all three dimensions.

Virtools 4.0 was the main platform to develop

the games along with Visual Studio.Net (Microsoft)

which was used to create new features/plug-ins. The

following immersive devices where programmed

into the games: Magnetic tracker Fastrak

(Polhemus), Data Gloves Ultra (5DT) and Z800 3D

Visors (eMagin). Blender and 3D Studio Max

(Autodesk) were used as modelling and skinning

tools.

2 TECHNOLOGY DESCRIPTION

This section introduces all three devices listed above

and provides a brief description of Virtools.

2.1 Polhemus Fastrak

A tracker’s purpose is to provide real time

information of the location and movement of a

receiver module relatively to an emitter module.

Relative spatial coordinates (x, y, z) and three Euler

313

Aguiar R., Madeiras Pereira J. and Braz J. (2009).

GaDeVi - Game Development Integrating Tracking and Visualization Devices into Virtools .

In Proceedings of the Fourth International Conference on Computer Graphics Theory and Applications, pages 313-321

DOI: 10.5220/0001755003130321

 SciTePress

angles (azimuth, elevation, roll), thus six degrees of

freedom, are given to the user. A tracker device has

three main components (Polhemus, 2005), an

interface module, also called filter, an emitter

module and finally a receiver module.

(a)

(b)

Figure 1: 5DT Data Gloves. (a) 5 Sensor Model, (b) 14

Sensor Model.

Figure 2: Behavioural Building Block Layout.

2.2 5DT Data Gloves

Data gloves capture hands motion. Several sensors

are placed into specific positions of the glove in

order to capture finger motion, process this data and

supply it to the computer. The models which are

used in this work are Left Handed 5 5DT Data Glove

Ultra and Right Handed 14 5DT Data Glove 14

Ultra (5DT, 2004). These models main differences

are in the number of sensors available at the glove.

2.3 eMagin Z800 3D Visor

A pair of VR Glasses is used instead of a 2d screen

enhancing depth perception which is achieved using

stereoscopy.

Stereoscopy is defined as the creation of a three-

dimensional image by presenting two slightly

different images to each of the human eye. Several

algorithms exist that perform stereoscopy. The most

popular techniques are anaglyph, passive stereo and

active stereo. With anaglyph, an image is

constructed with two overlapped layers, each one

filtered with a different colour. The viewer must

wear a special set of glasses in which each lens has a

different colour.

Passive stereo principle uses light polarization to

transmit a rendered stereo pair. The image is

recombined into the glasses lens through filters.

Active stereo, implemented in 3D Visors, transmits

two different images, with the Graphics Card

Vertical Sync controlling its frequency. Each one of

those images is sent to micro displays located in

left/right eye.

3D Visor also provides tracking information

using accelerometers and an internal gyroscope,

making possible to know the headset orientation and

type of movement.

2.4 Dassault Systèmes Virtools

Virtools, a game engine, was the main platform used

in this game development. It has the advantage of

creating interactive 3D content for computers and

consoles in a fast and intuitive way using Product

Context Scenario “PCS” (Mc Carthy et al, 2006), a

Virtools proprietary programming paradigm. PCS

allows a programmer to create applications using

only drag & drop operations of special entities called

behavioral Building Blocks (BB). A BB has the

aspect shown in Figure 2.

It has five main components:

• Behavioural Inputs (bIn)

• Behavioural Outputs (bOut)

• Parameter Inputs (pIn)

• Parameter Outputs (pOut)

• Properties marks.

The bIn is where the BB receives an activating

signal to start its internal processing; bOut generates

an activation signal when the BB has finished which

is then propagated to other BB. Through pIn and

pOut, data is transmitted between BB, receiving

external data in pIn and transmitting data through

pOut. The “Properties mark” indicates if:

• BB may send/receive messages through

scripts

• Parameters processing may be changed

• New bIn, bOut, pIn, pOut may be inserted

into the BB.

The Virtools layout has three main components,

3D Layout, Building Blocks & Data Resources, and

Manager & Schematic Window, as shown on Figure

In 3D Layout, common abstract objects in a

typical game engine like cameras or lights, may be

created and placed in a game. 2D and 3D content of

a Level may be manipulated in directly at the 3D

Layout, using transformation operations. It is also

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possible to change camera parameters like field of

view, panning, etc.

Inside Building Blocks & Data Resources, all

available behavioural Building Blocks are listed and

are ready to use, as well as a set of native Virtools

resources like images, sounds and so on as shown on

Figure 4.

Figure 3: Virtools Main Layout.

Finally in Level Manager & Schematic Window,

all the Level objects are listed in the Level Manager

section, allowing the programmer to access their

setup. It is also possible to create new scripts and

logical entities like Arrays, Groups, etc. In the

Schematic Window scripts are programmed by

filling them with BBs, Parameter Operations and

Variables as shown in Figure 5.

3 DEVICES INTEGRATION

Virtools standard version does not support the set of

immersive devices listed above, so it is necessary to

integrate them. This process is made using the

Virtools SDK and the devices specific Application

Programming Interfaces. New BB and Managers are

created with SDK using C++. To develop a new BB

it is necessary to establish the number of bIn/ bOut,

the number and type of pIn/pOut, types of properties

marks and define an execution function which has

the desired BB internal processing and bOut

activation. A Manager, manages data resources,

external communications, etc. The order through

which the managing process is performed must be

defined in a Manager. It may be done after or before

a frame is processed.

3.1 Polhemus Fastrak Integration

Polhemus Fastrak API programming interface,

FTAPI, allows the connection and communication

between the PC and tracker. After an established

connection, the programmer may request data such

as relative position in rectangular coordinates [x, y,

z] and orientation in Euler angles [Azimuth,

Elevation, Roll] of one of four possibly connected

receivers to a unique transmitter.

A single behavioural Building Block is

developed with FTAPI, which is responsible by

managing the trackers communication with the PC

and supply its data to the programmer. However,

this approach decreases drastically the applications

overall performance with frame rates falling down

from 60 to 5-10 fps. To overcome this lack of

performance, a Manager is created and made

responsible for the communication with the tracker

and supplying the requested data to a newly

developed BB, named TrackerBB The programmer

may change from which receiver he wants to obtain

tracking data inserting a valid receiver id into

StationId pIn as shown in Figure 6.

The Manager, before each frame is processed,

requests new data from the specified receiver and

make it available to TrackerBB to use it in a

composition. The tracking data from the BB may be

used through its pOuts which specify, from left to

right:

Vector with relative rectangular receiver

coordinates [x y, z]

• Receiver’s relative Azimuth angle

orientation

• Receiver’s relative Elevation angle

orientation

• Receiver’s relative Roll angle orientation

• Connection Status

• Tracker Debug Information

• Tracker internal latency time, first 32 bits

• Tracker internal latency time, last 32 bits

Using the BB - Manager Scheme increases the

frame rate up to 30 fps.

3.2 5DT Integration

A similar plug-in is developed for the data gloves. A

Manager is created with Virtools SDK and FGlove

API. As in the tracker, it manages the

communication and data flow from the gloves and a

newly developed BB named GloveBlock.

GloveBlock has two pIn: Mode and gloveId.

Mode indicates if the sensors outputs are raw or

auto-calibrated values. If raw data is selected the

values are given in a range of 0-4095 (12 bit

resolution) in which 0 is no sensor flexure and 4095

is total sensor flexure. In case calibrated values

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mode is selected the values range is 0-1, with 0

indicating no sensor flexure and 1 indicating total

sensor flexure.

Figure 4: Resources Drag & Drop.

Figure 5: BB Drag & Drop.

Figure 6: Tracker behavioural Building Block.

Figure 7: Glove behavioural Building Block.

Figure 8: 3D Visor behavioural Building Block.

The data that can be retrieved by pOuts is, from

left to right:

• Sensor 0 flexure or Sensor A flexure (fig 1)

• Sensor 1 flexure or Sensor A flexure (fig 1)

• Sensor 2 flexure (fig 1)

• Sensor 3 flexure or Sensor B flexure (fig 1)

• Sensor 4 flexure or Sensor B flexure (fig 1)

• Sensor 5 flexure (fig 1)

• Sensor 6 flexure or Sensor C flexure (fig 1)e

• Sensor 7 flexure or Sensor C flexure (fig 1)

• Sensor 8 flexure (fig 1)

• Sensor 9 flexure or Sensor D flexure (fig 1)

• Sensor 10 flexure or Sensor D flexure (fig 1)

• Sensor 11 flexure (fig 1)

• Sensor 12 flexure or Sensor E flexure (fig 1)

• Sensor 13 flexure or Sensor E flexure (fig 1)

• Hand gesture recognition

• Handedness of the glove

• Glove Model Description

• Number of gloves connected

• Type of gloves connected

• Internal latency time, first 32bits

• Internal latency time, last 32bits

3.3 eMagin Z800 Integration

3D Visors has two components to be integrated with

Virtools. The first one is headset orientation given

from its internal gyroscopes and the second one is

stereoscopic visualization to enhance depth

perception.

Headset Orientation - Like in the gloves and

magnetic tracker, a Manager and a behavioural

Building Block, eMaginBB, are created using

Virtools SDK and eMagin SDK. The Manager

handles communication with 3D Visors and

retrieves its orientation data to make it available to

eMaginBB.

There is only one pIn: PollTime. It allows the

programmer to change the time interval in which a

callback function is internally called in the manager

to collect new orientation data from the 3D Visor

device (Figure 8)

The pOuts, from left to right, have the following

data:

• Roll angle

• Pitch angle

• Yaw angle

• Internal latency time, first 32bits

• Internal latency time, last 32bits

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Visualization - Virtools already have a plug-in,

VR-Pack (5DT, 2004), that deals with stereoscopy.

However, a set of external files must be configured

in order to activate stereoscopy into an application.

Also the game camera must be configured in a way

that its view frustum becomes asymmetrical and

provide a correct perception of stereoscopy.

Convergence Plane: Plane where objects left

and right images converge

Parallax: Difference in centimetres between

scenes projected in left and right images

IPD: Interpuppilar distance

Using asymmetrical view frustums cameras

makes the created depth perception effect the most

immersive possible. These special cameras are

known as Projection Referential Cameras and,

instead of using a position, orientation, aspect ratio,

field of view, near and far clips, use a position, 3D

Sprite (eMagin, 2005) and near and far clips. A 3D

Sprite is a basically a 2D image/quad inside Virtools

with a certain position and orientation.

If conventional cameras were used into with

stereoscopy the result would be as shown in Figure

12.

Notice that the convergence plane is located at

the infinite and the parallax is always negative,

meaning that all the objects are perceived before the

convergence plane, which is obviously wrong. A

well balanced stereoscopic image must contain

objects with a negative and positive parallax, so that

they are perceived after and before the convergence

plane. Also some of the objects may have a zero

parallax which indicates that they intercept the

convergence plane.

4 GAME DEVELOPMENT

A brief description will be made about the games

that were developed during this work. A set of core

scripts were created to acquire the data from all the

immersive devices and to configure active

stereoscopy. Both the data from the tracker, glasses

gyroscope and the gloves passes through a simple

software low-pass filter, which minimizes the data’s

high-frequency noise. It calculates an average value

from a pre-defined number of samples taken from

the BB’s TrackerBB, eMaginBB and GloveBlock.

Position and orientation data is retrieved from

the tracker manager into trackerBB (Figure 13). This

data is passed through the filter and a new position

and orientation are calculated and applied to the

desired 3D object to control.

For the data gloves, flexure data passes through a

low pass-filter similar to the one described above, a

flexure variation is then calculated for each sensor

and applied to the virtual hands (Figure 14). If

activated, the player camera position will be

translated accordingly to the value from the gesture

pOut.

The pseudo-code for 3D Visor (Figure 15) is

similar to the magnetic tracker, but it only calculates

an orientation with yaw and pitch angles since roll

angle rotation is not usually used in a camera

orientation.

For the 3D Visor, besides the external

configuration files, the BBs VR Get Config Token,

VR Stereo Settings and VR Set Projection Ref are

used to define the stereoscopy with a custom created

Projection Camera (Nahon et al, 2006).

Two games were created using these core

scripts, PongVR, a table tennis simulator and

PianoVR, a virtual piano.

Figure 9: Correct Stereoscopy.

Figure 10: Standard Camera.

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Figure 11: Projection Referential Camera.

Figure 12: Stereoscopy with standard cameras.

1. Get Position and orientation data

from magnetic tracker

2. Calculate TrackerBB execution time

3. Attenuate high-frequency noise

with low-pass filter

4. Data insertion on a vector with a

pre-defined size

5. Eliminate oldest value if vector

full

6. Calculate an arithmetic average

value from vector data

7. Calculate new orientation

8. Apply new orientation to

hand/racket using local

coordinate system

9. Calculate new position

10. Apply new position to hand/racket

using world coordinate system

Figure 13: Magnetic tracker pseudo code.

1. Obtain gloves flexure data/gloves

gesture

2. Calculate GloveBlock execution

time

3. Attenuate high-frequency noise

with low-pass filter

4. Data insertion on a vector with a

pre-defined size

5. Eliminate oldest value if vector

full

6. Calculate an arithmetic average

value from vector data

7. Calculate flexure variation from

each sensor

8. Apply variations to fingers using

local coordinate system

9. (If active) Apply camera movement

mapped by glove gesture

Figure 14: Glove data pseudo code.

1. Get orientation data from 3D Visor

gyroscope

2. Calculate eMaginBB execution time

3. Attenuate high-frequency noise

with low-pass filter

4. Data insertion on a vector with a

pre-defined size

5. Eliminate oldest value if vector

full

6. Calculate an arithmetic average

value from vector data

7. Calculate new orientation

8. Apply new orientation to active

game camera using local

coordinate system

Figure 15: eMagin gyroscope pseudo code.

Figure 16: Stereoscopy configuration script.

4.1 PongVR

This game’s main goal is to simulate a real table

tennis game. A player uses tracking information to

position and orient a racket in the 3D virtual world:

a 3D Visor is used to visualize the game and orient

the player’s camera using its internal gyroscope. A

5DT glove is put on the player’s left hand with the

purpose of moving the camera with a set of

predefined gestures. The game’s physics simulation

is achieved through Virtools Physics pack. A hit

combo system is also created to enhance the player’s

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gaming experience. Video demonstrations of this

game are publicly available in the youtube

PongVR offers the possibility to configure all

sensors sensibility from within the game, through

the Options Menu accessible in the Start Menu or

pressing ‘P’ during the game. Three difficulty modes

Easy, Medium and Hard are programmed, which

defines the opponent AI.

4.2 PianoVR

In this game the player controls a pair of virtual

hands in order to play a piano. Two tracker receivers

are used, one to each hand, so the player can move

and orient both virtual hands.

Besides the tracker data, a pair of 5DT gloves

are put on and their sensors information are used to

transform a bone system within each of the virtual

hands. Every one of these bones has a weight

associated to determine how the hands mesh will be

modified. The process of creating a bone system,

associating this info into a mesh and transform the

bones is called skinning (Virtools, 2006).

Virtools Physics Pack wasn’t used in PianoVR.

The interaction between hands and piano were

developed specifically to this game. Video demos of

this game may be seen in youtube

The sensibility of all the glove sensors and

tracker may be changed from inside the game using

the Options Menu available from the Start Menu or

pressing ´P ´when in game.

Like PongVR, this game makes use of the 3D

Visor to view the game with active stereoscopy and

to orient the player’s cam.

In order to increase gaming experience, a series

of pre-determined music’s are placed into the game

and the player’s objective is to successfully play

each one of these songs within a limited time. Three

difficulty modes are given to the player, Easy,

Medium and Hard. They define how much time the

player has to perform each one of the predefined

music’s.

5 PERFORMANCE

MEASUREMENTS

A series of tools were created to know how well the

immersive devices behave inside Virtools. A new

http://youtube.com/watch?v=wEDRyzol-J8

http://youtube.com/watch?v=futpUwc2A0A

http://youtube.com/watch?v=PSGD9bRWvWw

http://youtube.com/watch?v=EFJttobtFrU

Manager, Time Manager, along with a new

behavioural Building Block, named

Get_Precise_Time, were developed to access the

internal CPU clock and used to perform time

measurements with a resolution of µ seconds.

The time variable supplied by the BB is the time

elapsed since the activation of the Time Manager

from within Virtools, so the execution time of

GloveBlock or TrackerBB is determined by using a

Get_Precise_Time BB before and after those BB.

Both Glove Manager and Tracker Manager also

calculate their internal latency time. Combining this

information with the one given by

Get_Precise_Time BB, the overall time since the

data is requested to the devices until it is used inside

Virtools can be accurately found.

Figure 17: PongVR Main Menu.

Figure 18: PongVR Combo System.

Figure 19: PianoVR in game footage.

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Figure 20: Finger-piano key collision.

Both games supply latency time information to

the player by pressing ‘1’ key. A population of 100

samples is captured to calculate average values. The

table bellow shows time results obtained executing a

composition with just the devices BB, and with both

games PianoVR and PongVR. The measurements

are made in a laptop with a 1.8GHz Core Duo

processor, 1024 of RAM and an ATI X1600

Mobility Radeon Graphics Card.

PianoVR has a total of 9786 behaviours, 102 3D

objects with a total of 7233 faces and makes use of

5.61 MB of Video Ram and PongVR has a total of

625 behaviours, with 48 3D objects, 9063 faces and

makes use of 4.2 MB of Video Ram. This makes

PianoVR the worst case scenario and it will be used

as a reference.

Magnetic Tracker - The tracker has latency time

value of approximately 34ms which is bigger than

expected since given by (Polhemus, 2005), that sums

a total of 20.67 ms. The time differences is caused

by the filters internal latency time to calculate new

values of position and orientation to its receptors and

the fact of the application running inside Virtools

environment also slightly increases the latency time.

Data Gloves - The gloves overall time sums to a

total of 123µs. Information regarding the sampling

frequency (5ms) is provided in (5DT, 2006) for the 5

sensor model but no information is available

regarding the internal latency time. With such a low

value of overall time means that only USB

communication latency is taken into account and the

glove device provides information even without

having new flexure data available.

Glasses Gyroscope - For the 3D Visor model, a

value of 4ms device latency time and 125Hz

sampling rate is provided in which gives a total of

12ms total latency time. The discrepancy between

the official value and the one obtained through the

eMagin Manager is due to the polling time of 30 ms

by eMaginBB pIn, which is also taken into account.

Also the fact of the application is running inside

Virtools environment slightly increases the latency

time.

6 USER TESTS

Some user tests were made in order to evaluate how

well the PongVR and PianoVR interact with a player

and if they have a good immersive experience.

Each one of the users first learn how each device

operates and then plays both games. In the end a poll

is made in which the player have to give a score

from 1 to 10 to some questions.

The global evaluation for both games is quite

good. All users have felt a good immersive

experience while playing both games, and had a

positive response in how the devices features were

integrated into the games. They had also a

successfully augmented depth perception caused by

active stereoscopy from 3D Visor. However they felt

that both games, especially PongVR, had a high

learning curve mostly caused by the magnetic

tracker behaviour.

New features were added into both games after

the user tests namely:

Possibility to change the eMagin Z800 3D Visor

polling time to increase/decrease its gyroscope

sensibility.

Real time calibration of stereoscopic camera

field of view and distance to the convergence plane

so that a user may adjust these values with the

purpose of enhancing depth perception

Table 1: Devices Performance.

Empty

Scene

PianoVR PongVR

GloveBlock

(µs)

8 345 56

TrackerBB

(µs)

8 970 45

eMaginBB

(µs)

41 80 200

Glove Manager

(µs)

123 123 123

Tracker Manager

One Receiver

(µs)

22000 - 22000

Tracker Manager

Two Receivers

(µs)

33000 33000 -

eMagin Manager

(µs)

54000 54000 54000

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320

Table 2: PongVR Poll questions.

PongVR Total

Answer

[1-10]

Tracker sensitivity

8,5

Tracker readyness

8,8

Trackers features Integration

9,0

3D Visors gyroscope sensitivity

6,8

3D Visors gyroscope readyness

6,8

3D Visors features Integration

Depth perception

Immersive experience

7.5

Gameplay

8,2

Game difficulty

8,3

Game global evaluation

7,8

Table 3: PianoVR Poll questions.

PianoVR Total

Answer

[1-10]

Tracker sensitivity

9,2

Tracker readyness

8, 7

Trackers features Integration

9,2

Gloves sensitivity

8,2

Gloves readyness

8, 3

Gloves features integration

8,5

3D Visors gyroscope sensitivity

6,8

3D Visors features Integration

7,8

Depth perception

6,8

Immersive experience

7,7

Gameplay

8,5

Game difficulty

7,5

Game global evaluation

8,2

7 CONCLUSIONS

The goal of this work was to use professional

developing tools to create games using state of the

art immersive devices. Virtools plugins and internal

scripts were developed in a modular way, so that

they can be reused in other contexts and

applications. The focus of this work applications

were game development, but an industrial

application might have been created instead, e.g. a

virtual car assembly line where the user has a virtual

storage and can grab, translate and rotate parts to

assemble a car prototype.

Game design was seriously taken into account

while developing each one of these games. The

creation of an appealing interface, which gives all

the necessary information to the player without

distracting him from the game objective, was a

constant preoccupation. Both games had a modular

architecture with different threads handling game

logic, physics, etc.

However the devices have several issues that

decrease gameplay. Magnetic tracking device has a

limited range of action and relatively high latency

times. Both the data gloves, 3D Visor and Tracker

are connected via USB cable into the PC so the

player has a confined area of movement restricted by

the several cables.

Nevertheless, both games PianoVR and PongVR

were successfully created allowing the player to

have a very immersive experience while playing not

being limited to traditional input/output devices.

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