Creating Virtual Reality
Applications Using FreeVR
David J. Zielinski
djzielin@duke.edu
Friday Visualization Forum
October 1st,2004
Overview
1) What is Virtual Reality?
2) What are my choices?
3) Why use FreeVR?
4) FreeVR program outline
5) Application demos
1) What is Virtual Reality?
What is Virtual Reality?
●
●
Physically immersive (generate input to
user's sensory systems)
Interactive (user can change the
experience)
Examples:
reading a book (not interactive or immersive)
video game (interactive but not immersive)
3-d movie (immersive but not interactive)
What can we use for physically
immersive?
●
3-d vision
– projection
systems: [anaglyphic
(red/blue), polarized, active stereo]
– head
mounted displays.
What can we use for physically
immersive?
●
3-d sound
– multichannel
– Headphone
speaker setups
simulation
What can we use for physically
immersive?
●
Other:
– Touch/force
feedback
– Taste
– Smell
– Environmental
conditions
(temperature)
– Accelerations/motion
– Direct
connection to human nervous
What can we use for
interactive?
• location tracking systems: magnetic, video,
ultra-sonic
What can we use for
interactive?
• joysticks: wands, game controllers
• other: gloves, eye tracking, biological
indicators (heart-rate, breathing), props
(steering wheels, fishing poles)
2) What are my choices for
developing an
application/experience?
A) Write from scratch
B) Low-level library
C) Medium-level library (scenegraph)
D) High-level graphical program
E) Use domain-specific, off the shelf
program
Write from scratch
●
Pro:
– complete
control
– maximum
performance/speed
possible
●
Con:
– Long,
difficult development
– Often
device dependent
Low-level library
(CAVELib, FreeVR, DIVERSE)
●
Pro:
– lots
of control (C/C++,OpenGL
programming)
– device
●
independent
Con:
– difficult
– more
for non-programmers,
control/freedom than most
applications require
Medium-level library
(OpenSceneGraph, Performer)
Medium-level library
(OpenSceneGraph, Performer)
●
Pro:
– built
in algorithms to cull (eliminate)
non-viewable objects
– built
in algorithms for collision
detection
●
Con:
– Still
lots of programming
– learning
curve to use scenegraph
High-level graphical program
(Virtools)
High-level graphical program
(Virtools)
●
Pro:
– Easy
visual design of worlds
– Visual,
flow design for object
behaviors
●
Con:
– Expensive
– speed/performance?
– Still
have to learn to “program”
Use domain-specific, off the
shelf program (Amira, VMD)
Use domain-specific, off the
shelf program (Amira, VMD)
●
Pro:
– Very
easy, especially if group is
already using non-VR version of
program
●
Con:
– Individual
– not
configuration
applicable to making custom
applications
3) Why use FreeVR?
●
device independence (input and output)
●
free/opensource (CAVELib is not)
●
●
actively developed (cluster support
soon)
I know how to configure it
How does it become device
independent?
●
●
configuration file (.freevrrc) maps
buttons, sensors, and screen locations
to FreeVR internals. Different physical
configurations require different .rc
settings.
on startup FreeVR opens all necessary
windows, and handles projection
matrices, so correct view is on correct
screen.
abstraction of buttons:
int
pressed=vrGet2switchValue(which_button)
;
if(pressed)
printf(“user pressed the button!”);
abstraction of location sensors:
vrPointGetRWFrom6sensor(&wand_locpnt,
WAND_SENSOR);
float x,y,z;
x=wand_locpnt.v[0];
y=wand_locpnt.v[1];
z=wand_locpnt.v[2];
if((x<...) AND (y<...) AND (z<...))
/* we are touching an object, do something
*/
abstraction of display space:
we provide single function, that is called for
each frame, for each render window.
void draw_world()
{
clear_screen
glTranslatef(0,5,-5); /* real world
coordinates
draw_object
}
4) FreeVR program Outline pt.1
Main(){
initialization calls
setup callback of world render function
setup callback of gfx initialization
while(!terminate){
vrFrame();
update(); /* next slide */
}
}
FreeVR program Outline pt.2
Update(){
check buttons
check sensor positions
do logic
}
draw_world(){
look at world settings (modified in update)
make openGL calls to render world
}
FreeVR programming Subtleties
●
●
Rendering and updates occur in separate
processes, so shared memory is needed.
FreeVR includes vrShmemAlloc0 which is
comparable to malloc. Typically a world data
structure is created, modified, and passed
around.
because of the separate processes we need
to lock the world data when we are writing
and reading it. FreeVR includes vrLock. We
can call vrLockReadSet(the_lock);
vrLockReadRelease(the_lock);
5) Applications –PDB viewer
Virtual Vibraphone
FreeVR Download
http://www.freevr.org/
David J. Zielinski
djzielin@duke.edu