VR Juggler 1.0 Application Programming

1
VR Juggler 1.0Application Programming

• Patrick Hartling
• Virtual Reality Applications Center
• IEEE VR 2002

2
Objectives

• Learn VR Juggler programming basics
• Be able to write VR Juggler applications
• Please Ask questions!!!

3
Overview

• Application objects
• VR Juggler utility classes
• Simple VR Juggler application
• Advanced OGL application

4
Online Documentation

• www.vrjuggler.org
• Projects
• VR Juggler
• Documentation
• Guides and references

5
Application Objects

• All VR Juggler applications are objects
• Override methods of a pre-defined interface
• Derived class for each graphics API
• No main() Dont call me, Ill call you
• Kernel controls application by calling methods

6
Application Objects

• Application object is derived from graphics API
  specific base class
• User application methods must fill-in-the-blank

7
VR Juggler main()
include ltsimpleApp.hgt int main (int argc, char
argv) // Get kernel vjKernel kernel
vjKernelinstance() simpleApp app new
simpleApp() // Create app obj
kernel-gtloadConfigFile() // Configure kernel
kernel-gtstart() // Start kernel
thread kernel-gtsetApplication(app) // Give app
to kernel while ( ! exit ) // sleep

• How VR Juggler starts-up

8
VR Juggler main()
include ltsimpleApp.hgt int main (int argc, char
argv) // Get kernel vjKernel kernel
vjKernelinstance() simpleApp app new
simpleApp() // Create app obj
kernel-gtloadConfigFile() // Configure kernel
kernel-gtstart() // Start kernel
thread kernel-gtsetApplication(app) // Give app
to kernel while ( ! exit ) // sleep

• Get handle to kernel

9
VR Juggler main()
include ltsimpleApp.hgt int main (int argc, char
argv) // Get kernel vjKernel kernel
vjKernelinstance() simpleApp app new
simpleApp() // Create app obj
kernel-gtloadConfigFile() // Configure kernel
kernel-gtstart() // Start kernel
thread kernel-gtsetApplication(app) // Give app
to kernel while ( ! exit ) // sleep

• Create the application
• Instance of users application object

10
VR Juggler main()
include ltsimpleApp.hgt int main (int argc, char
argv) // Get kernel vjKernel kernel
vjKernelinstance() simpleApp app new
simpleApp() // Create app obj
kernel-gtloadConfigFile() // Configure kernel
kernel-gtstart() // Start kernel
thread kernel-gtsetApplication(app) // Give app
to kernel while ( ! exit ) // sleep

• Give the kernel initial configuration files
• Start the kernel thread
• VR Juggler is now fully running

11
VR Juggler main()
include ltsimpleApp.hgt int main (int argc, char
argv) // Get kernel vjKernel kernel
vjKernelinstance() simpleApp app new
simpleApp() // Create app obj
kernel-gtloadConfigFile() // Configure kernel
kernel-gtstart() // Start kernel
thread kernel-gtsetApplication(app) // Give app
to kernel while ( ! exit ) // sleep

• Give the kernel an application to run
• Kernel now starts calling the application
  objects methods

12
Application Object Methods

• Initialization
• init() Application initialization
• Ex Loading data files, lookup tables
• apiInit() Graphics API specific initialization
• Ex scene graph loading
• Frame functions
• preFrame() Called at start of frame
• Ex Updating data in response to device input
• intraFrame() Called while rendering
• Ex Time consuming computation for next frame
• postFrame() Called after frame is done
• Ex Clean up, sync with external net or compute

13
Application Interface

• Other
• Reconfiguration
• Reset
• Exit
• Focus change

14
Call Timing
include ltsimpleApp.hgt int main (int argc, char
argv) // Get kernel vjKernel kernel
vjKernelinstance() simpleApp app new
simpleApp() // Create app obj
kernel-gtloadConfigFile() // Configure kernel
kernel-gtstart() // Start kernel
thread kernel-gtsetApplication(app) // Give app
to kernel while ( ! exit ) // sleep

• setApplication() starts the kernel calling the
  applications member functions

15

• Call timing Init members
• init()
• Called after kernel gets app
• apiInit()
• Called after graphics API is running

16

• Call timing Frame members
• preFrame()
• Called after input update
• intraFrame()
• Called while rendering of environment is
  happening
• postFrame()
• Called after frame but before tracker updates

17
vjGlApp OpenGL Application Interface

• Derived from vjApp
• OpenGL specific extensions
• draw()
• Draw the scene in OpenGL
• Called for each OpenGL context
• Stereo ? Called once per eye
• contextInit(), contextPreDraw(), contextClose()
• Discussed later

18
vjPfApp PerformerApplication Interface

• Derived from vjApp
• Performer specific extensions
• initScene()
• Create the scene graph
• getScene()
• Return the root of the scene graph

19
Common Classes

• Helper classes needed for app development
• Mathematics matrix, vector, point
• Input devices

20
Common Classes vjMatrix

• 4x4 matrix
• OpenGL ordering
• Methods
• Rotation makeXYZEuler(), makeRot()
• Translation makeTrans(), setTrans()
• Multiplication mult(), preMult(), postMult()
• Many others (see Programmers Guide)

21
Common Classes vjVec3 vjVec4

• Class for float vector
• Used for points and rays
• Methods
• ,-,
• dot(), normalize(), cross()
• Many others (see Programmers Guide)

22
Common Classes vjProxy

• Proxies are used to access all input data
• wand_pos mWandProxy-gtgetData()
• Proxies cache and transform input data

23
Common Classes vjDeviceInterface

• Used to get access to devices through proxies
• Smart pointer to a device proxy
• Makes proxies easier to use
• init()
• mWand.init(VJWand)

24
Common Classes vjPosInterface

• vjPosInterface
• Used to get positional information.
• Ex. trackers, wand position, head position
• Derived from vjDeviceInterface
• Dereferences to vjPosProxy
• operator(), operator-gt()
• Get proxy data with getData()
• vjMatrix wand_pos
• wand_pos mWand-gtgetData()

25
Common Classes vjDigitalInterface

• vjDigitalInterface
• Used to get digital information (ie. 0 or 1)
• Ex wand buttons
• getData() returns integer
• States (return value)
• OFF
• ON
• TOGGLE_ON Just switched to on state
• TOGGLE_OFF Just switched to off state

26
Sample Application 1Simple OpenGL Application
simpleApp
27
Sample Application 1 simpleApp

• Simple OpenGL drawing app
• Member function
• vjAppinit()
• vjGlAppdraw()
• Files
• simpleApp/simpleApp.h, simpleApp/simpleApp.cpp

28
simpleApp Data Members
class simpleApp public vjGlApp public
simpleApp() virtual void init() virtual
void draw() public vjPosInterface mWand
vjPosInterface mHead vjDigitalInterface
mButton0 vjDigitalInterface mButton1

• mWand, mHead
• Position interface to positional proxy
• Get position
• vjMatrix wand_pos
• wand_pos (mWand-gtgetData())
• mButton0, mButton1
• Digital interface to digital proxy
• if(mButton0-gtgetData())
• cout ltlt Button Pressed

29
simpleApp init()

• Initialize device interface
• Device name
• From configuration file
• Name of device alias or proxy

void simpleAppinit() // Initialize
devices mWand.init(VJWand)
mHead.init(VJHead) mButton0.init(VJButton0
) mButton1.init(VJButton1)
30
simpleApp draw()
void simpleAppdraw() ... // Create box
offset matrix vjMatrix box_offset
box_offset.makeXYZEuler(-90,0,0)
box_offset.setTrans(0.0,1.0f,0.0f) ...
glPushMatrix() // Push on offset
glMultMatrixf(box_offset.getFloatPtr())
... drawCube() glPopMatrix() ...

• Create an offset matrix
• Draw cube

31
Sample Application 2OpenGL Application with
Context-Specific Data
contextApp
32
Context-Specific Data

• What is a Context?
• OpenGL Window ? Context for OGL state machine
• What is context-specific data?
• Display lists, texture objects, etc.
• Why do you need it?
• VR Juggler uses a single memory pool for all
  threads
• All threads have access to the same variables
• Ex Multi-wall system

33
Context-Specific Data

• How does it work
• Template-based smart pointer class
• Dereference like normal pointer
• ie. operator(), operator-gt()
• vjGlContextDataltGLuintgt myDispList
• ( myDispList) glGenList(1)
• glCallList(myDispList)

34
Context App Data Members
Class contextApp public vjGlApp public
contextApp() virtual void init() virtual
void contextInit() virtual void draw()
public // Identifier for the cube display
list vjGlContextDataltGluintgt mCubeDlId

• Context-specific data for a display list that
  draws a cube

35
Context App contextInit()

• Create display list
• Context-specific version is used

void simpleAppcontextInit() // Allocate
context specific data (mCubeDlId)
glGenLists(1) glNewList((mCubeDlId),
GL_COMPILE) glScalef(0.50f, 0.50f,
0.50f) drawCube() glEndList() ...
36
Context App draw()
void simpleAppdraw() // Get Wand matrix
vjMatrix wand_matrix wand_mat
(mWand-gtgetData()) ... glPushMatrix()
glPushMatrix() glMultMatrixf(wand_mat
.getFloatPtr()) glCallList(mCubeDlId)
glPopMatrix() ... glPopMatrix()

• Render display list
• De-reference context-specific display list ID

37
Conclusion

• Questions?