From: Pablo Figueroa [pfiguero@cs.ualberta.ca]
Sent: Wednesday, November 29, 2000 7:01 PM
To: Doug Bowman
Cc: 3dui List; Rex Hartson
Subject: Re: notation for 3D interaction techniques

Hi all,

I'm working on a high level language for interaction techniques (IT) as
part of my PhD. Its main characteristics are:
- It is independendent of any implementation language (i.e. VRML, C++,
Java), but it can be implemented in any of them.
- It defines the interface of each IT and how they can collaborate with
others in an application, so it is possible to describe composition of
ITs.

Unfortunately I don't have yet a published paper to refer to, but I can
make a brief description here, and more details can be found in my website
under "ITLib". The basic idea is that ITs are described as filters with an
internal state, multiple inputs, and multiple outputs. The semantics is
described (so far) in plain english, but I want to try also a more formal
approach with the Object Constraint Language Specification (OCL), part of
the Unified Modeling Language (UML) standard. The language is based on XML
and a short description of the GoGo interaction technique is as follows: 

<class name="GoGoIT" inherits="IT" >
  <comment> // IT Description </comment>
  <iport name="iportHand"></iport>
  <iport name="iportHead"></iport>
  <oport name="virtualHandLocation"></oport>
  <oport name="selectedObject"></oport>
  <meth name="processImpl"></meth>
  <attr name="K" type="float"></attr>
  <attr name="D" type="float"></attr>
  <attr name="relativeChestPos" type="Point3D"></attr>
  <attr name="scene" type="Scene"></attr>
  <attr name="handRepr" type="SceneObject"></attr>
  <attr name="cube" type="SceneObject"></attr>
</class>

This says that GoGo has to inputs (head and hand positions), two outputs
(the virtual hand position and the selected object), and a method to
computer its output (processImpl). This allows GoGoIT to connect in a
dataflow with other ITs in the environment.

The state for GoGoIT is composed of three parameters (K, D, and the
relative chest position from the head) and three objects: the scene (in
order to look for a selected object), a hand representation, and a cube
that will show the real hand's position. The comment can be Doug's
description (or even the orieginal paper one), or also something more
formal like this: (my first draft...  ;-> ) 

==========================
-- The invariant of GoGoIt is as follows
context GoGoIT inv:

-- some variables for the expression that follows
let headPos : Point3D = iportHead.lastValue()
let handPos : Point3D = iportHand.lastValue()
let chestPos : Point3D = headPos + relativeChestPos

-- if the position of the virtual hand is different that the real hand,
-- show the cube.
if( chestPos.distanceTo( handPos ) < D )
  cube.isVisible = false;
else
  cube.isVisible = true;

-- The cube is always in the real hand position
cube.position = handPos
-- The virtual hand is always in the last computed position
handRepr.position = virtualHandLocation.lastOutput()


-- Now the output is computed as follows
context GoGoIT::processImpl 
-- if there is any input ...
  pre: 
       iportHead.newValue() || iportHand.newValue()
-- the output is computed as follows
  post:
       if( chestPos.distanceTo( handPos ) < D )
         virtualHandLocation.lastOutput() = handPos
       else
         -- R comes from Poupyrev's paper...
         let dir : Vector = (handPos - chestPos).unitVector()
         virtualHandLocation.lastOutput() = handPos + dir * K(R - D)^2

       selectedObject.lastOutput() = scene.GetSelectedByTouching(handRepr)
==========================

OCL is based on an object oriented description of a model, so it can use
any OO type and their methods. The specification is at 
http://www.rational.com/uml/resources/documentation/index.jsp

I prefer to read Doug's description, but I'm sure something like the
second one is easier to implement... :)

If anyone is interested, I'd be glad to give more details. I'm also
willing to participate in an group to work on this topic.

Best Regards,

-------------------------------------------
Pablo Figueroa              pfiguero@cs.ualberta.ca
PhD Student                 http://www.cs.ualberta.ca/~pfiguero
University of Alberta

Relax ... God is in charge  
-------------------------------------------