Hi
I see my argumentation was a bit short-sighted.
The samplecode is in the attachment, hope this helps.
> You might be able to use the Background node as a workaround
Maybe for this case i used in my sample (Stars in the Background), but there
are other things in my application, which can't be done this way, so leading
me to the same problems.
I already thought about using locales too, and i surely will have to use
them, when i start to model bigger parts of the cosmos.
- emanuel
> > Date: Fri, 15 Nov 2002 14:21:18 +0100
> > From: Emanuel Brzostowski <[EMAIL PROTECTED]>
> >
> > > Moving both viewplatform and object by similar transform will degrade
> > > quality. You should try to keep all objects as close to center as
> > > possible - within 100000 units let say.
> >
> > Exatly this is the point! The only transform i apply is a transform to
> the
> > viewplatform:
> > viewTransform.mul(moveTrans);
> >
> > If we talk about precision, this is the only point, where precision may
> play
> > a role. The multiplication is only numeric, so errors will surely occur
> and
> > accumulate over time. BUT after this, i do no more transformations, i
> just
> > take the translational part out of the viewtransform (-matrix) and
> rebuild my
> > objecttransform:
> > viewTransform.get(viewTranslation);
> > StarsTransform.setTranslation(viewTranslation);
> > StarsTransformGroup.setTransform(StarsTransform);
> > viewTransformGroup.setTransform(viewTransform);
> >
> > So in turn i should have two transforms with should be equal (at least
> in the
> > translational parts). (In fact i tested it, objecttransform and
> > viewtransform ARE equal the whole time in my testcase.) So even if
> java3d
> > would use integers internally, after all the transforms are the same ;)
>
> Because this is a scenegraph, the view transform has to be inverted and
> multiplied with the object transform to get the transform from object
> coordinates to view platform coordinates (and from there to eye
> coordinates and
> projection/clipping coordinates). But since the view and object
> transforms are
> just translations, Java 3D should recognize that all it needs to do is
> subtract
> the translation components.
>
> Bottom line, we can't tell from the code snippets and description you
> provided
> whether this a user error, a problem with scene graph update
> synchronization, a
> transform problem, or some inherent precision limitation. Send us a small
> but
> complete test application that reproduces the problem and we'll be able to
> investigate further.
>
> You might be able to use the Background node as a workaround -- it was
> designed
> to eliminate translation effects, rendering the Background geometry "at
> infinity". And as you noted, the problem is only with large distances, so
> you
> might consider keeping your objects closer to the origin, or investigate
> the
> use of multiple Locales with different origins in high-resolution
> coordinates.
>
> -- Mark Hood
>
>
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package jittertest;
import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
import com.sun.j3d.utils.applet.MainFrame;
import com.sun.j3d.utils.geometry.ColorCube;
import com.sun.j3d.utils.universe.*;
import javax.media.j3d.*;
import javax.vecmath.*;
import java.util.Enumeration;
public class testJitter extends Applet
{
TextField posTxt = new TextField(20);
Transform3D viewTransform;
TransformGroup viewTransformGroup;
Transform3D StarsTransform;
TransformGroup StarsTransformGroup;
public testJitter()
{
setLayout(new BorderLayout());
GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
GraphicsDevice gs = ge.getDefaultScreenDevice();
GraphicsConfigTemplate3D devconfig = new GraphicsConfigTemplate3D();
GraphicsConfiguration config = gs.getBestConfiguration(devconfig);
Canvas3D c = new Canvas3D(config);
add("Center", c);
Panel infoPanel = new Panel();
infoPanel.setLayout(new FlowLayout());
Label posLabel = new Label("viewer pos:");
infoPanel.add(posLabel);
infoPanel.add(posTxt);
add("South", infoPanel);
VirtualUniverse myUniverse = new VirtualUniverse();
Locale myLocale = new Locale(myUniverse);
myLocale.addBranchGraph(buildViewBranch(c));
}
public BranchGroup buildViewBranch(Canvas3D c)
{
BranchGroup viewBranch = new BranchGroup();
viewTransform = new Transform3D();
viewTransformGroup = new TransformGroup(viewTransform);
ViewPlatform myViewPlatform = new ViewPlatform();
// adding a colorcube infront of the viewer
StarsTransform = new Transform3D();
StarsTransformGroup = new TransformGroup(StarsTransform);
StarsTransformGroup.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
Transform3D sunTransform = new Transform3D();
sunTransform.set(new Vector3d(0.0, 0.0, -10.0));
TransformGroup SunTG = new TransformGroup(sunTransform);
SunTG.addChild(new ColorCube());
StarsTransformGroup.addChild(SunTG);
viewTransformGroup.addChild(myViewPlatform);
timedBehavior behav = new timedBehavior();
behav.setSchedulingBounds(new BoundingSphere(new Point3d(0.0, 0.0, 0.0), 1000.0));
viewTransformGroup.addChild(behav);
viewTransformGroup.setCapability(TransformGroup.ALLOW_TRANSFORM_READ);
viewTransformGroup.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
viewBranch.addChild(viewTransformGroup);
viewBranch.addChild(StarsTransformGroup);
View myView = new View();
PhysicalBody myBody = new PhysicalBody();
PhysicalEnvironment myEnvironment = new PhysicalEnvironment();
myView.setPhysicalBody(myBody);
myView.setPhysicalEnvironment(myEnvironment);
myView.addCanvas3D(c);
myView.attachViewPlatform(myViewPlatform);
return(viewBranch);
}
public static void main(String[] args)
{
System.out.println("By pressing any key, the view is translated in neagtive z by
1000 units continuosly.");
System.out.println("After a short time, the cube (moving together with the viewer)
begins to jitter.");
System.out.println("Jitter gets worse the farther the view departs form the
origin. ");
new MainFrame(new testJitter(), 512, 512);
}
/////////////////////////////////////////////////////////////////
// Inner Classes
/////////////////////////////////////////////////////////////////
public class timedBehavior extends Behavior
{
public boolean running = false;
WakeupCriterion[] wakeConditions;
WakeupOr oredConditions;
AWTEvent ae[];
Transform3D moveTrans;
Vector3d viewTranslation;
public void initialize()
{
moveTrans = new Transform3D();
moveTrans.set(new Vector3d(0.0, 0.0, -1000.0));
viewTranslation = new Vector3d();
wakeConditions = new WakeupCriterion[3];
wakeConditions[0] = new WakeupOnAWTEvent(KeyEvent.KEY_PRESSED);
wakeConditions[1] = new WakeupOnAWTEvent(KeyEvent.KEY_RELEASED);
wakeConditions[2] = new WakeupOnElapsedTime(10);
oredConditions = new WakeupOr(wakeConditions);
wakeupOn(oredConditions);
}
public void processStimulus(Enumeration criteria)
{
WakeupCriterion theCriteria;
if(criteria.hasMoreElements())theCriteria =
(WakeupCriterion)criteria.nextElement();
else
{
wakeupOn(oredConditions);
return;
}
if(theCriteria instanceof WakeupOnAWTEvent)
{
ae = ((WakeupOnAWTEvent)theCriteria).getAWTEvent();
if(ae[0].getID()==KeyEvent.KEY_PRESSED) running = true;
else if(ae[0].getID()==KeyEvent.KEY_RELEASED) running = false;
}
else
{
if(running&&(theCriteria instanceof WakeupOnElapsedTime))
{
viewTransform.mul(moveTrans);
viewTransform.get(viewTranslation);
StarsTransform.setTranslation(viewTranslation);
StarsTransformGroup.setTransform(StarsTransform);
viewTransformGroup.setTransform(viewTransform);
posTxt.setText(viewTranslation.toString());
}
}
wakeupOn(oredConditions);
}
}
/////////////////////////////////////////////////////////////////
}
