This is a good summary of the 1.1.2 implementation. It is
completely different in 1.2. There is no longer any collision
thread.
Doug Twilleager
Java 3D Team
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> Subject: Re: [JAVA3D] Type of collision detection
> To: [EMAIL PROTECTED]
>
> Sunny,
>
> I'm covering Java 3D collision detection in my book "Java 3D Programming".
> The last chapter is titled "Java 3D System Architecture" and covers these
> kind of topics. Here are some initial thoughts.
>
> Collision detection is implemented in a Thread called
> "J3D-Collision-#instance".
>
> The Collision thread is created by the BehaviorScheduler. The
> BehaviorScheduler is created in the VirtualUniverse constructor, so there is
> one CollisionThread per VirtualUniverse.
>
> The CollisionThread is much like the other threads that Java 3D creates,
> they are switched between waiting and notified using Object.wait() and
> Object.notify() (to switch the threads on and off, so they are not free
> running and chewing up resources).
>
> When the CollisionThread is notified (started) it iterates through the
> Locales in the VirtualUniverse and traverses each of the top-level
> BranchGroups in each Locale.
>
> Basically the Collision detection itself just walks down the scene tree
> checking the bounds on each Group until it finds a Group that does not
> intersect with the object it is currently checking (quick exit). Recursive
> calls will be generated depending on the kinds of Nodes it hits (e.g. it
> will follow Links etc.)
>
> The objects that it checks come from the Arming paths from all the WakeupOn*
> behaviors that have been added to the scenegraph.
>
> If it hits a leaf node (e.g. Shape3D) it does this:
>
> [...]
> if(shape3dretained.collisionBound == null)
> renderobject.vwcBounds.getWithLock(targetBoundsBox);
> else
> renderobject.collBoundsVwc.getWithLock(targetBoundsBox);
> if(targetBoundsBox == null || collidableobject.compareBounds ==
> null)
> return false;
> boolean flag9 =
> targetBoundsBox.intersect(collidableobject.compareBounds);
> if(flag9)
> {
> if(collidableobject.boundsOrGeometry == 1)
> if(collidableobject.geometry == null)
> flag9 =
> ((GeometryArrayRetained)shape3dretained.geometry.mirrorGeometry).intersect(r
> enderobject.localToVWorld, collidableobject.compareBounds);
>
> [...]
>
> Which basically gets the bounds to the object, or generates bounds from
> geometry (converted so they can be compared), and calls "intersect" on the
> bounds of the collision object we are testing.
>
> When the traverse is done, the thread goes back to sleep with a call to
> Object.wait()... maybe!.
>
> I'm no expert on collision detection, but this seems like a pretty "basic"
> implementation from an algorithm point-of-view. I may also have missed some
> complexity in the Java 3D code (I need to examine it some more), so
> apologize all round if I have mis-stated anything. Please note that all this
> is based on the current implementation of Java 3D.
>
> I hope this gives some insights, if not much help!
>
> Sincerely,
>
> Daniel Selman
>
> [EMAIL PROTECTED]
> http://www.tornadolabs.com
>
>
> -----Original Message-----
> From: Discussion list for Java 3D API
> [mailto:[EMAIL PROTECTED]]On Behalf Of Tony Burrows
> Sent: 14 October 1999 15:34
> To: [EMAIL PROTECTED]
> Subject: Re: Type of collision detection
>
>
> At 11:52 11/10/99 +1000, you wrote:
> >Hi,
> >
> >Does anybody know what kind of collision detection routines are being
> >implemented in the Java 3D collision detection behavior (i.e.,
> >WakeupOnCollisionEntry(), WakeupOnCollisionExit() and
> >WakeupOnCollisionMovement()).
> >
> >Many thanks,
> >regards,
> >Sunny Leung
> >
> >===========================================================================
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> >
> >
> I've seen nothing about it generally Sunny. There was a report some time
> ago that it is running in a seperate, inaccessible, thread - but that's
> been the only comment I've seen on it. There have been a lot of criticisms
> about where it fails to work, so it wouldn't seem to be one of the standard
> ones.
>
> I've heard, via the team who brought us VCollide, a rumour that there are
> supposed to be teams in Japan and Australia working on a Java version of
> this and another that a team is working on a Java version of VClip.
>
> Tony
> Microsoft is not the answer.
> Microsoft is the question.
>
> Avoid the Gates of Hell. Use Linux
>
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