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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