Hi Kelvin:
I'm sorry to have troubled you regarding this ... I now don't think Java3D
can help us ... I think it's a known issue with 3D graphics generally
(related to Z-buffer fighting / coplanar primitives). I had no luck with
polygon offsets/factors, as when you rotate an object, you will still get
the problem at some orientation. Thanks for pointing me in the right
direction though ...
Regards,
Geoff
----- Original Message -----
From: "Kelvin Chung" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Sent: Saturday, April 28, 2001 2:48 AM
Subject: Re: [JAVA3D] Sun help! Joined Shapes With Lighting Problem
>
> >MIME-Version: 1.0
> >Content-Transfer-Encoding: 7bit
> >X-Priority: 3
> >X-MSMail-Priority: Normal
> >X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4522.1200
> >Date: Fri, 27 Apr 2001 15:43:38 +0800
> >From: Geoff Morris <[EMAIL PROTECTED]>
> >Subject: Re: [JAVA3D] Sun help! Joined Shapes With Lighting Problem
> >Comments: To: Kelvin Chung <[EMAIL PROTECTED]>
> >To: [EMAIL PROTECTED]
> >
> >Thanks Kelvin, for investigating this for us ...
> >
> >> I can see when the program startup, there is two small
> >> black line in the initial orientation. Moving the cylinder
> >> around will sometime see the artifact (under windows).
> >>
> >
> >It's much worse here, as there are perhaps 50 unwanted dots / dotted
lines,
> >although some orientations are better (Windows 98; i810; OpenGL 1.1 or
> >DirectX 8, Java3D 1.2.1).
> >
> >> Under solaris, it works fine. Probably because
> >> a combination of numerical precision, opengl and
> >> graphics card give more precise location where
> >> the disc render.
> >>
> >
> >It's good news that it works somewhere, as it gives us something to work
> >with. I think that you're suggesting that it isn't Java3D's issue, in
that
> >it's an OpenGL/DirectX/graphics card problem? I guess this means that
the
> >lighting calculations occur outside of Java3D, and that Java3D just
passes
> >the geometry coordinates and vertex normals on. I'm showing my lack of
> >understanding ... Java3D is my first contact with 3D graphics
development,
> >and OpenGL and DirectX are currently 'black magic' to me.
> >
>
> Actually it also shown up upon more testing but less obvious.
> The problem is that the edges in the connection are overlapping
> using the same z depth value.
>
> >> To workaround this numerical problem, you
> >> can add an small offset to create a disc
> >> with longer length. Then add polygon offset between
> >> alternative disc to avoid z buffer fighting for
> >> the small overlap portion.
> >>
> >
> >I had tried this but it's no help. Actually, we've discovered that by
> >removing the ends of the joining shapes then that works (unattractive but
> >it's a possible option).
> >
> If you are using DirectX version, only negative z offset is support,
> positive z offset are ignored.
>
> - Kelvin
> ------------
> Java 3D Team
> Sun Microsystems Inc.
>
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