I am pretty sure ZBuffer detection happens during rasterization. Thus it is
not until you get to the pixel level that the depth value is checked. I am
pretty sure this is done on the card and not in Java3d since they just hand
geometry to the card for processing. I am also pretty sure that a single
polygon spanning a large number of pixels and depth values will be rendered
correctly assuming it is within tolerance of the ZBuffer.
Dave
----- Original Message -----
From: John Wright <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, May 08, 2001 7:21 AM
Subject: Re: [JAVA3D] Grafic card question
Desiree,
That's my understanding too... for WinNT 4.0 your only choice is OpenGL.
So it sounds like an issue that existed but changing the video card made
the issue more noticable. Is there any chance you changed the color
depth you are using too?
Yes, I would consider your geometry large. Looking at your points there
are differences of over 800. Perhaps Sun could comment on this more, but
800 is likely to be greater than the distance from front to back clip
and from my own observations I'd question exactly how Java 3D (or
OpenGL) calculates the "Z" value for each pixel on a surface like that.
Does Java 3D calculate a single depth value for a polygon? It seems to
me that the calculations would be astronomically complex if every pixel
on a polygon actually had a depth calculated. Thus two long flat
surfaces that are separated by a very small distance become difficult to
display properly. I'm just guessing at this from my observations, it
would be nice if a Sun Engineer could explain more of what problems
there might be in using two very large surfaces (single polygon)
separated by a small distance.
- John Wright
Starfire Research
Desiree Hilbring wrote:
>
> >
> > You might want to clarify if you are using Java 3D OpenGL or DirectX.
>
> I am using OpenGL (as far as I know DirectX is not supported for NT?)
>
> > Also did you just swap the video card or did you re-install the video
> > drivers?
>
> I uninstalled the old driver and installed the driver shipped with the new
> card.
>
> Also it's not clear from your e-mail if the problem is worse
> > or better than before... sounds like it wasn't perfect originally.
>
> Ok it was not perfect before, but it is worse now.
>
> >
> > All that being said... I'm wondering if you are seeing a ZBuffer issue.
> > Are your ground terrain and water table polygons very big?
>
> What are you considering as very big?
> These are some sample points, from which my layers are created:
>
> x[m] y[m] z[m]
> 3566390 5474900 around 300m (between 300 and 305m)
> 3566610 5474565
> 3566120 5474500
> 3566930 5474450
> 3566950 5474340
>
> Thanks Desiree
>
> >
> > - John
> >
> > Desiree Hilbring wrote:
> > >
> > > Hi everybody,
> > >
> > > my Elsa Erazor X (Nvidia Geforce Chip) crashed this morning, now I
have a
> > > Elsa Gladiac Geforce 2 MX. The performance is okay.
> > > My problem is the following:
> > > I am creating several layers, say one terrain layer and a second
ground
> > > water table label. Without scaling they height difference between them
is
> > > very small, and then both layers a rendered it looks like one triangle
> > > terrain the other water, while the terrain is really above the water,
I
> > > only want to see the terrain, I did not use transparency or anything
else.
> > > With the Elsa Erazor X I had sometimes the effect the a whole part of
the
> > > object was rendered wrong, but not any triangle different.
> > >
> > > Any hints?
> > >
> > > Thanks for your help in advance
> > >
> > > Desiree
> > >
> > > PS: I am working on NT4 Service Pack 6 with JDK1.3 and Java3D 1.2
> > >
> > >
o------------------------------------------------------------------------o
> > > | Desiree Hilbring Institut fuer Photogrammetrie und
Fernerkundung |
> > > | Universitaet Karlsruhe, Germany
|
> > > |
|
> > > | email: [EMAIL PROTECTED]
|
> > > | # 0721 6083676
|
> > >
o------------------------------------------------------------------------o
> > >
> > >
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> >
> >
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> >
>
>
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