"Tearing" problem with some VRML scenes 
Author Message
 "Tearing" problem with some VRML scenes

Hi,

Anyone know why some (usually large or wide-area) vrml scenes show "Tearing"
with geometry that's close together?

I'm working on a large scene (10,000 polys at present) that looks great in
Cortona 2/2.1 but shows this tearing effect in both Contact 4.2 and Cosmo
Player 2.1.1. I have been very careful NOT to overlap anything but there is
some geometry which is within 5cm of each other (in a scene a few hundred
metres in size). Numeric precision is set to 3 decimal places.

I have noticed this with other large scenes also. I thought it could be a
video card issue but it seems strange that it works on one vrml browser and
not others!

I'm using a Matrox G400 MAX with the latest drivers and have tried various
combos of screen colour depth, openGL, directX etc.

Anyone with an explanation or remedy?

Regards,
Brian.



Thu, 25 Jul 2002 03:00:00 GMT  
 "Tearing" problem with some VRML scenes
This type of problem is usually related to z buffer depth.
Since it seem you are using a recent card, make sure that "force software
rendering" checkbox is not set in Cosmo and do the equivalent in Contact - You
must use hardware acceleration. If it doesnt change, try setting the
visibilityLimit field in NavigationInfo node to the size of your world - or
slighty larger - so you map the full range of the zbuffer to the size of your
world.

Sylvain Carette
VRML designer-composer

Quote:

> Hi,

> Anyone know why some (usually large or wide-area) VRML scenes show "Tearing"
> with geometry that's close together?

> I'm working on a large scene (10,000 polys at present) that looks great in
> Cortona 2/2.1 but shows this tearing effect in both Contact 4.2 and Cosmo
> Player 2.1.1. I have been very careful NOT to overlap anything but there is
> some geometry which is within 5cm of each other (in a scene a few hundred
> metres in size). Numeric precision is set to 3 decimal places.

> I have noticed this with other large scenes also. I thought it could be a
> video card issue but it seems strange that it works on one vrml browser and
> not others!

> I'm using a Matrox G400 MAX with the latest drivers and have tried various
> combos of screen colour depth, openGL, directX etc.

> Anyone with an explanation or remedy?

> Regards,
> Brian.



Thu, 25 Jul 2002 03:00:00 GMT  
 "Tearing" problem with some VRML scenes
Did you use 3dsMax?  For some reason, when the surface normals are defined
during export, the edges of an object tends to pull in.
I have not found a good solution for this other then making the landscape one
big object.

Christopher
#########################

...and now, a word from our sponser

http://socrates.berkeley.edu/~cperi

#########################



Fri, 26 Jul 2002 03:00:00 GMT  
 "Tearing" problem with some VRML scenes


Quote:
> Did you use 3dsMax?  For some reason, when the surface normals are defined
> during export, the edges of an object tends to pull in.
> I have not found a good solution for this other then making the landscape
one
> big object.

I can't see how this could happen. It doesn't explain why my world works in
Cortona but I get tearing in Contact and Cosmo. Also since then I tried it
on my old 200MMX with a different video card and CosmoPlayer 2.1.1 and there
are no problems!?

Can anyone from Blaxxun or ParallelGraphics shed some light on this?

Regards,
Brian.



Fri, 26 Jul 2002 03:00:00 GMT  
 "Tearing" problem with some VRML scenes
Hi Sylvain,

Thanks for the suggestion. I tried it but unfortunately it had no effect. A
also tried switching my G400 MAX card to 32 bit z-buffer rather than 16 bit.

regards,
Brian.


Quote:
> This type of problem is usually related to z buffer depth.
> Since it seem you are using a recent card, make sure that "force software
> rendering" checkbox is not set in Cosmo and do the equivalent in Contact -
You
> must use hardware acceleration. If it doesnt change, try setting the
> visibilityLimit field in NavigationInfo node to the size of your world -
or
> slighty larger - so you map the full range of the zbuffer to the size of
your
> world.

> Sylvain Carette
> VRML designer-composer


> > Hi,

> > Anyone know why some (usually large or wide-area) VRML scenes show
"Tearing"
> > with geometry that's close together?

> > I'm working on a large scene (10,000 polys at present) that looks great
in
> > Cortona 2/2.1 but shows this tearing effect in both Contact 4.2 and
Cosmo
> > Player 2.1.1. I have been very careful NOT to overlap anything but there
is
> > some geometry which is within 5cm of each other (in a scene a few
hundred
> > metres in size). Numeric precision is set to 3 decimal places.

> > I have noticed this with other large scenes also. I thought it could be
a
> > video card issue but it seems strange that it works on one vrml browser
and
> > not others!

> > I'm using a Matrox G400 MAX with the latest drivers and have tried
various
> > combos of screen colour depth, openGL, directX etc.

> > Anyone with an explanation or remedy?

> > Regards,
> > Brian.



Fri, 26 Jul 2002 03:00:00 GMT  
 "Tearing" problem with some VRML scenes
one other thing you can try.

set the creaseAngle to 1.57 on all of you faces.  Just a thought.

Christopher
#########################

...and now, a word from our sponser

http://socrates.berkeley.edu/~cperi

#########################



Fri, 26 Jul 2002 03:00:00 GMT  
 "Tearing" problem with some VRML scenes
Thanks. Tried it but didn't work. And besides, I'm creating an architectural
development which has a lot of 90 degree angles so setting the creaseAngle
to 1.57 just stuffs the shading ...

Regards,
Brian.


Quote:
> one other thing you can try.

> set the creaseAngle to 1.57 on all of you faces.  Just a thought.

> Christopher
> #########################

> ...and now, a word from our sponser

> http://socrates.berkeley.edu/~cperi

> #########################



Sat, 27 Jul 2002 03:00:00 GMT  
 "Tearing" problem with some VRML scenes
One thing some modelers do is create two surfaces a few millimeters
apart to which different textures are applied.  Take a look through
your scene graph and comment out nodes one at a time and see if
your modeler has played this {*filter*} trick on you.
--
Bob Crispen
crispen at hiwaay dot net

"I'm ashamed to live in a country where white slavers and drug
smugglers go to jail, yet Forth programmers are allowed to walk
the streets as free men." -- Ken "The Snake" Stabler



Sat, 27 Jul 2002 03:00:00 GMT  
 "Tearing" problem with some VRML scenes

Quote:

> Anyone know why some (usually large or wide-area) VRML scenes show "Tearing"
> with geometry that's close together?
>  I have been very careful NOT to overlap anything but there is
> some geometry which is within 5cm of each other (in a scene a few hundred
> metres in size). Numeric precision is set to 3 decimal places.

I always attributed this to machine/software precision problems, ultimately
masquerading as Z-buffer inaccuracy.  My VRML files tend to be normalized
(locations limited between +/- 1),to avoid various scaling/avatar anomalies
which leads to this flashing/tearing phenomenon when I forget to specify
sufficient precision.  Did you check your VRML file to make sure it uses 5+
total digits of precision?  You have surfaces that differ in position only in
the 5th decimal place when normalized.

--
===========================================================================
Tom Brikowski, Geosciences Dept., Univ. Texas at Dallas, Richardson, TX

Learn about our Environmental Program at http://www.utdallas.edu/~brikowi/



Sat, 27 Jul 2002 03:00:00 GMT  
 "Tearing" problem with some VRML scenes
Hi Tom,

I was surprised but this actually worked! I increased numeric precision to 8
digits and although there are some small problem areas it is 95% fixed. The
file size wasn't too badly effected either.

This problem must have something to do with the way the VRML browser
interfaces with the underlying hardware whether that be through DirectX or
OpenGL. It just seems weird that Cortona was fine on the same scene and both
Blaxxun and Cosmo had problems yet on my other machine Blaxxun is fine
(different video card)!

Thanks Tom and everyone for the help!

Regards,
Brian.


Quote:

> > Anyone know why some (usually large or wide-area) VRML scenes show
"Tearing"
> > with geometry that's close together?
> >  I have been very careful NOT to overlap anything but there is
> > some geometry which is within 5cm of each other (in a scene a few
hundred
> > metres in size). Numeric precision is set to 3 decimal places.

> I always attributed this to machine/software precision problems,
ultimately
> masquerading as Z-buffer inaccuracy.  My VRML files tend to be normalized
> (locations limited between +/- 1),to avoid various scaling/avatar
anomalies
> which leads to this flashing/tearing phenomenon when I forget to specify
> sufficient precision.  Did you check your VRML file to make sure it uses
5+
> total digits of precision?  You have surfaces that differ in position only
in
> the 5th decimal place when normalized.

> --

===========================================================================

- Show quoted text -

Quote:
> Tom Brikowski, Geosciences Dept., Univ. Texas at Dallas, Richardson, TX

> Learn about our Environmental Program at http://www.utdallas.edu/~brikowi/



Sun, 28 Jul 2002 03:00:00 GMT  
 
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