Hi Murray,
I agree with Gordon, this seems to be a classical transparent sorting
issue. You could try using the "preserveFace" or "preserveObject"
keywords in the option string to the OpenFlight loader, in order to sort
them separately and not merging into fewer drawables. This may be bad
for performance if you have many helicopters in your scene, but it might
solve your sorting issue.
Regards,
Andreas
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On 2011-02-24 15:40, Tomlinson, Gordon wrote:
Hi Murray
In my experience this looks like a classic transparency sorting
issue/problem when you have objects that have transparency and their
objects bounding volumes intersect,( I would also say this has little
to do with you using open flight)
This happens because for efficiency scene graphs sort transparent
object at a geode level and not at a polygonal level, you find this
has been discussed many time in many places
If you look at you model its likely that you Rotors are in one object
and then the windows/glass in another ( you might have more), is you
the think of their 2 bounding spheres they will be intersecting, so as
you view changes then how that are possibly sorted will change hence
you get the punch through effect you see.
One way to try to minimize this is to try and ensure when you create a
model you don't create overlap transparency that overlap, this can be
challenging to do depending on what you are modeling
(you also have to watch for optimizers in Scenegraphs that try to
chunk like materials and texturing in to one group as this can
artificially introduce overlaps)
You can also try to use a an opaque texture to represent windows/port
holes (do you really need them to be transparent?) to help.
You can create you own render bin that sorts at the triangle level for
these models
*/Gordon Tomlinson/*
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*From:*osg-users-boun...@lists.openscenegraph.org
[mailto:osg-users-boun...@lists.openscenegraph.org] *On Behalf Of
*Murray G. Gamble
*Sent:* Wednesday, February 23, 2011 2:37 PM
*To:* OpenSceneGraph Users
*Subject:* Re: [osg-users] Draw Order/Culling with OpenFlight and
Transparency
Thanks for the suggestion, Chuck.
I've tried this, and do not observe any appreciable improvement in
rendering. I should point out that while the images I provided
highlight the main rotor disc as the offending geometry, there are
numerous other geometry elements (e.g., windows) that cause similar
issues when viewed from various angles.
I've stepped through the OpenFlight loader in debug mode and have
observed that the rotors and windows are both being caught by the
tests therein for translucent images and transparent materials,
respectively. These tests result in the state sets being set as
you've suggested, so it appears that OpenFlight loader is treating
these nodes correctly.
Any other ideas?
Murray
On 2011-02-23, at 1:57 PM, Chuck Seberino wrote:
Murray,
Your rotor is being placed in the Opaque render bin, which is causing
all of the geometry behind it to be culled out. You need to make sure
it is in the transparent bin. You should add these to the stateSet of
the rotors:
stateSet->setRenderingHint(osg::StateSet::TRANSPARENT_BIN);
stateSet->setMode(GL_BLEND, osg::StateAttribute::ON);
HTH,
Chuck
On Feb 23, 2011, at 10:53 AM, Murray G. Gamble wrote:
Hi All,
We have an OpenFlight model of a helicopter that exhibits some
undesirable rendering behaviour in OSG. Specifically, various
parts of the helicopter geometry are being culled and/or rendered
in the wrong order. We do not observe this behaviour when
rendering the same model using Vega Prime. I've attached a couple
of screen captures that exemplify the issues.
Can users with similar experiences provide any suggestions as to
how to avoid these rendering artifacts? Does the model
component/geometry hierarchy need to be modified and/or are there
programmatic things that can be done within our OSG application to
remedy the situation?
I'm using OSG 2.8.0.
Many thanks,
Murray
<CH149-OSG.jpg><CH149-VP.jpg>
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