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osgvolume multipass (hybrid geometric/volumic) bug...?


 
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mp3butcher (Julien Valentin)
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Joined: 17 Feb 2010
Posts: 337

PostPosted: Sun Mar 05, 2017 5:04 pm    Post subject:
osgvolume multipass (hybrid geometric/volumic) bug...?
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Hi Robert et al

It's been a while I use a customized osgVolume::MultipassTechnique and experienced a bug I think was coming from my code but in fact it affect osgvolume application too.
to reproduce
Code:
osgvolume image --multipass --model cessna.osg

There are artifacts when rotating the view such as
1)models out of volume tend to disappears (experienced in osgvolume ex rotating the view-when cessna comes out of the hull 2D projection-)
2)models duplication (one is deformed and shouldn't be there)



I would like to debug but would like to be sure how it work,
I tend to understand the following, stop me if I'm wrong:
1/VolumeScene children (except tiles) is rendered as in depth and color textures in prerender pass
2/Tiles backface then Frontface Cube are rendered to determine per pixels ray lengths and then per pixel numiterations ( so rays are casted in FrontFaceCube pass)

It's been a while I haven't dive in there. Can you tellme if I'm wrong and give me directions of what could possibly go wrong in the current MultipassTechnique...

Thank you!

Cheers,
Julien


Last edited by mp3butcher (Julien Valentin) on Mon Mar 06, 2017 12:16 am; edited 1 time in total
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mp3butcher (Julien Valentin)
Appreciator


Joined: 17 Feb 2010
Posts: 337

PostPosted: Sun Mar 05, 2017 11:40 pm    Post subject:
Re: osgvolume multipass (hybrid geometric/volumic) bug...?
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I...have achieved something...
I removed line 394 in VolumeScene.cpp
Code:
viewData->_backdropSubgraph->accept(*cv);

and it works for me
but I can't tell if it's good.... A few doc on the underlying osgvolume design would be cool...



mp3butcher wrote:
Hi Robert et al

It's been a while I use a customized osgVolume::MultipassTechnique and experienced a bug I think was coming from my code but in fact it affect osgvolume application too.
to reproduce
Code:
osgvolume image --multipass --model cessna.osg

It seams there a bug in texgen (or somerhing like that) when writing back Pre rendered scene FB to the main FB..
It lead to artifacts when rotating the view such as
1)models out of volume tend to disappears (experienced in osgvolume ex rotating the view-when cessna comes out of the hull 2D projection-)
2)models duplication (one is deformed and shouldn't be there)



I would like to debug but would like to be sure how it work,
I tend to understand the following, stop me if I'm wrong:
1/VolumeScene children (except tiles) is rendered as in depth and color textures in prerender and copy back to main FBO
2/Tiles Frontface then backface Hull are rendered to determine per pixels ray lengths and then per pixel numiterations ( so rays can be casted in BFHull pass)

It's been a while I haven't dive in there. Can you tellme if I'm wrong and give me directions of what could possibly go wrong in the current MultipassTechnique...

Thank you!

Cheers,
Julien
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robertosfield
OSG Project Lead


Joined: 18 Mar 2009
Posts: 11238

PostPosted: Mon Mar 06, 2017 9:24 am    Post subject:
osgvolume multipass (hybrid geometric/volumic) bug...?
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Hi Julian,

I have just had a bash at recreating issues and have found a volume
model that works in close enough dimensional space to the cessna.osg
that I start seeing problems with the rendering of the volume
occluding the cessna at times when it shouldn't and at certain angles
the parts of the cessna appear in the wrong part of the volume cube.

I haven't seen this issue before so at this stage can't provide any
suggestions as to what might be wrong. I will need to investigate,
but this will need to wait as I'm currently doing a major rewrite of
osgText to resolve issues with how it handles VAO's.

Robert.

On 5 March 2017 at 17:04, Julien Valentin <> wrote:
Quote:
Hi Robert et al

It's been a while I use a customized osgVolume::MultipassTechnique and experienced a bug I think was coming from my code but in fact it affect osgvolume application too.
It seams there a bug in texgen (or somerhing like that) when writing back Pre rendered scene FB to the main FB..
It lead to artifact such as
1)models out of volume tend to disappears (experienced in osgvolume ex)
2)In my own code it cause all sort of strange artifacts

to reproduce

Code:
osgvolume image --multipass --model cessna.osg



I would like to debug but would like to be sure how it work,
I tend to understand the following, stop me if I'm wrong:
1/VolumeScene children (except tiles) is rendered as in depth and color textures
2/Frontface then backface Hull are rendered to determine per pixels ray lengths and then per pixel numiterations ( so rays can be casted in BFHull pass)

It's been a while I haven't dive in there. Can you tellme if I'm wrong and give me directions of what could possibly go wrong in the current MultipassTechnique...

Thank you!

Cheers,
Julien

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