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meeotch

vdb from particles error

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I've got a flip fluid that I'm surfacing using the Particle Fluid Surface node, and I had one frame that produced geometry but wouldn't render.  Turning off geometry motion blur for the render geometry allowed it to render, but somehow screwed up my shader so that the result was all white.

 

Anyway, long story short, I traced it back to a small hole that was appearing in the surface on that frame.  And then I traced that hole back to the VDB Dilate inside the Filter subnet inside the Particle Fluid Surface node.  After much weeping and gnashing of teeth, I narrowed it down to 14 points in my fluid.

 

See the attached file.  If you view the VDB Dilate node, you'll see a missing chunk in the vdb.  If you check out the geometry of the Convert VDB node, you'll see NaN's.

 

Deleting any one of the points (blast node) fixes it.  Jittering by even a tiny, invisible amount (jitter node) fixes it.  The points only have P and pscale attributes, and none of the values seem to be weird, as far as I can tell.

 

Bug?

 

Bonus question:  I often find that the Particle Fluid Surface node will output no geometry when I view it, and I'll have to allow editing then dive in and view individual nodes in order to "wake it up".  Generally, it's the final VDB smooth that seems to be asleep.  (I've noticed this as well when rolling my own surface with VDBFromParticles-->VDBReshape-->VDBSmooth-->VDBReshape in old versions of Houdini.)  I don't think this is a problem when rendering out the geo, though.  Has anyone else encountered this, or more importantly, have a workaround for poking the Particle Fluid Surface node & forcing it to recook without having to dig around in its guts?

brokenvdb.hip

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See the attached file.  If you view the VDB Dilate node, you'll see a missing chunk in the vdb.  If you check out the geometry of the Convert VDB node, you'll see NaN's.

 

Deleting any one of the points (blast node) fixes it.  Jittering by even a tiny, invisible amount (jitter node) fixes it.  The points only have P and pscale attributes, and none of the values seem to be weird, as far as I can tell.

 

Bug?

 

 

Most likely in the Resample Input option on VDB From ParticleFluidSurface.  The issue also goes away if use a higher Renorm Accuracy on the Dilate node, which maybe should be an option on the ParticleFluidSurface node, or possibly we should just default to it internally.  Would you mind submitting a bug?

 

 

Bonus question:  I often find that the Particle Fluid Surface node will output no geometry when I view it, and I'll have to allow editing then dive in and view individual nodes in order to "wake it up".  Generally, it's the final VDB smooth that seems to be asleep.  (I've noticed this as well when rolling my own surface with VDBFromParticles-->VDBReshape-->VDBSmooth-->VDBReshape in old versions of Houdini.)  I don't think this is a problem when rendering out the geo, though.  Has anyone else encountered this, or more importantly, have a workaround for poking the Particle Fluid Surface node & forcing it to recook without having to dig around in its guts?

 

 

This issue has been fixed recently:

icon_vdb.jpgWednesday, February 3, 2016 

Houdini 15.0.376: Fix refresh problems when interrupting the cooking of various VDB filtering nodes. This also fixes the refresh problems of the Particle Fluid Surface SOP, which internally used these VDB nodes.

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Submitted - thanks.

 

And good to know that the refresh thing has already been squashed.  You guys rock.

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Support is reporting that the vdb "holes" thing is fixed in VDB 3.1 & we'll see it in Houdini 16, so I guess the problem was further down the rabbit hole.  In the meantime, it's good to know that changing Renormalization is a workaround.

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