VDB SDF Blending

[kshay]

Hi All!

 

I have been trying to create a smoothly blended intersection between two pieces of animated geometry by using VDB SDF's.  The end goal is to have highly detailed geometry with blended intersection points that have a few controls to adjust how the blend looks.  

 

I was pointed towards the paper on Spiderman 3's Sandman showing the mathematics used on the levelsets, and then found GallenWolf's post referencing the paper and showing how to achieve the look within vops with isooffset volumes:

  http://forums.odforce.net/topic/17978-sdf-blending/

 

These were both extremely helpful, thank you!

 

However, creating this setup with VDB's is alluding me!  I don't quite understand how the math is working to blend the levelsets the way it is, so it is proving difficult to adjust anything that might be needed within the Volume Vop.  I have also been able to isolate the intersection area with a vdbactivate, but I am fumbling a bit trying to figure out either the next step or if that is even a necessary step.

 

When plugging the vdb's directly into the math from the original isooffset setup, I get a negative valued band where the intersection is happening, so something is working.  The second VDB is completely lost at this point though.  On top of that, the original parameters designed to adjust the radius of effect and such are not behaving in any understandable way for me.  They seem to be adjusting something?

 

I have attached a cleaned up version of the hip file I am testing with.  Any knowledge anyone has on the subject would be greatly appreciated!  I'm pretty sure I'm going in circles.

 

Thank you,

  

vdb_blend_v001.hip

[goldleaf]

For combining a couple of VDBs, VDB Combine works well, especially in this case. See the hipfile/screenshot.

 

 

You don't have to have the same name between the vdbs, but I like to do that for organization (if I'm intending to simply combine them).

 

Does that help?

vdb_blend_vdbcombine.hip

[kshay]

Hi Chris,

 

Thank you for your response!

 

Combining the vdb's could be a first step I'll need to take.  The problem after that is creating a smooth blend at the intersection points that I have control over.  

 

As an update, I did find that if I increased the number of Exterior Band Voxels when the vdb's were originally created, it would complete the blend and give me similar results to using isooffset volumes.  However, it's ridiculously slow and inefficient which is what I was trying to get away from in the first place haha.  But it did mean that the math was working correctly I suppose.  I worked on it a bit more and tried activating just the areas of each of the vdb's that I would need, but it's still not wanting to successfully create the blend with what seems like all of the vdb voxels included in the vopsop calculations  Does anyone know if I'm using vdbactivate correctly?  Maybe I need to create a third vdb with a certain value in the voxels to give the blending algorithm something to calculate with since I'm trying to limit the calculations to be done only in the area they need to be?  You can see in the file I'm attaching here how it wants to blend, but it glitches out.  

 

Thanks in advance for the time anyone takes in helping me!

 

 

vdb_blend_v002.hip

Edited May 5, 2014 by kshay