add next hit HDDA to PNanoVDB

[gaida-exe]

Signed-off-by: Sebastian Gaida [email protected]

[gaida-exe]

This PR adds a new variant of the HDDA algorithm to PNanoVDB.
Before, there was only a zero crossing function, and this would add a variant that gets the next hit above 0.
Reason: The background value is often 0 and therefore the other HDDA zero crossing would never report a hit, because it checks for a sign change from start of the ray to tested voxel.

[gaida-exe]

Hello @kmuseth I checked NanoVDB and if there is a function that matches the current proposed function and there is.
The TreeMatcher, like the proposed function, also marches with the HDDA to find the first active value and return true as well as the coordinates ijk. The difference is that the PNanoVDB function only returns if the value is greater than a given minimal value.
This is essentially the same check that you are doing in NanoVDB for the Generic Grids(this is a link)
In PNanoVDB we can't check for nullptr, but we can check for a value greater than 0 and also add the functionality to check for a value greater than the desired (link).

[kmuseth]

That probably only needs to be PNANOVDB_IN(float) minimalValue

[kmuseth]

@gaida-exe I have two issues with the current version of the HDDA:

• It is is different from the one in NanoVDB.h which is problematic because it obviously means that their behaviors and APIs are now out of sync
• I don't fundamentally understand why a tolerance is desirable. The background value for fog volumes should always be exactly zero

[gaida-exe]

Hello Ken, I agree with you and I removed the minimalValue. I also renamed the function to be the same of NanoVDB.

[danrbailey]

Hi @gaida-exe, can you push an empty commit to this MR to trigger the CI to run again? Seems like it got stuck on one of the builds so we cannot merge in it's current state, thanks.

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[linux-foundation-easycla]

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[gaida-exe]

Sorry for the CLA noise.