TSC notes for September 27th.

Signed-off-by: jlait <[email protected]>

Author: jmlait

tsc/meetings/2022-09-27.md

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+Minutes from 148th OpenVDB TSC meeting, September 27th, 2022
+
+Attendees: *Jeff* L., *Andre* P, *Nick* A., *Dan* B.,
+*Rich* J., *Ken* M.
+
+Additional Attendees: Karl Marett, Bruce Cherniak (Intel), Michael
+Shenck, Tomas Krivan (SideFX), JT Nelson (Blender), Sebastian Gaida
+
+Regrets: none
+
+Agenda:
+
+1) Confirm quorum
+2) Secretary
+3) Forum
+4) NanoVDB Questions
+5) VDB from Polygons
+6) Scaling SDF in Houdini
+7) MAX FLT from extrapolate.
+8) Move meeting time one hour later
+9) vdb_tool changes
+10) Root Offset PR
+11) Accessor changes
+12) Next meeting
+
+--------------------
+
+1) Confirm quorum
+
+Quorum is present.
+
+2) Secretary
+
+Secretary is Jeff Lait
+
+3) Forum
+
+No issues
+
+4) NanoVDB Questions
+
+Michael has been trying to get NanoVDB to work with GLSL.  Can read
+hard coded offsets but not anything with coordinate index.
+
+This is PNanoVDB.  This is supposed to work.  Ken will put Michael in
+touch with the author.  This might be a GLSL-only issue as GLSL was
+added after HLSL.
+
+Sebastian confirms HLSL still works.
+
+5) VDB from Polygons
+
+Hollow mesh can't convert to SDF because inside gets filled.  We could
+provide an oracle that tells you the sign of the SDF.  Currently done
+as flood fill from outside.  When redistancing you can use the old SDF
+to tell the sign.
+
+Three options:  
+a) If redistancing can just ask the old sdfs value.
+b) Use an oracle like winding numbers, query once each
+tile and flood fill in the tile.  Or, for each voxel, track the sign
+being fixed, and flood fill from there.
+c) We could rasterize signed distance instead?
+
+One mode is to build unsigned and flood from the outside.  Another is
+to trust the surface and use normals.  And the other is to use an
+oracle.  
+
+The current method has some smoothing built into it.  This stops it
+being 1:1, so we will want a mode to disable that.
+
+Can we trust the oracle, or is the flood fill per tile?  What of
+non-determinism with inconsistent oracle?  
+
+Could we post-run a sign check?
+
+We agreed if the provided oracle is inconsistent we can call that
+malformed, and thus be indeterminant.  But if there is anyway to avoid
+that we should.
+
+6) Scaling SDF in Houdini
+
+Should the values scale when you transform the vdb?
+
+If it has the meta data this sounds good, but likely reveals
+inconsistancies in the internal tools.
+
+An option should be added to the sop to transform.
+
+What about negative scale?  Should this invert the SDF?  Negative
+scales should be ignored.  Negative outside is not a valid VDB.  This
+is opposite to how polygons work.  A separate discussion is whether to
+allow negative SDFs to be defined by VDB, but this has a lot of far
+reaching implications.
+
+7) MAX FLT from extrapolate.
+
+Isolated bits of that don't extrapolate are left with MAX that then is
+tracked as the new background.  Should be ignored in sweep and then
+corrected with real background value.
+
+Jeff will send Andre and example file.
+
+8) Move meeting time one hour later
+
+Currently 10am PST, will become 11am.  Likewise 1pm to 2pm for EST.
+(as usual, this tracks daylight savings in North America)
+
+Unanimous vote.  We have to now change the invite.  Ken will try
+and get the time changed.
+
+9) vdb_tool changes
+
+Andre has made many comments, awaiting Ken's comments.
+
+10) Root Offset PR
+
+Original test was simplified.  Everything is working now, but the
+offset modification method isn't as fast as it used to be.  Had
+forgotten about inactive tiles.  After a final benchmark it will be
+submitted.
+
+Original PR is just to have the offset.  Modifying the offset is a
+method on the tree.  Should it be a dynamic node manager?
+
+Ken will make the PR public after this call.
+
+11) Accessor changes
+
+PR 1452 - improvement for accessors.
+
+Ken also has an accessor improvement for caching tiles.
+
+12) Next meeting
+
+Next meeting is on October 4th, 2022. 2pm-3pm EDT (GMT-4).
+
+NOTE: This is one hour later.