Merge pull request #1778 from sideeffects/sendupstream_tsc20240319

Meeting notes of March 19th.

tsc/meetings/2024-03-19.md

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+Minutes from OpenVDB TSC meeting, March 19th, 2024
+
+Attendees: *Jeff* L., *Andre* P, *Dan* B., *Greg* H., *Rich* J.
+
+Additional Attendees: 
+Dhruv Govil, Ivo Kondapaneni
+
+Regrets: *Ken* M., *Nick* A.
+
+Agenda:
+
+1) Confirm quorum
+2) Secretary
+3) OpenVDB Half Grids
+4) Load as Half Patch
+5) Next meeting
+
+------------
+
+1) Confirm quorum
+
+Quorum is present.
+
+2) Secretary
+
+Secretary is Jeff Lait.
+
+3) OpenVDB Half Grids
+
+Support for half without a compute type is much slower and has
+significant errors.  Proposal is to add a Tree::ComputeType that is
+identity with ValueType, but float for Half.
+
+For many tools, like stencils or volumes, should they return Compute
+Type?  Does this break ABI?  It shouldn't as the typedef should decay
+to the base type for mangling?  We could use an enable if to work
+around if it somehow does mess up ABI.
+
+What should be compute types?  
+
+Stencils have a value type that is there value type, different from
+the tree's value type, so they can logically set this to the tree's
+ComputeType.
+
+How to get accessors or setters to use ComputeType?  We could have
+getComputeValue or getValue for the two types.   But widening is free?
+
+Should I be able to make stencils any compute type?  With the tree's
+compute type just the default?  Eventually do we want float grids with
+a compute type of double?  Probably yes, but beyond this PR.
+
+Import and export doesn't conflict with save float as half - they are
+independent and this flag is ignored with half.
+
+What half type do we use? All of our half types are the same
+underlying bit pattern so it doesn't matter.
+
+4) Arnold support for Half
+
+How to load a float grid as a half grid.  Add a scalarConversion type
+for what the new grid's type should be.  
+
+We set that to the stream's metadata, and the grid descriptor uses
+that.  This creates a CreatingReaderFactory to read the source and
+write out as the desired type.  
+
+Raw is.read() with reinterpret are replaced by the converting reader
+that might do some casting internally.
+
+seek should be seekElement() and take the count and position to make
+it clear what it is doing.
+
+Delayed loading will work as the stream has the converter attached to
+it.
+
+Will be made as a PR for further discussion.
+
+5) Next meeting
+
+Next meeting is on March 26th, 2024. 2pm-3pm EDT (GMT-4)