[Soc-2018-dev] Weekly Report #9 - Further Development for Cycles' Volume Rendering

[Geraldine Chua]

​Sorry for the late report everyone, as I was hoping to be able to finish
up the node code before this weekend was over.

This week, I worked on the following tasks:

   - General code clean up and bug fixing with both sparse tiles and
   OpenVDB.
   - Edit Cycles stand-alone build files to support OpenVDB.
   - Move import interface into a dedicated Cycles node.

In order to have a more solid integration of OpenVDB importing in Cycles,
it would be better to not need to rely on Blender's Smoke Domain Settings.
Cycles is a heavily node-based program, so I think creating a node for
OpenVDB import would work well with the current architecture. The current
state of the node:


​
(Fields are filepath, grid, interpolation, and extension. Output is color,
vector, and fac)

The idea behind the OpenVDB Import node is that it will function similar to
the Attribute node, where it will add an image using the vdb file and grid
name provided (saved as a texture), and if the grid name is a valid
attribute, it will also add the attribute to the object. This in theory
means it can substitute for a voxel attribute node. The object will then be
treated as the domain / bounding box of the vdb texture.

The node structure is still tentative, as there may be better ways of
implementing it since I am not entirely familiar with the node
architecture. Some simple alternatives:

   - Base it on the Principled Volume Node instead of Attribute, which will
   allow being able to load all grids in one node instead of having one node
   per grid per file. This will require forcing specific grid names, which may
   be too inflexible.
   - Accept an Attribute Node as an input instead of having a grid field
   (not too important of a distinction I think).

Regardless of implementation details, the image slot number and the
attribute must be passed along to the object.

*To-dos next week*

   - Finish node implementation.
   - Try to connect the current VDB previewer to the new node.
   - Finish testing Cycles stand-alone.
   - Figure out the strange memory measurement issue with OpenVDB grids.

Hopefully, all of these could be done before the end of the week, in which
case I will move on to my next task.

*Questions*

What possible improvements / changes should be done with the node?
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