Blender grid rendering interprets voxel transforms in such a way that the voxel
values are located at the center of a voxel. This is inconsistent with OpenVDB
where the values are located at the lower corners for the purpose or sampling
and related algorithms.
While it is possible to offset grids when communicating with the OpenVDB
library, this is also error-prone and does not add any major advantage.
Every time a grid is passed to OpenVDB we currently have to take care to
transform by half a voxel to ensure correct sampling weights are used that match
the density displayed by the viewport rendering.
This patch changes volume grid generation, conversion, and rendering code so
that grid transforms match the corner-located values in OpenVDB.
- The volume primitive cube node aligns the grid transform with the location of
the first value, which is now also the same as min/max bounds input of the
node.
- Mesh<->Grid conversion does no longer require offsetting grid transform and
mesh vertices respectively by 0.5 voxels.
- Texture space for viewport rendering is offset by half a voxel, so that it
covers the same area as before and voxel centers remain at the same texture
space locations.
Co-authored-by: Brecht Van Lommel <brecht@blender.org>
Pull Request: https://projects.blender.org/blender/blender/pulls/138449
12f0bc7736