Vertex parent was using original non-modified nurbs list, simply because
it didn't have something else to operate with.
Now we've got deformed by pre-tessellation modifiers nurbs in the curve
cache which might be used y the vertex parent.
Root of the issue goes to the fact that bevel list calculation might drop some points
if they're at the same position. This made spline length calculation goes wrong.
Now the length of the bevel segments is stored in the bevel list, so values are
always reliable.
Initial patch by Lukas Treyer with some tweaks from me.
Bevel Factor Mapping allows to control the relation between bevel factors
(number between 0 and 1) and the rendered start and end point of a beveled
spline.
There are three options: "Resolution", "Segments", "Spline". "Resolution"
option maps bevel factors as it was done < 2.71, "Spline" and "Segments"
are new.
* "Resolution“: Map the bevel factor to the number of subdivisions of a
spline (U resolution).
* "Segments“: Map the bevel factor to the length of a segment and to the
number of subdivisions of a segment.
* "Spline": Map the bevel factor to the length of a spline.
Reviewers: yakca, sergey, campbellbarton
CC: sanne
Differential Revision: https://developer.blender.org/D294
Issue was caused by curve orco calculation for rendering being freed
curve path and not calculating it back.
This left depsgraph in a state that it believed all the object data
is up to date but in fact some parts of data was freed by convert
blender.
Now made it so path is not being freed by render thread. This is
rather a workaround actually because ideally render thread need
to use copy-on-write here or at least use local cache here. But
current logic should be closer to what was happening in previous
release.
