Imported curves lag behind one frame.
Open, ConfirmedPublic

Description

System Information
Linux Mint 17.3
I5 3550 - 32gb RAM , Asus Geforce 750Ti OC

Blender Version
Broken: release candiate 2.78

Short description of error

Tested the import export from Houdini to Blender via Alembic abc format. There is a problem with curve objects.

Exact steps for others to reproduce the error

I tried to export Fur from Houdini to Blender via Alembic. When i exported it everything works fine. Blender converted this polylines or even Nurbs Curves to Blender Nurbs Curves. So far so good. But. When you play the animation sequence the curve Objects in Blender (fur Curves) lagging a Frame . Means. You need to push one frame forward to get the Curves in the correct possition then you need to step one frame back to get the geometry back to where it has to be. The curves dosent move. .. In Short Words there is a Frame Redraw Lag or Reading lag for Curves.

My Solution was to convert all Lines in Houdini to Polyllines then i extruded them to get a real Polygone. I exported the polygone Hairs again -> everything works fine with real geometry. Hope this gets fixed soon.

For still import (no Sequence the import of Alembic even with Nurbs curves works perfectly)

BIG THANKS TO ALL THE INVOLVED DEVELOPERS FOR the ABC INTEGRATION!!!!!

Cheers

Alex

Details

Type
Bug
Kévin Dietrich (kevindietrich) triaged this task as "Incomplete" priority.Sep 25 2016, 3:11 PM

Thanks for the report but we would need a simple Alembic archive that demonstrates the issue.

This File provides the Houdini Export File, the ABC File and the Import Blender file. Its the same problem with Nurbs curves. Hope that helps

Ps When you play the animation foward step by step you see the lagging of the curves.

Kévin Dietrich (kevindietrich) raised the priority of this task from "Incomplete" to "Confirmed".Sep 25 2016, 4:34 PM

Thanks for the files, can confirm the issue.

First of all very nice with Blender 2 78b it works nice. But is it possible to store point color dats on those curves? I think thats not possible but is it possible to import alembic files of point clouds with stored color data what alembic is exporting in houdini. Its stored but blender dosent import it..

If this is not possible it would be nice when blender can import polylines with stored vertex color information right now every curve even polycurves from houdini are Imported as bezier/nurbs Curves.
Maybe a import option could help

Best regards Alexander Weide..

Vertex colors are a mesh property in Blender, so it is not possible to import/have them on curves at the moment. Making use of polylines (or edges in Blender terms) would be possible, but then things like rendering in Cycles might not be possible or very limited. The fact that Houdini polylines/polycurves are imported as curves in Blender is because they are written as being curve objects in the Alembic archives.

Sybren A. Stüvel (sybren) changed the title from "Release Candidate 2.78 Alembic Bug with Polylines or Nurbs Curves" to "Imported curves lag behind one frame.".Thu, Apr 20, 12:05 PM

This issue (lagging of imported curves) is a known problem, which is caused by limitations of the current modifier system in combination with Alembic. The modifiers are made to either construct a new object or deform an existing object. Since Alembic curves can change topology from one frame to another, the Mesh Cache modifier needs to do both (i.e. create a new object when the curve topology changes, and deform an existing object when it doesn't). To fix this properly, we'll have to modify the modifier system to allow both. I don't know if I can do this (or work around this issue another way) in time for 2.79; if not, we'll work it out in 2.8 (in which case there will be a different, more elegant approach to handling cached data).

But is it possible to store point color dats on those curves?

Please stay on the topic of the ticket, and open a new ticket for a new topic.