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alembic results in hair with "random position per frame" in render time
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Description

System Information
Operating system: windows 10
Graphics card:GTX 1080

Blender Version
Broken: 2.80, 2019-01-26, 25772c9e1d2d, branch: blender2.7
(example: 2.79b release)
(example: 2.80, edbf15d3c044, blender2.8, 2018-11-28, as found on the splash screen)
Worked: (optional)

Short description of error


When using rendering hair and using alembic as mesh cache (Mesh Sequence Cache modifier) I get unique root positions of each hair strand per frame. This bug can only be seen in rendertime. When looking at the fur in the viewport, everything looks fine.

When using MDD as cache format, this issue can not be seen. Only alembic cache seems to be affected.

Exact steps for others to reproduce the error
Based on the default startup or an attached .blend file (as simple as possible).

  1. create a sphere

2 add a displacment modifier with cloud texture and animate the displacement. Any deform modifier will do

  1. Export the sphere as alembic
  2. Duplicate the sphere
  3. add a Mesh Sequence Cache modifier and connect it to the exported alembic.
  4. add fur. Use few hairs so it's easier to spot the random hair poisition per frame.
  5. scrub the timeline. Notice that the hair looks fine in the viewport
  6. render the image sequence. Look at the rendered images and see that the fur looks really noisy/jittery per frame

Details

Type
Bug

Event Timeline

Daniel Bystedt (dbystedt) renamed this task from alembic results in hair with "random seed per frame" in render time to alembic results in hair with "random position per frame" in render time.
Sebastian Parborg (zeddb) triaged this task as Confirmed, Medium priority.

Just a quick note, I had to change search path for the abc file as it had an absolute filepath with the mdd had a relative one and worked out of the box