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no motion blur with autosmooth - cycles
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Description

System Information
WIndows 7 / geforce 780ti

Blender Version

2.72a 73f5a41

Exact steps for others to reproduce the error
No motion blur on deformable mesh (armature modifier) when autosmooth is on, rendering with cycle. When autosmooth is Off, all is fine.

Based on a (as simple as possible) attached .blend file with minimum amount of steps

Event Timeline

Olivier Pautot (pixl) raised the priority of this task from to 90.
Olivier Pautot (pixl) updated the task description. (Show Details)
Olivier Pautot (pixl) edited a custom field.

you can test with this link :

wing.blend

Bastien Montagne (mont29) lowered the priority of this task from 90 to Normal.
Sergey Sharybin (sergey) changed the task status from Unknown Status to Unknown Status.Oct 21 2014, 4:51 PM

The thing here is Cycles splits the triangles which crosses the autosplit angle threshold. This could easily lead to topology changes which would make motion blur work incorrect.

Proper solution is to not do geometry split but store decoupled normals,making the render kernel aware of this. This would be handled as a general Cycles improvement TODO. I've linked this report from there http://wiki.blender.org/index.php/Dev:2.6/Source/Render/Cycles/ToDo

Thanks for the report, but i'd consider this a TODO.

By using a edge split I can have the same result and the motion blur works!
Thank you!