Tearing nCloth, No Motion Blur!

#1

Hi, i having some difficulty rendering motion blur on tearing nCloth mesh.
Im rendering with Arnold, and originally posted this in the rendering sub-forum but after further reading about this, its actually an nCloth issue.

From what i gather, MB cant be calculated because the mesh is changing topology and adding new edges etc.

Ive done a lot of searching and found a post by Howard where he said to make a geometry cache from the nCloth, which will calculate MB correctly, however im having some difficulty creating this cache.

When i create it, the mesh goes crazy and overlaps and becomes a mess. Im unsure of the correct method to create a geometry cache so far i have tried:

Creating it from the nCache, Creating it direct from simulation, Creating it from an Alembic cache of the nCache. They all seem to act strangley. Or should i be chooseing ‘Export Cache’? I can post an example scene to deomonstrate if its not clear whats happening from this.

After further reading i found a post in which Duncan said to do nCache>Transfer Cache to Input Mesh, which behaves the same as a geometry cache. However this dosn’t seem to work either, and get no animation in the mesh at all after doing this, and if i could get it to work, i still dont know if it would calculate MB.

Running out of ideas, and would really appreciate any suggestions anyone has. How can i get my tearing nCloth to be motion blurred?

Cheers

#2

Perhaps the Soup plugin can do it?

http://www.soup-dev.com/examples2_3.htm

Look at the bottom of the page.

#3

Hi, thanks for the reply, yeah currently looking in to using soup and having some success. It seems a common problem with MB on meshes with changing topology.
I just thought i would ask here as others have said a geometry cache will calc MB fine without having to create motion vector data for the mesh before hand.

#4

What difficulties are you having making a Geo Cache?

#5

Hey Howard, just the man. It appears to run through fine but when rewinding, the mesh just gibs out, cant explain why.

Also unsure of the proper workflow for creating a geo cache, how can i create one from an nCache? i just get the message to replace or blend caches.

Try creating a geo cache on this scene and see if it happens to you, its really weird.
nClothTear_01.zip (2013 .mb)

Ended up venturing over to Soup because i couldnt get this to work, but would definitley like to know why.

#6

Its the merge on the ncloth, you need to cache it without and then add it to the geocache.

#7

Ah i see, i did as you said and it works fine, thanks. However the geometry cache dosn’t seem to allow MR to calculate motion blur :confused: Managed to sort it with Soup though.
At least i know now that the merge is no good for geo caches.
Cheers

#8

I was looking into this some more and you were right, the geo cache does indeed calc motion blur correctly.

However im having a weird rendring issue, tried with both Arnold and MR, when batch rendering the cloth moves as it should, but no tears actually happen.

I did as you said and disconnected the mergeVert and polySmooth nodes before geo caching, but the batch render just wont show tear lines despite single frame renders working. Do you have any ideas?

Cheers

#9

Sorry not sure what is up with that. You sure your mesh is prebroken? You sure it renders single frames with tears from the same geo?

This may help with Motion Blur - https://support.solidangle.com/display/AFMUG/Motion+Vector+Source

#10

Yeah 100% sure.
Ive tried removing some of the nodes and its the polyMergeVerts thats responsible. When removing this the tears happen in the batch render, but it renders with sharp polys.

Im adding this back in to the chain after creating GeoCache, from the geoCache to the outMesh, with the polySmoothEdge inbetween too, these appear to soften the mesh, otherwise its like the normals arnt soft. I can try to post some pictures to explain but cant post a scene because it wont have the Geo cache.

The polySmoothEdge dosnt seem to do anything without the MergeVerts either :confused:
Really confused by this.

Yeah I was using Arnold motion vector source, and piping through from Soup, which works if i go direct from the Soup node to the mesh, but incidentally as soon as i re-add the polyMergeVerts and the PolySmoothEdge nodes in between, Arnold wont render the motion blur correctly.

Is there any chance you could do a quick geoCache of the example scene i posted, re-add those 2 nodes and batch render a couple frames just to confirm its not just me going mad.

Without those 2 nodes it all renders fine and with MB, but obviously the mesh is not smoothed. This is the case with both Arnold and MR.