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Packed Prims and UVs

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Guest tar

Nice, getting there. - Houdini also does caching and frustum culling. 


Dollyed into the still fish abc scene is 15fps, zoomed out is 8 fps

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Now i getting the fishes work. it is now 8 pack à 800 fishes. And its must be for 360° projection with an resolution of 8k :(

i think the birds are more challenging becaues these are 30k. but i will clustered in different abc packages.

At the end I really love abc regarding size but I also hate it


..and thanks all and esp. marty for taking so much effort and time for helping!!! great forum.

Edited by tfreitag

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hehe...last question regarding mblur with alembic/packedprims:


whats the best for vector mblur inside alembic. I have to compute the vel. Is it enough to pass v of template points in copysop? and is alembic rop automatically looking for v-attrito to write it in the  alembic arbGeo.v channel?


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The support tooks a look inside my hipfile, with allso very great and helpfull information about abc format. So that everyone could benefit I will post it here:



The issue is the Alembic output node is getting confused when trying to match the packed primitives from frame to frame. So, it's creating new geometry on some frames (since it thinks the topology is changing).

I was able to work around this issue by:
   - Add a new stamp parameter, I called mine "number" and set its value to $PT (the point being copied to).
   - Insert a pack SOP before the copy to manually pack. Setting the path attribute to << op:`opfullpath('.')+stamp("../

copy1", "number", 0)` >>
   - Turn off Pack Geometry in the copy SOP
   - In the Alembic ROP, turn on partitioning geometry by attribute
   - Set the attribute name in the Alembic ROP to "path"
This helps the Alembic ROP match primitives since the path attribute matches.

Without this change, when I saved the Alembic, I was getting 5000+ shape nodes in the .abc file (over 20 frames) when there were were only 1685 points. After the above change, there are 1685 Alembic primitives when I load it in.

When I read in the Alembic, the geometry also matches.

We'll try to figure out why the Alembic ROP isn't able to match geometry properly though.

Also, with your current set up, you may not be getting ideal instancing in Alembic.

For instancing to work, you'll need to have the same shape duplicated multiple times. Since you're doing blending of the copied geometry, your likely getting duplicated geometry.

In addition, with stamping, you're unlikely to get shared geometry between copies unless you turn on "Cache Stamping Geometry" - which will compute all the different stamping possibilities and create "shared" versions of the geometry for stamping. Of course, since you're using floating point parameters for stamping, you're likely not going to get duplicate geometry there either. Even if you were able to have shared geometry, the instancing in Alembic works across all frames, so it's quite possible that if the geometry is shared, then unshared, this would cause big hiccups in Alembic export (a shared instance needs to be shared over all frames)."
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Hey guys, adding to this coversation,. 

I require help dealing with packed alembic within houdini 17.5/18.

I have a heavy geo but im getting an issue with textures not showing properly unless unpacking but unpacking causes scene to be extremely heavy. 


So is it possible to keep it a delayed packed primitive and unpack only the uv attribute to maintain the scene being lighter and yet allows the unpack uv to be read within renderman for houdini. 


Any thoughts? 

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