[Sidefx-houdini-list] Fast character cloth sims

Phil Spicer PSpicer at bournemouth.ac.uk
Wed May 31 07:08:20 EDT 2017


Hi Steven,

I have always found cloth to be fine in Houdini and I also remember a cloth competition a few years back where a wide variety of costumes and material types were developed by Houdini Artists, so great cloth can definitely be achieved.

I am no cloth expert by any means, but the key workflow considerations I’ve found to reduce simulation times are:

1. Use a Soft Peak or Peak SOP to slightly inflate your character collision mesh. This inflated mesh is hidden at render time with the original character mesh being used instead.
2. Activate Concave Bullet Collision geometry for the inflated collision mesh.
3. Ensure your cloth geometry is triangulated (for example using a Divide SOP)
4. Have less topology on your cloth geometry, and subdivide it post simulation to create the final cloth aesthetic.
5. Use the Rest Geometry / Target Geometry options to help give more bespoke movement and shape to the cloth (for example animated rippling rest geometry).
6. Set the Cloth Thickness appropriately, and check its thickness by activating the cloth thickness guide.
7. Surface Mass Density can be set quite low (for example 0.005)
8. Normal Drag and Tangent Drag can be set to 0.
9. Material Stiffness can initially be set to 1.
10. FEM Solver Minimum Substeps can be channel referenced into Max Collision Passes, Penetration Recovery and Max Fully Implicit Passes, so they can be increased simultaneously whilst still keeping their values relatively low.

I would do a basic setup such as this before playing with the more bespoke cloth physical parameters such as the ones you mention.

I have a simple cape skirt example file I can send you if you want based on the above, and the visual result is a slightly heavy cloth aesthetic with a fast sim. I can be emailed directly at pspicer at bournemouth.ac.uk<mailto:pspicer at bournemouth.ac.uk>

Kind regards,

Phil.



Philip Spicer
Programme Leader - MA Digital Effects
National Centre for Computer Animation
Bournemouth University - UK

https://www.youtube.com/user/NCCADigitalFX


On 31 May 2017, at 00:12, Steven Quinones Colon <steven at stevenquinones.com<mailto:steven at stevenquinones.com>> wrote:

Hi Guys,

A very simple nooby question. I have a simulation of a character being thrown across the room. He is an alembic animation about 18,000 points as a collider, and  has a business suit(just a jacket now for testing) with about 42,000 points, and I'm getting really flimsy looking cloth(more like silk) with the soft leather preset,  it's also taking more that half an hour per frame for the simulation. I've played with Stiffness Multiplier and Stretch Stiffness but anything past 2000 slows everything to a crawl, dampening helped. Any tricks from the experienced folks for this kind of sim for both of these problems?

Best,

Steven

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