[Sidefx-houdini-list] Fast character cloth sims

Vincent Fortin vfortin at gmail.com
Wed May 31 10:26:13 EDT 2017

Also FEM is highly dependent on scene scale. Check your units and try
scaling down your model. Rebuild your setup from scratch and compare
simulation times.

I'm not a cloth expert either but this has helped me a lot in the past. I'd
be curious to have a look at your scene if you can share it.

Good luck!

On Wed, May 31, 2017 at 7:08 AM, Phil Spicer <PSpicer at bournemouth.ac.uk>

> 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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