[Bf-committers] It's time to get rid of cloth

[darkdefende at gmail.com]

To fix the cloth tunneling though the cube, activate "Single sided" in
the cube's collision settings and it should work much better.

Anyways, during my recent work with Bullet, I tested some things that
are currently not integrated into blender.

Mainly Bullet softbodies and cloth.

Both have their use cases, but as Brecht pointed out, the Bullet cloth
physics is way more unstable and doesn't have no where near as many
features as our current cloth sim. So outright replacing our current
system with that would just be a downgrade on so many levels (except
speed).

I would say that all of our physics simulations currently needs a lot of
work to be faster, more stable, and nicer to use. The majority of them
feels half baked at the moment I my opinion. (And it shows as it seems a
lot of people does not use them in production because they are simply not
good enough yet)

My current plan was to first make Bullet integration in Blender better.
As I deem this to be the easier task. However I have a lot of other work
I need to do, so progress is slow.
This is also because I want the Bullet refactor to align nicely with our
new node system. (So we don't have to do an other refactor for that)

As Sergej pointed out, Mano Wii and I has been in talks on making the
collision system better for cloth and also make it have move options so
they user can make trade-offs if they want to.

If you have any specific fixes or changes in mind. We would love to hear
them.

Welcome back.

On Tue, Oct 20, 2020 at 01:39:01PM +0200, Sergej Reich via Bf-committers wrote:
> Bullet's cloth system is no replacement for what Blender currently has and
> I'm not aware of any available library that we could use without having to
> do a lot of modifications to make it work.
> 
> Am Di., 20. Okt. 2020 um 12:26 Uhr schrieb Brecht Van Lommel via
> Bf-committers <bf-committers at blender.org>:
> 
> > The most important thing for cloth is that you can get it to give good
> > results in real world cases, and the cloth simulation changes were based on
> > work done for Agent 327.
> > https://www.youtube.com/watch?v=jU6-cI-z8HA
> >
> > In practice you use smaller time steps and the fast-moving cube will get
> > collided with anyway.
> >
> > Continuous collision detection is great for handling fast-moving objects,
> > but arguably handling cloth that is nearly at rest and continuously
> > colliding with the character is a much harder problem. Most cloth
> > simulation demo videos stop while everything is still in motion, but what
> > happens after is just as important.
> >
> > Anyway, there's definitely much room for improvement here, but it should be
> > tested on real-world cases. For example from what I've seen, Bullet cloth
> > is more reliable at high frame rates, but does not produce good results or
> > wrinkling details when turning up the quality. I've not yet seen an
> > open-source cloth library that we could just plug in and get much better
> > results, but it would be great if there was one.
> >
> > Some work on cloth collision is being done here:
> > https://developer.blender.org/D8577
> >
> > On Tue, Oct 20, 2020 at 11:52 AM Ton Roosendaal via Bf-committers <
> > bf-committers at blender.org> wrote:
> >
> > > Hi Joe,
> > >
> > > This is a bit harsh, there have been good cloth contributions to Blender
> > > by Luca Rood. The current module owner for it is Sebastian Parborg
> > though.
> > >
> > > I'd suggest to connect with them to see what steps forward could be.
> > >
> > > We are also in the process of making a good node physics system to allow
> > > solvers like this in a more generic setting. Design for this is ongoing.
> > >
> > > It's super cool to see you want to come back, just give it a bit of time
> > > to figure out who's doing what now.
> > >
> > > Als note that we (including Blender Foundation / Institute) are in the
> > > process of organizing ourselves much better, including onboarding, best
> > > practices, engineering standards amd strict requirements for a good
> > > design process - including the docs.
> > >
> > > We lack in a lot of areas, and the consensus is to especially put
> > > efforts in bringing the current state of the code in control (functional
> > > and technical specs), before recoding modules entirely.
> > >
> > > -Ton-
> > > ----------------------------------------------------------------------
> > > Ton Roosendaal - ton at blender.org - www.blender.org
> > > Chairman Blender Foundation, Director Blender Institute
> > > Buikslotermeerplein 161, 1025 ET Amsterdam, the Netherlands
> > >
> > >
> > > On 20/10/2020 00:30, Joe Eagar via Bf-committers wrote:
> > > > So, ten years ago I wrote several continuous collision detection
> > systems
> > > > for cloth/hair, one of which I tried to push into trunk:
> > > >
> > > > https://www.youtube.com/watch?v=QBM3TBKO9w8
> > > >
> > > > And, here's how the cloth sim performs today:
> > > >
> > > > https://www.youtube.com/watch?v=5462m9yEkU8&feature=youtu.be
> > > >
> > > > If the cloth development process is this dysfunctional (this patch
> > > actually
> > > > passed review?
> > > >
> > https://developer.blender.org/rB0666ece2e2f96571200d693d9d7bee1ca72d026f
> > > )
> > > > then I propose we eliminate the cloth code entirely and go with a third
> > > > party lib (Bullet?).
> > > >
> > > > Joe
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