Physics Obi Particle Based Physics (Cloth, Rope, Fluid) thread

Hi there,

Please write to our support email (support(at)virtualmethodstudio.com) or forums. Thanks!

 

Hi!
I'm using the 6.2 version and testing out surface collisions. First of all, do I understand it right, that even with surface collisions enabled, I still have to add a native unity collider component + obi collider component to the object that I want my cloth to collide with?

And more importantly, why, if I move the cloth and bash it against an object, it collides well even at high speed, but when I do the opposite (move the object against the cloth) it goes through the cloth even at very low movement speed and causes big stutters and fps drops?

 

Yes, surface collisions simply extend the collidable surface of cloth/ropes from individual particles to the whole surface. You still need colliders for it to collide against. See:
http://obi.virtualmethodstudio.com/manual/6.2/surfacecollisions.html

It shouldn't. There's no difference whatsoever in moving the cloth against a collider or a collider against the cloth. Please write to our support email/forums and provide some more info (a video of the issue, details about your setup) so that I can offer proper help.

 

Thanks!
I've sent video to support@virtualmethodstudio.com

Btw, the same behaviour can be observed in your example scene "ClothStaticMeshCollider". If you drag a cloth around the scene it will collide with the body mesh, but if you will move the body mesh it will almost always go through the clothes.

 

Oh ok, I see what you mean. This is just plain old tunneling:

The mesh in that particular sample scene is a MeshCollider, and MeshColliders are hollow by definition (since they are just a collection of individual triangles, they do not define a “volume”). This means that once a object gets "inside" the mesh, it cannot be projected outside since the engine does not know what's inside or outside of a MeshCollider. It just knows about its surface. Since triangles are infinitely thin and particles very small and fast, this problem is exacerbated.

Not only that, but you’re probably moving the mesh around by setting its transform position directly (using Unity’s gizmos). This basically teleports the mesh around from frame to frame, ignoring CCD checks. Since the engine cannot predict where you're going to move the transform next, it cannot perform accurate collision detection along the way.

The reason why moving the cloth against the collider works, is because particles in the cloth move as a result of a physics simulation (unlike setting the transform of a collider), they have a velocity, and CCD (continuous collision detection) is used.

Note both issues apply to Obi as well as regular Unity physics. At its core, it applies to literally all existing physics engines. Solutions:

- Use primitive colliders (boxes, spheres, capsules, etc) or at the very least, colliders that define a volume. For Unity rigidbodies this means using convex mesh colliders, and for Obi it means using distance fields (http://obi.virtualmethodstudio.com/manual/6.2/distancefields.html) which are both faster and cheaper than MeshColliders. MeshColliders are the most expensive type of collider by a large margin and should be avoided if at all possible.

- Move objects around using forces or rigidbody.MovePosition. This imparts a velocity vector to objects, which allows CCD to do its work.

Again, the common name for this issue you're experiencing is tunneling. Here’s a video I did on this subject:

 

Thanks! I was indeed moving my meshes using the editor gizmo. Although, I can't find the Obi Kinematics Velocities component you've mentioned in the end of the video.

 

Since 6.0 this component is integrated with ObiRigidbody, if you move a kinematic rigidbody a velocity value will be calculated. Note this is just a workaround, ideally you should use forces to move stuff (rigidbodies, actors) around if you intend collisions and other constraints to work properly.

 

Thanks! This helped.

A couple more questions:
If I create a curtain and use particle attachment to "close" it, I get this shape:

Spoiler: Not what I want

However, if I set Max Compression to ~ 0.5 in the distance constraints, I get the nicely folded curtain (the right one in the screenshot below). Though, I can use it only when it's closed because the open curtain (the left one in the screenshot below) with the same compression looks ugly. Is there any other way to achieve such folds without using the max compression setting? Or can I change its value in runtime via script when the curtain is being closed/opened?

Spoiler: What I want

And also, I've noticed strange update behaviour. When I move the clothes, its vertices move a bit...sporadically. And they freeze a bit abruptly. Semetimes it may look like unity itself froze, but it's just the simulation decided that it's time to finish. And it always feels like some vertcies could use a few more simulation iterations, because they freeze in such positions that wouldn't be realistically possible because of the gravity and momentum. I can't say that they freeze in mid-air, no, the simulation do looks kinda-sorta finished at the right moment, but there's always the feeling that it needs a bit more movement to get in the right place. If you don't understand what I'm talking about I can try to capture it on a video. Here are gifs:

Spoiler: Gif1

https://gyazo.com/849c480d2f697bd00707e93463de6a31

Spoiler: Gif2

https://gyazo.com/f3ab3f546015b04218092755be29f3c3

 

You might want to try and increase bend constraint's "max bending", or "bend compliance". These directly control how the cloth bends and folds. See:
http://obi.virtualmethodstudio.com/manual/6.2/bendingconstraints.html

Distance constraint's "max compression" allows particles in the cloth to get closer to each other. This does affect folds but only as a side effect.

You can change *anything* via script. . Do:

Code (CSharp):

1. cloth.maxCompression = 0.5f;

See the API docs for details.

Your solver's sleep threshold is simply too high. Set it to a lower value. See:
http://obi.virtualmethodstudio.com/manual/6.2/obisolver.html

 

Thanks! Unfortunately, any value of bend constraint's doesn't really affect the folding in comparison to a completely disabled bend constraint's. Moreover, bend constraint's + self-collision in such case cuts fps in half, when the curtain is folded. Bend constraint's + self-collision + surface collisions and I go from 150 fps to 20 fps.
I noticed that using surface collision + self collision generally results in "the more folds you create the less fps you get". Is there a way to use surface collision for other objects and disable it for self collision?

Also, is it possible to adjust cloth to a certain position via simulation and somehow store the result (not modifying the initial mesh), so during the next runtime the simulation starts from this state?
For example I want to pin the curtain in the middle like this

Spoiler: example

so when the player first encounters it, it will be in this state. But then it can be unfolded to its initial state (just hanging plain peace of fabric).

 

Question About Obi Cloth Initialization (Obi Cloth Behavior on First Play)

Whenever I first Press Play in a scene containing Obi Cloth Flags blowing in the wind - the flags go crazy at first and then slowly settle down to use the wind force I set in the Inspector.

1.) Is this normal?
2.) If not normal, what could possibly be causing such a behavior?

 

Nope. Never had any user report something similar to what you describe.

Without any details regarding your setup, it's hard to tell. Simply adding a cloth and a force zone does not result in this behavior. You can see this in the "Wind" sample scene, there's two cloth flags and two wind sources but (at least for me) it works fine.

Please write to support(at)virtualmethodstudio.com providing more details about your scene: what kind of cloth it is (regular, skinned or tearable), what simulation backend you're using, Unity and Obi versions you're using, etc.

 

Thank you for your sanity-checking reply. I will build a sample project and send to official support.

 

Hello is Your system working ok with Unity LOD group?

 

Hi,

Obi is a physics engine, if you add/remove particles from the simulation based on LOD the results will change (think about adding/removing rigidbodies from a scene based on LOD, doesnt really make sense). So no, LOD is not supported, sorry! :/

 

Hi @arkano22 !
First, thanks for these assets, they are really work of art. Love them all (and have them all).
Now, the annoying question: Obi Fluid and HDRP? Is it something you are still planning or completely dropped the ball on it?

 

Hi Lurking Ninja!

Thanks for your kind words.

For now I just dropped the ball on "proper" HDRP integration. There's been several attempts and spent an entire year on this, but came to the conclusion that is just not doable as things are now. ShaderGraph is not nearly flexible enough to do it, and hand writing a non-trivial HDRP shader with lighting integration is simply unfeasible.

So the next thing I'm trying is a poor-man's version: grab the data of one directional light, and do my own basic phong shading on it in screen space. This is less than ideal but at least will allow something to be rendered when using HDRP.

 

Hi there,

Currently working on Obi 6.4, I'm focusing on small, quality of life improvements for editor tools and looking for feedback. Most of these changes/new features are driven by user suggestions, so chances are there's still someone out there who would like to see some specific tool improved or new tools added in upcoming versions.

Here's the relevant post in the Obi forums:
http://obi.virtualmethodstudio.com/forum/thread-3297-post-11740.html#pid11740

let me know your thoughts!

 

Hi, I have a promlem.

When I use obi mesh renderer, if I cut the rope, obi mesh renderer does not work on the cutted part.

If I use chain renderer it's fine, but I want the mesh to bend. Therefore chain renderer is not suitable.

 

Quoting the Manu

Hi! Just quoting the manual here:

http://obi.virtualmethodstudio.com/manual/6.3/roperenderingmodes.html

 

I know how hard the rematching shapes is, but as I saw someone that got, tons of years ago, cutting uFlex softbodies (which is similar to Obi's volume shape matching)... did anyone get any approach to cut through obi softbodies?

I got "plane based cuts" working by disabling the solver update -> cut the mesh with mesh slicer-> recreate the softbody for the new generated parts, but I would like to get something like:

I checked tetrahedralizing meshes with ftetwild + gmsh + vtk as the obi author said, but the process is WAY worse than you even might think and it's windows only, as there's no cross-platform softbody solution excepting Obi.

Any idea regarding obi softbodies for cutting?

 

Hi, Is the forum down?

Thanks

 

Hi!

Not that I can tell, I’m able to access it just fine and our hosting provider reports no recent downtime.

try to access it again, let me know if you still can’t get to it.

cheers,

 

It's down for me. Tried a website called downforeveryoneorjustme ....and it says your site is down. I'm having trouble with skinned meshes and it doesn't help that your documentation is online only -_- ...

 

Hi!

Seems up for me, here’s the link to softbody skinning in the docs:
http://obi.virtualmethodstudio.com/manual/6.3/softbodyskinner.html

Could have been a momentary hitch in our hosting provider. FYI, you can download the documentation in pdf format using a variety of tools. I’ve done this in the past with Unity’s own docs to read them when I don’t have internet access.

let me know if I can be of further help.

 

It is down, been down for awhile. It gets up sometime, but goes down again. Tried using VPN from different countries and using Tor, too.

 

It's always been up. It's just not secure due to the lack of SSL certificates

 

Hi there, question if ok, when will you plan to update the fluxy asset, I see this version on youtube

but will we ever get it? Please can we get that, I'd love to get the sallow water sim part (hopefully for BIRP not URP etc)!

 

Hi,

It’s still under development, will be released during the first quarter of 2024, not possible to give an exact date yet.

Physics will work for all render pipelines, as usual. Most of the sample scenes will use shaders authored for URP, though it should be simple to convert them to BIRP (most of the time, just a matter of adding “built-in” as a compilation target in the shader)

Kind regards,

 

No, it doesn't, after accepting connection without ssl it just shows "site not found".

 

That's very strange. I use both the manual and the forums multiple times a day without issue (new posts keep being added to the forum by other users), hosting provider reports no downtime in the past few weeks. Checking site status with several webpages/utils shows it's up:

 

What’s the exact URL you are trying to access? What country are you accesing it from? Are you using VPN?

Do these work for you?
http://www.virtualmethodstudio.com
http://fluxy.virtualmethodstudio.com/

 

Looks like you have some kind of weird setup. It always worked for me...

 

The first one works, the second one doesn't the same as the documentation.

Tried VPN from different countries, I am connecting from Russia. Nothing helps. It did work for some time, but then stopped again, haven't been able to open the site for more than two weeks now.

 

I'm not the only one with this problem and I don't have any weird setup, whatever that means.

 

Domain and physical hosting are the exact same for both urls, only difference is that the second one is a subdomain. If you can access the first one but not the second, it is definitely a problem on your end. Maybe a dns/caching issue?

obi.virtualmethodstudio.com just points to:
http://www.virtualmethodstudio.com/obi/

same for the manual:
http://www.virtualmethodstudio.com/obi/manual/6.3/

Can you access either one?

Just tried using a VPN to connect from Russia, still works fine for me.

If the issue persists and you still can’t access the website, let me know and I’ll send you the manual in pdf format so you can consult it in the meantime. Our support email is also available for support requests in case you can’t use the forums either.

kind regards

 

Maybe the issue is related to the ssl certificate which seems to be invalid for the subdomain?

 

Apparently not, the user said:

Anyway, afaik regular (ie, not wildcard) SSL certificates work for a specific domain / subdomain. Currently, only the domain is protected using SSL, but that shouldn't intermittently prevent a specific user from accessing the subdomain?

 

I managed to connect using Tor, so no need, thanks for the help

 

We have added a wildcard SSL certificate that extends to all subdomains of www.virtualmethodstudio.com, in case the lack of SSL certificate for the subdomain had anything to do with the issue as Nehvaleem suggested.

Let me know if I can do anything else to help!

 

Now it works!

 

Any news regarding Obi 7.0?

 

It's been in beta since May. You can request access to the beta by writing to obi+beta@virtualmethodstudio.com, stating your invoice number.

During the first couple months of beta testing, quite a few bugs and usability quirks were reported that eventually led us back to the drawing board to redesign some aspects of it. The beta was updated a couple months ago with quite a few changes and so far things are going smooth, we're going to give it some more time for reports to come in (probably around one more month) while we keep doing internal stress tests and refining documentation before launch.

Here's what's new:
http://obi.virtualmethodstudio.com/manual/7.0/whatsnew.html

 

Oh wow, so this is confirmed that Fluids going to support HDRP? Since it was our main drawback

 

Yes, they do support HDRP. Fluid rendering is done by generating a mesh, so you can use regular materials on it. The only limitation is that the vertex shader must decompress vertex data, since we store normals using octahedral projection. This is easily done using Shadergraph and a node that does this for you is included with the asset.

 

Hello, I am using the latest obi, but I encountered a problem. When there are multiple OBI Rope in my project, it will be difficult to run webGL when publishing. Why? Please help me, thank you

 

Hi,

Unity's Burst compiler does not support WebGL. As a result, any Burst/Jobs code run on WebGL will use a single thread, using no vectorization.

This is mentioned in the asset's description, its manual, faq, and Burst's manual as well:

 

No, not unless Unity decides to add WebGL support to the Burst compiler. Unfortunately it's not in our hands to do anything about it.

 

ok thank you great author