View Full Version : Sewing/ripping apart in Bullete Dynamics

08-24-2015, 02:01 PM
Hi there,

Is this possible? with cloth fx it was really easy but it does not seem to be possible with bullete dyn.

Generally, is Bullete a perfect alternative for cloth fx or there are still certain things that cloth fx is better option?

Thanks in advance.

08-24-2015, 02:33 PM
I wasn't sure but since I'm on my lunch break I thought I'd give it a shot:


It kinda works but I think I need to spend a lot more time on this to see if it's really practical. Basically, the 'cloth' is set to Deformable and the 'knife' is set to Kinematic. There's a weight map called 'activeArea' on the cloth for the Mesh Filter. There's nothing fancy in the settings:


This is just a five minute 'starter' setup but I have to admit I was surprised it worked this well without really doing anything to it yet.

I'm skeptical that in this case it will work as well as ClothFX but now I'm curious. :)


08-24-2015, 02:54 PM
Just wanted to add that I still use ClothFX but mostly just for scanning to use the FXMetaLink tools.

For actual dynamics, I prefer to use Bullet. However, I don't know if Bullet can do this one thing as well yet.

Will take a deeper look at this tonight.


08-25-2015, 02:09 AM
Would you please upload this scene? if it is not a bother and when you have time of course.

I guess you unweld the midline of the cloth object here.

I tried to rebuild according to ur descriptions and params in the images and kinda of works.

08-25-2015, 08:10 AM
Oh, yes, unweld the middle part. Sorry, I should have mentioned that.

I haven't had the chance to go any farther with the test yet. I was hoping to have something more developed before posting files but I'll post that 'starter' scene later this morning. I'm skeptical that this can really work in Bullet but maybe somebody else can make something proper out of it.


08-25-2015, 09:58 AM
Another effect that Cloth FX is still adept at is making effects like foot prints in the snow ... Bullet, as far as I can tell, does not allow a way of controlling 'plasticity' especially with history (e.g. Houdini)

08-25-2015, 10:37 AM
I got into work a little early this morning and spent a few more minutes on this. Basically, I uprezzed the cloth and made a few settings tweaks. Nothing fancy.

129479 129480 129481

In motion, it's really more like ripping than cutting though. This is a fun 'quick and dirty' test but I don't think it's possible to make this effect look really convincing with the current Lightwave Bullet. Maybe if this example was submitted to LW3DG, they can add features to make this work better for this particular effect.


In the meantime, I think ClothFX is still more suitable for this type of effect. I'd love to be proven wrong though. If you can get something more convincing out of this using Bullet, please post what you learn. :)


P.S., I think you would need something like Glue for cloth? But Glue isn't available in Deforming mode. Just thinking out loud.

08-26-2015, 01:28 AM
I can not prove u to be wrong but I can only say that bullete is way faster than cloth for this type of effect. I can assure you that cloth fx is sort of useless when it comes to high-res subdivided objects.

I am now working on every aspect of this effect (it is really necessary for me) and I will give you a more detailed report.

Also the scene that u send will help a lot. I agree that it looks more like ripping. plz give me a few days dear Greenlaw.

08-26-2015, 01:35 AM
I agree that LightWave Bullet is absolutely faster than ClothFX but speed is not the question. ClothFX has the features to do this specific task and Bullet does not. That said, if you can make it work within the existing Bullet features, that would be fantastic!

Good luck and please post what you find! :)


08-26-2015, 02:44 AM
Just for kicks, here's the same 'starter' scene but using ClothFX.

129489 129488 129487

The calc times are actually pretty decent--only a few seconds on my tablet computer. Note that there's a 100 frame preroll to settle the cloth...although, due to self collision, the cloth never really settles. Now I remember why I don't miss ClothFX too much. :p

If that's a problem, you could simply hold a still frame in the MDD data until the cut event occurs.


I hope this helps. Have fun!


08-26-2015, 02:55 AM
BTW, the seam has always been a problem for effects like this. I've never been quite sure what to do about that in cg so I don't sweat it. Instead, I always just patched an 'uncut' render over the 'cut' render in comp and hand track a soft mask to reveal the cut.

Yes, it's a cheat but the end result works, and I get home in time for dinner. :)


08-30-2015, 12:39 AM
Fellas, this is getting more and more confusing as I am exploring.

Greenlaw, Bullet is not a lot better than clothfx in calculation time when u activate self-collision. maybe not very important for most cases but it will be of importance about high-res subdiv objects.

I was stupid and taught maybe bullet does not respect morphing but it does so thanks god.

Is there such a thing as delaying (or setting start of the simulation) for bullet? it seems that it starts to act as soon as we play. this will not be so important when we have another object colliding with deforming body for example but when it comes to self-collision it makes problem. it shows premature ripping/deformin stuffs.

I have a stupid question which might seem off-topic a little but can we make weight maps animatable? I am trying to use an animated weightmap to have more control but it does not seem to be possible to key the weight map values. I hope I am wrong and there is an easy way to set keys on values of weight map.

08-30-2015, 02:20 AM
Is there such a thing as delaying (or setting start of the simulation) for bullet? it seems that it starts to act as soon as we play.
Those are two separate things you're asking.

To offset the global start time, look under the World tab and enter frame for Start Offset. This is typically used for pre-roll but it can be used to delay calculations as well.

For interactive activation on a per item basis, look under Item > Activation > Iniital Activation. Start Active is the default. There are three other options but I usually like use Activate On Last Key which holds off calculation until the time hits the last keyframe on the object. It's very useful if you really want to orchestrate the simulation as opposed to just letting things happen. Be sure to read the manual--Bullet is really pretty simple to use and all this info is covered there.

This is just my personal opinion but I still think Bullet is faster and easier to set up for most 'everyday' situations. But there are indeed areas where ClothFX does do a more precise job; and in some cases, like stitching and cutting, where it's the only appropriate option in LightWave. But this is based on my own scattered experiences with these tools for commericials and film: hair, flags, netting and ropes, or breaking things. I've used it for clothing but only for fairly specific situations. I have to confess, I don't feel I've used the tools consistently enough to have really mastered them, and I don't always rely entirely on the simuluations either--I can recall a handful of situations in the last two years where I used Chronosculpt to alter the results to get exactly what was was called for.

Your own simulation requirements and standards might be very different from mine so I can't guarantee they'll work for you. In the end, the tools you choose should depend on what you need the sim for, and how much time you have for the project.

BTW, you might also consider Syflex for Lightwave. The plugin recently got a huge price reduction. There are a few technical limitations but other users are saying it's the most accurate of the three. Do a search for Syflex in the forums for more info. TBH, I haven't used it for production work myself yet so I can't offer much help with it. I don't think it has an equivalent for ClothFX sewing tools but hopefully another user can provide more informed comments for it.

I have a stupid question which might seem off-topic a little but can we make weight maps animatable? I am trying to use an animated weightmap to have more control but it does not seem to be possible to key the weight map values. I hope I am wrong and there is an easy way to set keys on values of weight map.

In Bullet, I believe weights are treated as single bit data in the Mesh Filter, so the value is either on or off--there is no falloff. This makes it good for pinning points but if you need variable control, you need to use a Gradient set to Weight Map mode or use a grayscale texture in Shape Retention or other shape affecting properties to control falloff of the effect. However, I don't think this is keyframeable in the normal gradient panel.

Now, this next bit is mostly untested by me: The weight map or image is basically acting as a mask so maybe you can keyframe the values using an envelope--this is a way to make the strength of the effect 'keyframeable' across a ramp. Or, if you're using textures, you might animate the positions of the textures in space or maybe even use and image sequence. You might even combine animated layers for more complex patterns. I suspect that's not actually going to work but it might be worth a shot. Try it with something very simple first just to be sure.

(Actually, I do know that gradients/weights works great for very long hair because I usually want the upper range of hair to be fairly static where it lays over the top of head but I also want the lower parts to sway--a graduated weight map in Shape Retention works great here. However, while I've used different constant strength values depending on action in the scene, I've never tried animating the values over time--just never needed to.)

Anyway, that's probably the extent of what I know on the subject. Hopefully somebody with more consistent experience and knowledge will drop in.


08-30-2015, 05:54 AM
I cant thank you enough Greenlaw, I think I took too much of ur time. you gave me detailed and definitely helpful instructions.

I took advantage of "activate on last key" (sorry I cant remember the exact name bec my lw is calculating while I am writing very texts) and it totally worked.

If you are not angry with me yet then may I plz ask a couple of small questions?

There is no start offset under world tab. were u talking about lw 2015 (which I don't have yet)?

Would you also plz give me some hint on setting weight map through other things than painting or weight map assigning tools (w button in modeler)?

Imagine if we can animate weight maps and use it as shape holder. it would really be great and will bring lots of new possibilities.

No need to spend too much time, just give me a hint on how to start plz.

again, thank you so much for help, I am getting really nice results dear G.

08-30-2015, 12:02 PM
Not angry at all. Sorry if I sounded that way. It was really late in the evening when I typed the last post, I was super tired and I still had a lot of work ahead of me, so maybe some crankiness came through in my writing. :)

Regarding the Frame Offset parameter, you're right, I'm using LightWave 2015.3 here. I just now checked 11.6 and it does appear the Offset feature was added in the first 2015 release last winter. (How quickly we take new features for granted. :p) Previously, if I needed to offset a Bullet simulation, I would just offset the MDD data (you'll need to bake the sim before rendering anyway.) But of course that may not apply to your situation because it sounds like you want to offset the calculation to have more control over specific item activation. In 11.6, the Item > Activation controls is probably what you want to work with.

The following tip might not be relevant to what you're doing since I don't think you're using Parts, but Deactivation usually doesn't work very well with many pieces in a single layer. I think this is because some tiny part will probably always be self colliding with another part or falling into infinite space, so the whole object never really gets a chance to 'goes to sleep'. I believe this what causes the jitters that you may have seen some users complain about. If you see this kind of jittering in your sim, the proper way to prevent it is to avoid using Parts and to use separate objects/layers for the individual pieces of your object instead. That might not be relevant here but since you're playing around with different Activation states, I figure you should at least be aware of it.

Also, as far as setting up weight maps, masks and envelopes, I'm not sure what to suggest since I really don't know what you're trying to accomplish. In general, the simplest thing is to weight your object with the falloff values you want, and use that weight map as a gradient mask and then keyframe the values in the envelope--the mask will make the values increase or decrease gradually. For example, if you did this in Shape retention, you can have it hold it's shape and gradually release it in stages. I must be clear that I'm just thinking out loud right now, and this method may not work as described. I'd have to actually try it myself to be sure. And since I don't know what you're doing, it may not even be an appropriate suggestion.

I guess what I'm saying is that there are a lot of different ways to get specific results with Bullet. Because of my usually tight work schedule, I tend to go with whatever solution produces good results but is also the easiest, fastest and most flexible path for getting there. This often means I'm not doing things 'technically correct' but if the results sell a shot, then everybody I work with is happy. Don't be afraid to be 'clever' with solutions and cheat wherever possible. I've always found that if one method is getting difficult or taking too long to complete, chances are I've been trying to do it the hard way--time to come up with a better trick. ;)

I really suggest experimenting with very simple objects and setups that represent small stages of what you're trying to do. Once you understand the requirements for getting the smaller parts of your simulation worked out, then you can try combining the methods. If it's a very complex sim, I sometimes find that it easier to run multiple sims by baking different stages. I find this approach (i.e., not relying to much on '100% simulation-only' solutions,) puts a lot more control in my hands.

Hope this helps.


08-31-2015, 12:33 PM
I was just joking by saying don't be angry bec I had asked too much question. you were perfectly kind and u helped a lottttt.

I think I got what I was looking for. I also cheated on a couple of occasion and I am going to upload what I made.

using texture for shape retention is absolutely good idea and I promise to experiment with it later.

Mr Greenlaw, I am totally aware of falloff for weightmap and this was not my question. plz give me some more time to finish this small work and I will tell u exactly what I was talking about.

I guess everything works fine and there is no huge obstacle unless some unpredicted obstacle arise.

Again, thank you so much for such a detailed response and wit plz for my final result G.

08-31-2015, 12:58 PM
Sure, I hope it works out for you. I'm curious to see what you come up with. :)

09-02-2015, 01:49 PM

this is my first upload in my entire life. this is part of a work and I am going to upload the whole work and my conclusion on cloth fx vs bullet later.

I really thank you G, without you this would have not been possible. I would love to hear ur critics and suggestions.

again thank u so much for being supportive Greenlaw.

p.s. this is accidentally my 100th post. the number 100 is a great and beautiful number from symmetry and number theory viewpoint and I hope this will bring me chance to make great stuffs later.