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Hair collision problem
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System Information
Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 430.39

Blender Version
Broken: version: 2.80 (sub 74), branch: blender2.7, commit date: 2019-06-10 23:38, hash: rBa0608340ae14
Worked: (optional)

Short description of error
[Please fill out a short description of the error here]

Exact steps for others to reproduce the error
[Please describe the exact steps needed to reproduce the issue]
[Based on the default startup or an attached .blend file (as simple as possible)]



Event Timeline

You should provide a description of the problem when you submit a bug. Nevertheless I'm guessing the issue is that the hair doesn't collide/interact properly with the cylinder. This is a known problem and the hair system (particularly collisions) is due an overhaul at some point. For now, if you search around the blender community you should find others who've had similar issues and shared their workarounds.

Looks like T59742 Hair instability with collision. Images 3 & 4 seem to be duplicates of 1 & 2.

@iclone (iclone) Would be nice if there was a blend file demonstrating the issue and a short description. I appreciate English may not be your native language, but could you try? Thank you.

I'm afraid this is not an inestability problem, I mean... it is, but it's not a bug, it's due to defaults being wrong, and also the haird collision system not being the best in the world, it's not too precise.

But it works when you configure it properly, I'll try to do a video ASAP about how to configure hair collission properly so you can check again to confirm or discard the bug.


Here is the example with correct settings:

As you can see the collision works, I don't thing this is a bug, it's just that hair has wrong defaults and it's kind of complicated to setup correctly.

@Juan Gea (juang3d) . Thank you very much! I get your point that because it can work it does work. That there are parameter settings out there where the whole ensemble just falls into place. Nice bit of work here - thank you again for putting it together and sharing.

But I could also argue that being "kind of complicated to setup correctly" is a bug in its own right. Big client presentation tomorrow. Entire team is glowering at Osgood: when in the H - E - Double Tooth Picks will he get that damn hair effect done? Useful tools cannot be founded upon sparse islands of stability spread hither and yon over vast stretches of a crazy parameter space.

Along those lines, I'd make the case for T59742 as being the instability bug and this relates to that; that we should strive for well-behaved parameterization. Fractals are pretty to look at, but we should keep them out of our control spaces and give users tractable means to set up their effects.

As a practical matter, I don't think hair stabilization will be realized until the particle system is retooled. Perhaps you'll be a part of that. Usefulness aside, particles make for a nice playpen. Cheers!

I have to disagree.

A simulation system is not an easy thing to use, a bad default settings choice don’t convert a tool en better or worse, and the settings I picked are not weird, they are pretty standard, but knowledge in the Blender particle system and it’s physics are needed to configure it correctly, would you say that the default values in Houdini nodes make Houdini a bad app? I don’t think so.

We can talk about bad defaults or about the ease or difficulty of learning the details on how to manipulate particles and hair in Blender, but that does not make this a bug.

You have to correctly understand what is the correct physics integrator to use it, you hace to understand that you have to configure a more detailed hair so it has enough collision points to behave normally instead of behaving like a bunch of glued sticks and you have to understand to as with any physics system the collision settings have to be correctly configured, none of that makes this a bug.

Can this be improved? Of course, can particles be improved? Of course, are they “half-baked” toys not ready for production? Not at all, so they require a bit of time to correctly understand how to manipulate them? Yes

BTW not knowing a tool and trying to use it before doing a big presentation has never been a good idea, I’m sorry to hear that you are in that situation, try to apply the settings I described in the previous message and give a bit of collision thickness to the collider.

Don’t rush physics simulations, it never works (no matter if you use Houdini, Maya, Max or Blender, I know all of them and the situation is always the same for one thing or another)

I wish you the best of lucks for your presentation.

I owe you an apology @Juan Gea (juang3d) . As to the "presentation," I was writing allegorically - "tongue-in-cheek" if you will. Sometimes I don't make a good estimate of what comes across in writing. As for your points, I do appreciate them and attribute to them significant basis - thank you for sharing them. To my mind, the tradeoff between ease-of-use and minimum-competence-to-use is one we wrestle with in every interaction between people and systems. As fascinating as this subject may be, however, it is off-topic for this bug report and would be better situated in DevTalk or similar discussion forum. I am looking forward to picking up this thread - or others - with you. Take care!

No worries, I agree with you that better defaults would be good for the hair system :)