Cloth simulation compatibility is broken in 2.74 #44157
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Lukas Tönne
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Reference: blender/blender#44157
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System Information
Windows8.1 pro x64, GeForce GTX660
Blender Version
Broken: 2.74TB1(
ed5df50) and later (I've verified with TB1 - RC4 too)Worked: 2.72, 2.73a
Short description of error
When using "Lether" preset of the Cloth simulation, the results are differences between before 2.74 and later.
I just verified this preset, but probably, other presets have also same problem...
Exact steps for others to reproduce the error
See the attached files please.
LetherCloth.blend
Thanks,
Changed status to: 'Open'
Added subscriber: @SatoshiYamasaki
Added subscriber: @JulianEisel
Coud you test the 2.74 RC ? We had some issues that were fixed since the TB1, so maybe it works again.
Yes of course, I've tested with RC4 too...
OK, I'll add the information. thanks,
Added subscriber: @sindra1961
I think that this is a cause like #43911 .
This is the image which carried out blend file attached in 2.73a(sub0).
But I reduce a value so that influence of bending decreases.
There is little influence of bending in new spring code.
By the way, the result is the same even if I set bending to 10000 in 2.74RC4.
2.74RC4
2.73a(sub0)
different_bending.blend
Added subscriber: @LukasTonne
@LukasTonne
So could you please verify once again, lukas?
cloth stiffness scaling is incompatible, too.
2.73a(sub0)
2.74RC4
.blend
untitled.blend
Added subscriber: @lfb3d
@sindra1961 Thank you for the test images regarding the different Bending Stiffness values. I can see the differences you mention. As an additional note: I usually have a hard time seeing a difference in Bending values such as 1.0, 150.0, 10000.0. So I usually tend to use values such as 0.0001, 0.01, and 10.0 to see noticeable differences in the cloth. It's hard for me to tell the differences between cloth's with high bending stiffness values (values > 1.0). Thanks again!
@lfb3d:
This is a value of bending of presets set in blender.
This is the same as an old spring system.
BendingExamp.blend
Added subscriber: @MartinNorris
Hi,
I opened a bug #45084 and have just posted a patch D1454.
I think this also solves this problem
e.g. for 2.75a patched
Best regards
Martin
PS. And also the original post blend ...
Added subscriber: @YAFU
Hello MartinNorris.
I tried the patch and it seems the simulation with the "LetherCloth.blend" file from this report is quite similar between 2.73a and patched 2.75.4 from master.
But with the "flag3_collision.blend" file from the following thread (post #3):
http://www.blenderartists.org/forum/showthread.php?365655-Slow-Cloth-Simulation-in-2-74
the result of the simulation is still very different (although I think it has improved a little in the patched version). I do not know, maybe I'm wrong, but it seems to me much more natural the simulation result with 2.73a. Perhaps a different problem to what your patch fixes?
Hi YAFU,
I tried the flag3 blend with both 2.73a and 2.75a with patch
For 2.73a
And for 2.75a with patch
And for reference 2.75a without the patch
Is this what you get?
I am sorry, but I do not think the patch makes any difference in this situation
Because the material is already very 'light and flexible' the structural coefficients do not effect the simulation very much
All the problems I was trying to solve are related to structural stiffness e.g. #45084 #44157 and #43911
Looking at your BA thread the original problem you identified was the drop in frame rate
Again, sorry, but the patch does not impact this at all.
Maybe you should open a bug just for the frame rate issue?
Best regards
Martin
@MartinNorris, I'm sorry for not having explained well.
In that thread I mentioned two problems, one referred to the fps speed (flag3.blend shared file in post #1), There is already a report:
https://developer.blender.org/T44031
But the other problem I meant is concerning the broken compatibility where the simulation result is different between 2.73a and 2.74/2.75 (flag3_collision.blend file shared in post #3):
http://www.pasteall.org/blend/35062
@YAFU
OK, it is good the performance hit is reported.
I can try some tests to see if it is calculation of the stiffness scaling with bending_damping that is caused the problem {though I suspect not, the change for this calculation is too small}
Do you see the same results in the screen shots I posted?
For the flag under different versions.
It looks to me as though the patch does not make any difference, but that is most probably because the cloth settings for cotton do not have any significant stiffness.
But with the patch you can try different values for the stiffness, for example raise both the structural and bending stiffness {leave the mass unchanged}, and expect a better result than without the patch.
Added subscriber: @RayMairlot
@MartinNorris. Yes, I see a similar result. But it's hard to know if anything changes a lot with that "flag3.blend" file.
Here I have done some testing with the other file involving collision, comparing 2.73a, 2.75.4 and patched 2.75.4. Here videos and files:
https://www.dropbox.com/s/6cjm0g603l6r6qp/Blender%20Cloth%20Test.zip?dl=0
Really I have the feeling that the simulation is correct as happens in 2.73a. So I do not know if this still means breaking compatibility between versions as the title of this report shows.
@YAFU
That is a great illustration of what you mean
I can see that there is a big difference in the simulation
But I do not think it is anything to do with the stiffness, it is something to do with collision
As a test I built a version where kb = cb = ... {these are the structural properties of the cloth}
Essentially reverting the cloth structural properties to the 2.73a state
But this has no effect on the collisions and it looks like the 2.75a simulation
When I have time I will look into the collision code!
Ok, thanks Martin.
An observation. As I said, the result of the simulation with 2.73a is what I think is right. The only thing I find weird with 2.73a is that the result after the rebound seems in slow motion. But I have found this changes and get little better when increase the value of "Steps" in Quality. The simulation with 2.75 also improves when this value is increased, but the simulation result still seems different and worse than 2.73a to me (although fps between 2.73 and 2.75 seem a little more paired with large values in quality "Steps").
Anyway, just using that same .blend file with these same values, the simulation does not result similar between versions.
Added subscriber: @Blendify
I think this was fixed today am I correct?
Hi @Blendify
At least the cloth stiffness and bending is fixed so it is the same as previous version of Blender
But @YAFU has also indicated that the cloth collision is different and patch D1454 has not touched the collision code
Perhaps the original poster @SatoshiYamasaki can comment if the patch is sufficient for the original problem?
And then we could track a different more specific bug for the cloth collision being different.
Best regards
Martin
Added subscriber: @bireos
Added subscriber: @JuB
Added subscriber: @angavrilov
I did a bisect to find what causes the difference in cloth collision behavior between 2.73 and 2.74/current, and found that it's commit
c6e5f6afe0, which changed the code used by cloth to solve equations. However, it turns out that it most likely didn't introduce any bug . In fact, actually the 2.73 version of the code was exiting the iteration too early to produce a precise solution. Changing the old code to always do 100 iterations makes it produce results close to what current solver does.Thus it seems that cloth collision in 2.73 was more stable simply because imprecise solutions for spring equations somehow resulted in unintended dissipation of energy in the cloth; but the current solver does more iterations, so that doesn't happen. This increase in iteration count may also explain #44031.
Added subscriber: @purpleskydev
Added subscriber: @brecht
Changed status from 'Open' to: 'Archived'
Cloth bending was revamped in 2.8, this bug is no longer relevant.