Mantaflow gas under 2.9 renders very different than 2.83 #79476
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Reference: blender/blender#79476
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System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: Radeon RX 570 Series ATI Technologies Inc. 4.5.13559 Core Profile Context 26.20.12028.2
Blender Version
Broken: version: 2.90.0 Alpha, branch: master, commit date: 2020-07-21 22:05, hash:
607d745a79Worked: version: 2.83.3, branch: master, commit date: 2020-07-22 06:01, hash:
353e5bd749Short description of error
The same mantaflow gas scene taken from 2.83.3 and re-simmed under 2.90.0 results in a very different sim. I can't say which is proper, but the differences are big enough to be problematic in trying to use it or learn to use it. It's as if the 2.83 gas is more buoyant for the same values and the 2.9 stick very close to the original particles throughout.
Exact steps for others to reproduce the error
Sim this scene under each version, saving the caches separately, since 2.90.0 caches don't work at all under 2.83.3
explosionB2.83.blend
Added subscriber: @virtualbri
Added subscriber: @kkjagsir
blender 2.83 mantaflow sim bug,s , nobody fix manaflow problem ,please try blender 2.82a for mantaflow
Added subscriber: @iss
Changed status from 'Needs Triage' to: 'Confirmed'
Doesn't look like #79029 on first glance.
Added subscriber: @sebbas
Changed status from 'Confirmed' to: 'Needs User Info'
I think this is in fact related to #79029. In my first answer over there I explain why fluid in 2.90 looks different compared to 2.83 and 2.82.
@virtualbri Can you check if that post is helpful for you?
Hmm, I'd think if the effect of gravity was less in 2.9 than 2.83 my smoke would be higher and farther away from the source particles, not hanging right next to them. It's almost as if they are not getting the Initial Velocity of the source particles. I can understand the density being different; that's fine.
I did try some versions of emitting from a source object volume and didn't see enough differences between 2.83 and 2.9 to care, so it's now making me wonder if it's particle related.
I'll try to make an even simpler version to see if it I can determine if it's particle or initial velocity related.
So these are sims with the buoyancy adjusted as per #79029.
This is turning off 2.83's Initial Velocity on the particles and comparing it to 2.9 with the new buoyancy settings.
I think 2.9 is ignoring the Initial Velocity on the particles enough to make drastically different looking sims.
{F8745363}test2.8particleemission.blend
Changed status from 'Needs User Info' to: 'Needs Developer To Reproduce'
Added subscriber: @REYNEP
Blender Version:- 2.90.0 Beta, branch: master, commit date: 2020-08-04 18:05, hash:
97be726f93, type: ReleaseComp1.mp4
Do you need anything more from me? Can I check/test anything at this time?
Under 2.90.0 Beta, branch: master, commit date: 2020-08-07 15:11, hash:
a93be410c9turning the Source Initial Velocity up to 50 gets you a comparable sim to 2.83.4 simsAdded subscriber: @renderluz-2
I dont know if this related, but the object velocity in 2.90.1 seems to be broken, all the other sliders on the velocity tab affect how the particles behave, but when I reduce the velocity to 0 or even -200 the particles just emit with the same speed... I may be doing something wrong, but this seems like its related to this bug report, so rather than create a new report I just thought I would confirm that object velocity seems to be off on the test I have made.