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Fluid Domain (Liquid mode) - changing "Frame Start" setting for sim causes strange Replay errors
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System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 451.48

Blender Version
Broken: version: 2.83.3, branch: master, commit date: 2020-07-22 06:01, hash: rB353e5bd7493e
Worked: (newest version of Blender that worked as expected)

After changing frame start from default frame 1 to something else (later in time) causes Replay cache problems in playback.
It doesnt show correct sim particle data but old one mixing it with the new sim after the new Start Frame.

Exact steps for others to reproduce the error
Create some simple sim using liquid domain and flow objects.
Run simulation for one time to see results (default 1-50frame)
Go to frame 01 and change domain settings for "Frame Start" to let say frame 25
Hit playback...
Replay is not showing accurate results but broken mixed up cache?

Thx!
Libor

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Event Timeline

Libor Batek (lbatek) created this task.Jul 31 2020, 12:27 PM
Libor Batek (lbatek) added a comment.Jul 31 2020, 12:33 PM

After some thinking, I guess that blender doesnt throw away cached frames after changing sim lenght from frame 1-50 to 25-50 ...the cached frames are still used in 1-25 frame range. They should be thrown away to not use it/display it.

Generally going from longer sim to shorter should clean up cached replay accordingly to not display it when out of range.

L.

Richard Antalik (ISS) changed the task status from Needs Triage to Confirmed.Aug 2 2020, 12:54 AM
Richard Antalik (ISS) added a project: Nodes & Physics.
Richard Antalik (ISS) added a subscriber: Richard Antalik (ISS).
In T79423#988295, @Libor Batek (lbatek) wrote:

After some thinking, I guess that blender doesnt throw away cached frames after changing sim lenght from frame 1-50 to 25-50 ...the cached frames are still used in 1-25 frame range. They should be thrown away to not use it/display it.

There may be other animated elements influencing simulation so cleaning up cache may be necessary, not sure if this is testable with relations currently.

Sebastián Barschkis (sebbas) mentioned this in rB03c2439d96e8: Fluid: Do not show fluid if frame is out of cache range.Aug 4 2020, 11:45 AM
Sebastián Barschkis (sebbas) closed this task as Resolved.Aug 4 2020, 11:48 AM
Sebastián Barschkis (sebbas) claimed this task.
Sebastián Barschkis (sebbas) added a subscriber: Sebastián Barschkis (sebbas).

@Libor Batek (lbatek) I hope I understood your issue correctly. In the latest version of master (03c2439d96e8) the viewport will never show any fluid if the current frame is outside of the cache start / end frame range.
Feel free to reopen if this was not what you had in mind!

Richard Antalik (ISS) added a comment.Aug 5 2020, 2:02 AM

I understood this in a way that if you want to move simulation in time, you just change frame start to later frame, but that will just "not display" simulation.