Liquid Initial velocity is inverted #79748
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Reference: blender/blender#79748
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System Information
Operating system: MacOS Mojave
Graphics card: Intel
Blender Version
Broken: 2.90.0 Beta
Short description of error
Initial velocity is inverted.
Exact steps for others to reproduce the error
test_flow_direction.blend
Water jets up. Initial Velocity Z is -10, water should jet down
Added subscriber: @MBG
Surface Emission doesn't work properlyto "Surface Emission" doesn't work properly. "Initial Velocity" work incorrect."Surface Emission" doesn't work properly. "Initial Velocity" work incorrect.to "Surface Emission" doesn't work properly. "Initial Velocity" works incorrect.And with disabled fluid flow we still have the flow. On the screenshot below "Use Flow" flag disabled on frame 10 but the flow continuing.
Added subscriber: @iss
Changed status from 'Needs Triage' to: 'Needs User Info'
Please upload example file.
Below Z component =-10 (and the default gravity Z component =-9.81):
test_flow_direction.blend
Below Z component =10 (and the default gravity Z component =-9.81):
test_flow_direction2.blend
To apply changes, I update "Cache Directory" every time when parameters changed. But flow direction is random - I can't predict how it will be with the same parameters.
Also, "Surface Emission"=0 doesn't stop the flow, see screenshot below:
test_flow_emission.blend
From https://docs.blender.org/manual/en/dev/physics/fluid/type/flow.html#flow-source
Surface Emission
Maximum distance in Voxels from the surface of the mesh in which fluid is emitted. Since this setting uses voxels to determine the distance, results will vary depending on the domain’s resolution.
I would say, that setting "surface emission" to 0 should not stop flow. Also I can not confirm that values are ignored - I change value to 10 and I get huge blob of liquid.
I can confirm that something is wrong with
test_flow_direction.blendfile. Not sure what though.Please open another report for each new bug. But please check if it is already reported first.
"Surface Emission" doesn't work properly. "Initial Velocity" works incorrect.to Liquid Initial velocity is invertedChanged status from 'Needs User Info' to: 'Confirmed'
Added subscribers: @sebbas, @mont29
The scale of the cube domain is negative on its Z axis...
@sebbas but tooltip says those velocity are in world space. Or is 'world space' here meaning 'space of the fluid domain object'? Looks like it at least, tooltip should be updated then?
@mont29 @sebbas That's not enough to just change the tooltip. Please let's set the Z speed to zero and water still jets up. Scene gravity is equal to -9.81m/s**2, and it's inverted here too. Sure, we need to have the same global gravity direction for all objects! We can't invert gravity direction by any manipulations on physical objects.
I don't see why considering the domain object as the simulation´s world would be bad? It adds a nice level of control for users, and if you want your domain to match Blender´s world, just do not transform it!
In any case, this is design discussion, which has nothing to do here.
@mont29 By your opinion, is it good when global constants have random or unpredictable values for different objects? What are global constants mean in this case?
@mont29 For now, when we use a negative Z scale for liquid domain AND for liquid source too, should be the global gravity direction inverted twice for the source? I just checked it... could you predict the result? Does it the same for planar planes with the so-named checkbox disabled/enabled? And how about the total fluid speed vector for vertically moving source and/or moving liquid domain? Maybe that's obvious for you and you are ready to update all the tooltips with short and clear descriptions for all the cases... Sure, I missed some maybe more complex cases which are results of the global vectors inversion issue too.
@MBG please stop adding noise to this report, as already said, this is not the place to have design discussion, and neither you or me are implicated in actual work on that project. Please wait for feedback from @sebbas
Added subscriber: @HooglyBoogly
Mantaflow (fluid simulator) has no active developer at the moment. Moving those bugs as known issues so at least other users can find their issues already reported.