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Geometry nodes. Attribute mix work wrong way
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Description

System Information
Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: GeForce GTX 660 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 456.71

Blender Version
Broken: version: 2.92.0 Alpha, branch: master, commit date: 2020-12-23 18:13, hash: rBc9efb5424079

Short description of error
Using Attribute Mix produces on Vertex Groups produces incorrect results.

Exact steps for others to reproduce the error

  1. Open the attached file.
  2. Select Result vertex groups in the Object Data Properties

You should notice that at factor 1 the result does not match the input from Painted. The result looks equal at a factor of about 0.58.

As title says.
I am mixing two vertex groups with zeros and random values and Factor=1. So result should be equal to second group.
But it is not.

Event Timeline

I suppose, randomize cause issues.

I don't think this is a bug. If you randomize the attribute to values between 0 and 1 that was formerly all zero and then mix it with another attribute, the result will not be all zero anymore. Could you please explain what the expected result is with regards to the second video you've posted?

@Robert Guetzkow (rjg) even without randomizer I have wrong result. I am mixing 0 and gradient and result is different from that gradient


I expect, mix should work like this custom nodegroup

I can't reproduce the problem with a build based on rB960a0b892c09 2020-12-27 14:55 on Linux. Could you please test this again with a current daily build? You seem to be using a different color gradient for display in weight painting (normally zero is blue), perhaps modified through an add-on? Does this also happen when you start Blender with factory defaults?

My bad, I see the problem now. That is indeed strange, you get approximately equal results at about 0.58.

Robert Guetzkow (rjg) changed the task status from Needs Triage to Confirmed.Dec 28 2020, 2:18 PM
Robert Guetzkow (rjg) updated the task description. (Show Details)
Robert Guetzkow (rjg) updated the task description. (Show Details)