The "Vector Rotate" shader node behaves differently in Cycles and Eevee #88088
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Reference: blender/blender#88088
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System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce GTX 1660 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 457.63
Blender Version
Broken: version: 2.93.0 Beta, branch: master, commit date: 2021-04-16 16:41, hash:
b2a0f69275
Short description of error
When passing in a (0, 0, 0) vector as the rotation axis of a Vector Rotate node in Axis Angle mode, the return vector is different in Cycles and Eevee. In Eevee, the original vector is returned with no rotation applied. In Cycles, an empty vector of (0, 0, 0) is returned.
User Story
I was attempting to create a shader involving rotation of a coordinate on an axis based on the z component of a face's normal. In Eevee, everything worked fine, but in Cycles, the parts of my meshed that were vertical (zero z component of normal) broke. After some testing I discovered the inconsistency I pointed out above.
Either of these behaviors would be valid if it was consistent, but the inconsistency caused me a great deal of confusion. I would prefer for the Eevee behavior to present for both, as I find it to be more useful.
Exact steps for others to reproduce the error
From the default startup file, apply a material to the cube.
Go into the shader editor for that material.
plug a vector rotate node into the material output.
set the vector rotate's axis to (0, 0, 0).
plug object coordinates into the vector input of the rotate node. (this is not directly related to the bug, it just makes it much easier to see what's going on)
Switch between Cycles and Eevee render engines to observe the changes.
Added subscriber: @StevemBuko
Added subscriber: @CharlieJolly
The code appears to be ok. I wonder if it is a precision issue?
Cycles normalises the Axis before passing the variable. OSL normalises the Axis in the rotate function.
Added subscriber: @lichtwerk
Changed status from 'Needs Triage' to: 'Confirmed'
Wondering how much sense it makes to rotate around a zero axis?
Reading the code @CharlieJolly posted it looks like Cycles should just return the in vector in this case?
Instead, this asserts for me (this is why I'll confirm for now):
This issue was referenced by blender/cycles@429ab9eeff
This issue was referenced by
765406cb51
Changed status from 'Confirmed' to: 'Resolved'