Bump node bump converges to different result than displacement bump #98122
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Reference: blender/blender#98122
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System Information
Operating system: Windows-10-10.0.19043-SP0 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.07
Blender Version
Broken: version: 3.0.0, branch: master, commit date: 2021-12-02 18:35, hash:
f1cca30557Worked: (newest version of Blender that worked as expected)
Short description of error
Using the same height map in combination with the bump node gives a different result than using the displacement node with bump only.
When switching between the bump and displacement node one can notice a visible brightness difference in parts of the shape.
What is perplexing however is that upon inspecting the normals used in rendering (switch render pass to normals), they are identical.
So the problem probably doesn't lie in how the shading normals are calculated but rather how cycles uses these.
Exact steps for others to reproduce the error
Principled BSFDNodeNotice the difference, (one receives less light)
test.blend
Thank you and have a great day!
Added subscriber: @tempdevnova
Added subscriber: @mano-wii
Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'
I can confirm the difference.
However they are different nodes and I'm not sure if it's really to be expected that the result to be the same.
So we need information from the #render_cycles team to define if it's a bug or not.
Added subscriber: @brecht
Changed status from 'Needs Developer To Reproduce' to: 'Archived'
Bump mapping is only an approximation, it would be great if it matched displacement exactly but it doesn't.
Changed status from 'Archived' to: 'Confirmed'
I thought this was about actual displacement, but if it's bump from the displacement socket that's indeed not ideal.
"However they are different nodes and I'm not sure if it's really to be expected that the result to be the same." Well the normals that the bump node and displacement node give are identical but for some reason the rendered result isn't.
Added subscriber: @YegorSmirnov
I noticed this long ago as well. Using Bump node looks like some kind of a weird overlay, and not like an actual bumpy surface. Hence I wouldn't recommend using the Bump node at all.
Here's a comparison.
Added subscriber: @baoyu
I downloaded the blend file and noticed that the displacement option is set to bump only. In this situation, could we consider that the displacement is and should be just the same as a bump?
"I downloaded the blend file and noticed that the displacement option is set to bump only. In this situation, could we consider that the displacement is and should be just the same as a bump?" Look at the normal pass of the object using both bump and displacment. Funny thing is they are identical yet the final images aren't.