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Eevee-Next and Cycles Shader Displacement Works Differently on Geometry Node Instances #122272

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opened 2024-05-26 03:24:21 +02:00 by kocastle · 9 comments
kocastle commented 2024-05-26 03:24:21 +02:00
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System Information
Operating system: Windows
Graphics card: RTX 4080

Blender Version
Broken: 4.2 Alpha
Worked:

Short description of error
In Eevee-Next, the Shader displacement node can displace geometry node instances differently. This is not the case for cycles where each instance copies the shader displacement of the object it is instancing. This is all done without realizing the instances.

Exact steps for others to reproduce the error
Create a plane with a geometry node tree that distributes points on faces and places instances on points.
Instance any mesh that has a shader displacement, which displaces differently based on it's position. (Make sure to enable displacement in material settings)
Switch the render engine between Eevee-Next and Cycles to compare them.

GrassTest1.blend

**System Information** Operating system: Windows Graphics card: RTX 4080 **Blender Version** Broken: 4.2 Alpha Worked: **Short description of error** In Eevee-Next, the Shader displacement node can displace geometry node instances differently. This is not the case for cycles where each instance copies the shader displacement of the object it is instancing. This is all done without realizing the instances. **Exact steps for others to reproduce the error** Create a plane with a geometry node tree that distributes points on faces and places instances on points. Instance any mesh that has a shader displacement, which displaces differently based on it's position. (Make sure to enable displacement in material settings) Switch the render engine between Eevee-Next and Cycles to compare them. [GrassTest1.blend](https://projects.blender.org/attachments/e64f3e7b-5a47-4bfc-a005-ac0f524def76)
GrassTest1.blend
83 MiB
EveeNext.png
285 KiB
Cycles.png
324 KiB
EveeNext.png Cycles.png
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Pratik Borhade commented 2024-05-26 07:16:58 +02:00
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Hi, could you attach .blend for reference?

Hi, could you attach .blend for reference?
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kocastle commented 2024-05-27 01:47:57 +02:00
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Sorry, here it is:

Sorry, here it is:
GrassTest1.blend
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Pratik Borhade commented 2024-05-27 11:58:49 +02:00
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Thanks, can redo this locally. This is not related to GN instances though. Instead, shader of an object which is used as instance is something to look at.

Thanks, can redo this locally. This is not related to GN instances though. Instead, shader of an object which is used as instance is something to look at.
Pratik Borhade commented 2024-05-27 12:14:59 +02:00
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AFAICS, AffectMask and WindStrength property values are making difference here.

AFAICS, `AffectMask` and `WindStrength` property values are making difference here.
kocastle commented 2024-05-27 21:56:20 +02:00
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By difference, does that mean those two property values are causing the two render engines to displace the instances differently?

By difference, does that mean those two property values are causing the two render engines to displace the instances differently?
Pratik Borhade commented 2024-05-28 05:46:07 +02:00
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Their values to/from procedural textures is causing the change.

Their values to/from procedural textures is causing the change.
Pratik Borhade commented 2024-05-28 05:46:19 +02:00
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cc @fclem

cc @fclem
kocastle commented 2024-05-29 21:09:40 +02:00
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There is no change in values between the two engines though. Even with the exact same conditions, the displacement occurs differently.

There is no change in values between the two engines though. Even with the exact same conditions, the displacement occurs differently.
Clément Foucault commented 2024-05-30 15:12:09 +02:00
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I have to call this expected behavior.

Cycles reuses the geometry acceleration structure (BVH) for each instances. So the underlying geometry has to be the same. But EEVEE do instancing before displacement and then the geometry gets rasterized. So displacement is applied differently in EEVEE.

We could introduce an option to make the displacement relative to the instancing source, but this is likely to introduce overhead and complexity.

So considering this a known issue.

I have to call this expected behavior. Cycles reuses the geometry acceleration structure (BVH) for each instances. So the underlying geometry has to be the same. But EEVEE do instancing before displacement and then the geometry gets rasterized. So displacement is applied differently in EEVEE. We could introduce an option to make the displacement relative to the instancing source, but this is likely to introduce overhead and complexity. So considering this a known issue.
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Reference: blender/blender#122272
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