Attribute Node in Object Mode seems to have undocumented limit of 8 attributes in EEVEE, and exhibits unpredictable behaviour when more are used #92448

New Issue

Dave F · 2021-10-24T13:19:46+02:00

Dave F commented

2021-10-24 13:19:46 +02:00

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: NVIDIA TITAN X (Pascal)/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.68

Blender Version
Broken: version: 2.93.5, branch: master, commit date: 2021-10-05 12:04, hash: blender/blender@a791bdabd0

Short description of error
While using the Attribute node to get float data from Object attributes, there seems to be a limit of 8 attributes, and which 8 you get is not always predictable (leading to some very hard-to-debug behaviour). Perhaps it's related to evaluation order?

Here's a simple bar graph shader with bars linked to the object's custom parameters. As you can see in these screenshots, in Cycles it displays 32 bars (as intended), in EEVEE it only shows 8.

I'm not sure if this is a limitation or a bug. I'd love to have more than 8 (this test uses 32, and my shader requires ~60!) but if that's not possible I think the limitation should at least be listed in the manual, perhaps in one of these:

https://docs.blender.org/manual/en/latest/render/eevee/limitations.html or .

Exact steps for others to reproduce the error

Load the attached blender file bug_shaderProblemB_001.blend
Switch the viewport to Rendered mode
The graph should display the first 32 custom object parameters
Switch to EEVEE

The graph now displays only the first 8 parameters 😿

bug_shaderProblemB_001.blend

**System Information** Operating system: Windows-10-10.0.19041-SP0 64 Bits Graphics card: NVIDIA TITAN X (Pascal)/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.68 **Blender Version** Broken: version: 2.93.5, branch: master, commit date: 2021-10-05 12:04, hash: `blender/blender@a791bdabd0` **Short description of error** While using the Attribute node to get float data from Object attributes, there seems to be a limit of 8 attributes, and *which* 8 you get is not always predictable (leading to some very hard-to-debug behaviour). Perhaps it's related to evaluation order? Here's a simple bar graph shader with bars linked to the object's custom parameters. As you can see in these screenshots, in Cycles it displays 32 bars (as intended), in EEVEE it only shows 8. ![image.png](https://archive.blender.org/developer/F11464373/image.png) ![image.png](https://archive.blender.org/developer/F11464377/image.png) I'm not sure if this is a limitation or a bug. I'd love to have more than 8 (this test uses 32, and my shader requires ~60!) but if that's not possible I think the limitation should at least be listed in the manual, perhaps in one of these: - https://docs.blender.org/manual/en/latest/render/shader_nodes/input/attribute.html?highlight=attribute%20node - https://docs.blender.org/manual/en/latest/render/eevee/materials/nodes_support.html#input-nodes # https://docs.blender.org/manual/en/latest/render/eevee/limitations.html or . **Exact steps for others to reproduce the error** - Load the attached blender file `bug_shaderProblemB_001.blend` - Switch the viewport to Rendered mode - The graph should display the first 32 custom object parameters - Switch to EEVEE # The graph now displays only the first 8 parameters 😿 [bug_shaderProblemB_001.blend](https://archive.blender.org/developer/F11464748/bug_shaderProblemB_001.blend)

Dave F commented

2021-10-24 13:19:46 +02:00

Added subscriber: @df-1

blender-admin commented

2021-10-24 13:19:46 +02:00

blender/blender#92433 was marked as duplicate of this issue

Dave F commented

2021-10-24 13:41:27 +02:00

Interestingly, the EEVEE limit seems to be 8 inputs for Vectors as well as Floats, so by packing the float data into Vec3 you can get 24 values in to the shader, you can see in the screenshot that it handles 24 fine, adding any more doesn't work though

Interestingly, the EEVEE limit seems to be 8 inputs for Vectors as well as Floats, so by packing the float data into Vec3 you can get 24 values in to the shader, you can see in the screenshot that it handles 24 fine, adding any more doesn't work though ![image.png](https://archive.blender.org/developer/F11465203/image.png)

Dave F changed title from ~~Attribute Node in Object Mode seems to have undocumented limit of 8 float attributes in EEVEE, and exhibits unpredictable behaviour when more are used~~ to Attribute Node in Object Mode seems to have undocumented limit of 8 attributes in EEVEE, and exhibits unpredictable behaviour when more are used

2021-10-24 13:58:56 +02:00

RoyTheKoi commented

2021-10-25 18:56:50 +02:00

Added subscriber: @RoyTheKoi

RoyTheKoi commented

2021-10-25 18:56:50 +02:00

It's worth noting that the alpha channel is accessible too, providing a maximum of 4 channels per attribute.

If precision is not a big priority there may be a workaround. I just tested a method that allows packing up to three lower precision values into a single float, theoretically allowing 8x4x3 = 96 unique channels of attributes. The float packing method I used here was adapted from this article: http://emmettmcquinn.com/blog/graphics/2012/11/07/float-packing.html

Note that I'm using 3.0 Alpha which is why custom properties can show as colours, though the main idea should still work for 2.93.

It's worth noting that the alpha channel is accessible too, providing a maximum of 4 channels per attribute. If precision is not a big priority there may be a workaround. I just tested a method that allows packing up to three lower precision values into a single float, theoretically allowing 8x4x3 = 96 unique channels of attributes. The float packing method I used here was adapted from this article: http://emmettmcquinn.com/blog/graphics/2012/11/07/float-packing.html ![Float Packing Attributes.png](https://archive.blender.org/developer/F11496988/Float_Packing_Attributes.png) Note that I'm using 3.0 Alpha which is why custom properties can show as colours, though the main idea should still work for 2.93.

Dave F commented

2021-10-25 19:41:33 +02:00

Cool, nice data packing @RoyTheKoi! Yes I came to a similar conclusion about RGBA, I'm now packing my data into 8 x RGBA channels set to the Raw Data type, for 32 float channels. I managed to split my single shader into two so it just about works for my use case, otherwise I'd have to either use your packed floats approach or split the packed data between custom attributes and vertex data channels. It's a pretty long-winded workaround but hey if it means I can get back to work then I'm happy :-) Thanks!

Richard Antalik commented

2021-10-26 07:16:21 +02:00

Added subscriber: @iss

Richard Antalik commented

2021-10-26 07:16:21 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Richard Antalik commented

2021-10-26 07:16:22 +02:00

I can confirm, that there is limit of 8 attributes. Confirming, since this is undocumented limitation.

Philipp Oeser commented

2021-10-26 14:28:41 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2021-10-26 14:32:57 +02:00

note this limit:

/* Hardware limit is 16. Position attribute is always needed so we reduce to 15.
 * This makes sure the GPUVertexFormat name buffer does not overflow. */
#define GPU_MAX_ATTR 15

Not sure where the others are taken though.

note this limit: ``` /* Hardware limit is 16. Position attribute is always needed so we reduce to 15. * This makes sure the GPUVertexFormat name buffer does not overflow. */ #define GPU_MAX_ATTR 15 ``` Not sure where the others are taken though.

Philipp Oeser commented

2021-10-26 14:33:53 +02:00

Related D12969: Eevee: support accessing custom mesh attributes

Related [D12969: Eevee: support accessing custom mesh attributes](https://archive.blender.org/developer/D12969)

Michael Schieber commented

2022-02-22 11:05:18 +01:00

Added subscriber: @Hetarek

Christoph Werner commented

2022-04-29 10:57:50 +02:00

Added subscriber: @ChristophWerner

Christoph Werner commented

2022-04-29 10:57:50 +02:00

Is there a way to increase or double the amount of attributes in the future? The current limit can be annoying in production.

Cyrill Vitkovskiy commented

2022-06-02 14:37:41 +02:00

Added subscriber: @Cyrill-Vitkovskiy

FLEB commented

2022-07-11 21:05:39 +02:00

Added subscriber: @FLEB

Aaron Carlisle commented

2022-10-18 02:44:00 +02:00

Added subscriber: @Blendify

Aaron Carlisle commented

2022-10-18 02:44:00 +02:00

Changed status from 'Confirmed' to: 'Resolved'

Aaron Carlisle closed this issue

2022-10-18 02:44:00 +02:00

Aaron Carlisle self-assigned this 2022-10-18 02:44:00 +02:00

Aaron Carlisle commented

2022-10-18 02:44:00 +02:00

This limitation has been documented in rBM9630

PedroRyb commented

2024-01-26 00:12:50 +01:00

It's worth noting that the alpha channel is accessible too, providing a maximum of 4 channels per attribute.

If precision is not a big priority there may be a workaround. I just tested a method that allows packing up to three lower precision values into a single float, theoretically allowing 8x4x3 = 96 unique channels of attributes. The float packing method I used here was adapted from this article: http://emmettmcquinn.com/blog/graphics/2012/11/07/float-packing.html

Note that I'm using 3.0 Alpha which is why custom properties can show as colours, though the main idea should still work for 2.93.

Hi, sorry, is the packing code convertible to Geometry Nodes (no code/drivers)? Thanks. I wanted to implement this but I don't know how to do it

> It's worth noting that the alpha channel is accessible too, providing a maximum of 4 channels per attribute. > > If precision is not a big priority there may be a workaround. I just tested a method that allows packing up to three lower precision values into a single float, theoretically allowing 8x4x3 = 96 unique channels of attributes. The float packing method I used here was adapted from this article: http://emmettmcquinn.com/blog/graphics/2012/11/07/float-packing.html > > ![Float Packing Attributes.png](https://archive.blender.org/developer/F11496988/Float_Packing_Attributes.png) > Note that I'm using 3.0 Alpha which is why custom properties can show as colours, though the main idea should still work for 2.93. Hi, sorry, is the packing code convertible to Geometry Nodes (no code/drivers)? Thanks. I wanted to implement this but I don't know how to do it

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Attribute Node in Object Mode seems to have undocumented limit of 8 attributes in EEVEE, and exhibits unpredictable behaviour when more are used #92448

https://docs.blender.org/manual/en/latest/render/eevee/limitations.html or .

The graph now displays only the first 8 parameters 😿