Eevee: Modulo node behaves unexpectedly/inconsistently #68687

New Issue

Niek Sprakel · 2019-08-15T11:22:42+02:00

Niek Sprakel commented

2019-08-15 11:22:42 +02:00

System Information
Windows 10 Professional (x64) Version 1903 (build 18362.267)
Graphics: Intel(R) HD Graphics 630

Blender Version
v2.80.75

Here is an attached blend file that illustrates the issue (visible in render preview as you switch between eevee and cycles).

If you compare the outcome of mod(2x, x) between eevee and cycles. Cycles seems to correctly evaluate that to 0 while eevee seems to evaluate that incorrectly to 1 for many values of x (for both integers and fractions).EeveeModError1.blend
The bug also occurs for mod(yx,x) for many values of y (I've tested it for a couple of integer values of y).

System Information Windows 10 Professional (x64) Version 1903 (build 18362.267) Graphics: Intel(R) HD Graphics 630 Blender Version v2.80.75 Here is an attached blend file that illustrates the issue (visible in render preview as you switch between eevee and cycles). If you compare the outcome of mod(2*x, x) between eevee and cycles. Cycles seems to correctly evaluate that to 0 while eevee seems to evaluate that incorrectly to 1 for many values of x (for both integers and fractions).[EeveeModError1.blend](https://archive.blender.org/developer/F7665603/EeveeModError1.blend) The bug also occurs for mod(y*x,x) for many values of y (I've tested it for a couple of integer values of y).

Niek Sprakel commented

2019-08-15 11:22:42 +02:00

Added subscriber: @dohduhdah

Clément Foucault was assigned by Niek Sprakel

2019-08-15 11:23:14 +02:00

Brecht Van Lommel commented

2019-08-15 11:36:08 +02:00

Added subscriber: @brecht

Brecht Van Lommel commented

2019-08-15 11:36:08 +02:00

Please verify if this is still an issue in the latest build, I believe there was a fix related to this:
https://builder.blender.org/download/

Please verify if this is still an issue in the latest build, I believe there was a fix related to this: https://builder.blender.org/download/

Niek Sprakel commented

2019-08-15 14:12:58 +02:00

In #68687#753622, @brecht wrote:
Please verify if this is still an issue in the latest build, I believe there was a fix related to this:
https://builder.blender.org/download/

Yes, I've tried it today with the latest build. There have been a few fixes, but there still appear to be problems with the modulo function in eevee.

I notice them in a more complicated setup when comparing the results between eevee and cycles:

https://blenderartists.org/t/confusion-about-color-difference-between-eevee-and-cycles/1173638

I use the modulo function in the shader nodes to generate color combinations:

https://i.imgur.com/BBqAsgv.png

Switching between cycles and eevee in rendered preview causes certain elements to take on completely different colors (while most of the colors remain equal).mod-grid2.blend

> In #68687#753622, @brecht wrote: > Please verify if this is still an issue in the latest build, I believe there was a fix related to this: > https://builder.blender.org/download/ Yes, I've tried it today with the latest build. There have been a few fixes, but there still appear to be problems with the modulo function in eevee. I notice them in a more complicated setup when comparing the results between eevee and cycles: https://blenderartists.org/t/confusion-about-color-difference-between-eevee-and-cycles/1173638 I use the modulo function in the shader nodes to generate color combinations: https://i.imgur.com/BBqAsgv.png Switching between cycles and eevee in rendered preview causes certain elements to take on completely different colors (while most of the colors remain equal).[mod-grid2.blend](https://archive.blender.org/developer/F7665821/mod-grid2.blend)

Mark commented

2019-08-26 18:13:48 +02:00

Added subscriber: @GpuDevil

Mark commented

2019-08-26 18:13:48 +02:00

This is likely a floating point precision issue regarding GLSL's implementation of mod() and GPU code generation, see this thread: https://www.raspberrypi.org/forums/viewtopic.php?t=189455

This is likely a floating point precision issue regarding GLSL's implementation of `mod()` and GPU code generation, see this thread: https://www.raspberrypi.org/forums/viewtopic.php?t=189455

Clément Foucault commented

2019-08-27 01:48:24 +02:00

Seems like the issue with mod(x,x) != 0 isa regression. However, the imprecision pointed by @GpuDevil is likely to remain as it is an implementation behavior we cannot ensure. And I tried expanding the terms and it did nothing.

blender-admin commented

2019-08-27 01:49:36 +02:00

This issue was referenced by d9be59e872

This issue was referenced by d9be59e872f8a112f31b73f07fe41efb51a08ad9

Clément Foucault commented

2019-08-27 01:50:19 +02:00

Changed status from 'Open' to: 'Resolved'

Clément Foucault closed this issue

2019-08-27 01:50:19 +02:00

Eyad Ahmed commented

2020-02-28 01:37:43 +01:00

Added subscriber: @IyadAhmed

Eyad Ahmed commented

2020-02-28 01:37:43 +01:00

I still see the problem in 2.82, it occurs whenever there are negative numbers as input for both Vector Math and Math nodes modulo, EEVEE seems to be more accurate, it is the Cycles implementation that doesn't produce desirable results.

Brecht Van Lommel commented

2020-02-28 14:31:15 +01:00

@IyadAhmed, it's best to create a new report then with example .blend file and system information, to be sure we are looking at the same problem.

Eyad Ahmed commented

2020-02-28 22:52:50 +01:00

In #68687#882150, @brecht wrote:
@IyadAhmed, it's best to create a new report then with example .blend file and system information, to be sure we are looking at the same problem.

Indeed it is not exactly the same problem, however the problem above still exists in 2.82 and blender-2.83-1a1f2912e65e-windows64, screenshots using the above file "EeveeModError1.blend"
EEVEE

Cycles

> In #68687#882150, @brecht wrote: > @IyadAhmed, it's best to create a new report then with example .blend file and system information, to be sure we are looking at the same problem. Indeed it is not exactly the same problem, however the problem above still exists in 2.82 and blender-2.83-1a1f2912e65e-windows64, screenshots using the above file "EeveeModError1.blend" EEVEE ![eevee.png](https://archive.blender.org/developer/F8379020/eevee.png) Cycles ![cycles.png](https://archive.blender.org/developer/F8379021/cycles.png)

Sign in to join this conversation.

No Label

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

Eevee: Modulo node behaves unexpectedly/inconsistently #68687