Geometry Nodes: Using "Input-Value"-node with "Attribute-Math-Divide"-node leads to incorrect results in following "Attribute-Math-Modulo"-node #87564

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Christian · 2021-04-16T16:06:23+02:00

Christian commented

2021-04-16 16:06:23 +02:00

System Information
Operating system: Windows 10 Pro
Graphics card: Geforce GTX 960

Blender Version
Broken: 2.93.0 Beta fa8d566c3b
Worked: none, saw the problem in the three latest 2.93 Alpha versions I tested, as well

Short description of error
The modulo function of the "Attribute-Math"-node leads to incorrect results when applied to a non-rounded division result - even when the division result doesn't have a fractional part. This behaviour only occurs, when one or both float-sockets of the preceding "Attribut-Math-Divide"-node are connected to "Input-Value"-nodes.

Example: (0.004[from value node] / 0.1) mod 2.000 = 2.000 (very wrong!)

Exact steps for others to reproduce the error
Create a simple geometry node tree on an empty mesh:

Mesh-Primitives: Line with just one point
Input-Value-Node: set the Value to 0.400
Attribute Math: Divide (Input Value) / 0.100 => "divRes"
Attribute Math: Modulo "divRes" mod 2.000 => "mod"

The spreadsheet shows the attribute "mod" having the value "2.000". It should be 0.000.
If you insert an "Attribute-Math-Round"-node to round "divRes", the modulo value changes to the correct result.
If you disconnect the "Input-Value"-node and enter the value "0.400" directly, the result is also correct.

Screenshot with and without rounding:

Blend-File:
geo-modulo-bug.blend

**System Information** Operating system: Windows 10 Pro Graphics card: Geforce GTX 960 **Blender Version** Broken: 2.93.0 Beta fa8d566c3b12 Worked: none, saw the problem in the three latest 2.93 Alpha versions I tested, as well **Short description of error** The modulo function of the "Attribute-Math"-node leads to incorrect results when applied to a non-rounded division result - even when the division result doesn't have a fractional part. This behaviour only occurs, when one or both float-sockets of the preceding "Attribut-Math-Divide"-node are connected to "Input-Value"-nodes. Example: (0.004[from value node] / 0.1) mod 2.000 = 2.000 (very wrong!) **Exact steps for others to reproduce the error** Create a simple geometry node tree on an empty mesh: - Mesh-Primitives: Line with just one point - Input-Value-Node: set the Value to 0.400 - Attribute Math: Divide (Input Value) / 0.100 => "divRes" - Attribute Math: Modulo "divRes" mod 2.000 => "mod" The spreadsheet shows the attribute "mod" having the value "2.000". It should be 0.000. If you insert an "Attribute-Math-Round"-node to round "divRes", the modulo value changes to the correct result. If you disconnect the "Input-Value"-node and enter the value "0.400" directly, the result is also correct. Screenshot with and without rounding: ![division-input-value-problem.jpg](https://archive.blender.org/developer/F9935975/division-input-value-problem.jpg) Blend-File: [geo-modulo-bug.blend](https://archive.blender.org/developer/F9935978/geo-modulo-bug.blend)

Christian commented

2021-04-16 16:06:23 +02:00

Added subscriber: @ChristianFrey

Victor-Louis De Gusseme commented

2021-04-16 16:52:33 +02:00

Added subscriber: @victorlouis

Victor-Louis De Gusseme commented

2021-04-16 16:52:33 +02:00

Maybe this is a floating point thing:

0.4 / 0.1 = 3.999... -> shows up in spreadsheet as 4.000
3.999... % 2 = 1.999.... -> shows up in spreadsheet as 2.000
round(3.999...) = 4.0000001
4.0000001 % 2 = 2.00...

Maybe this is a floating point thing: * 0.4 / 0.1 = 3.999... -> shows up in spreadsheet as 4.000 * 3.999... % 2 = 1.999.... -> shows up in spreadsheet as 2.000 * round(3.999...) = 4.0000001 * 4.0000001 % 2 = 2.00...

Christian commented

2021-04-16 20:29:14 +02:00

In #87564#1147646, @victorlouis wrote:
Maybe this is a floating point thing:

0.4 / 0.1 = 3.999... -> shows up in spreadsheet as 4.000

3.999... % 2 = 1.999.... -> shows up in spreadsheet as 2.000

round(3.999...) = 4.0000001

4.0000001 % 2 = 2.00...

I guess, you mean:

4.0000001 % 2 = 0.0000001 -> shows up as 0.000

This could be what's happening, but why is it only happening when using an "Input-Value"-node in front of the "Attribute-Math-Divide"-node?

> In #87564#1147646, @victorlouis wrote: > Maybe this is a floating point thing: > > * 0.4 / 0.1 = 3.999... -> shows up in spreadsheet as 4.000 > * 3.999... % 2 = 1.999.... -> shows up in spreadsheet as 2.000 > * round(3.999...) = 4.0000001 > * 4.0000001 % 2 = 2.00... I guess, you mean: * 4.0000001 % 2 = 0.0000001 -> shows up as 0.000 This could be what's happening, but why is it only happening when using an "Input-Value"-node in front of the "Attribute-Math-Divide"-node?

Christian commented

2021-05-29 12:26:53 +02:00

I just tried the latest version (2.93-beta-release.c36938297753).

The problem seems to be fixed, now:

So I guess, the ticket can be closed.
Shall/can I do this myself?

I just tried the latest version (2.93-beta-release.c36938297753). The problem seems to be fixed, now: ![divModOk.png](https://archive.blender.org/developer/F10148086/divModOk.png) So I guess, the ticket can be closed. Shall/can I do this myself?

Ankit Meel commented

2021-06-15 13:19:36 +02:00

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

Ankit Meel closed this issue

2021-06-15 13:19:36 +02:00

Ankit Meel self-assigned this 2021-06-15 13:19:36 +02:00

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Geometry Nodes: Using "Input-Value"-node with "Attribute-Math-Divide"-node leads to incorrect results in following "Attribute-Math-Modulo"-node #87564