Distribute Points On Faces generates ID integers so big that they create floating point errors down the line. #103325

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Antoine · 2022-12-18T22:14:41+01:00

Antoine commented

2022-12-18 22:14:41 +01:00

System Information
Operating system: Win 11
Graphics card: rtx 2060s

Blender Version
Broken: 3.5 alpha, 3.4 stable

Distribute Points On Faces generates an ID field with extremely large integers which causes rounding errors when they are implicitly converted to floats later in the node tree.

The problem is noticeable in the setup provided. The point IDs are captured on curves so that each spline is filled with the same ID. The curves are then subdivided which causes the IDs to be interpolated for new points. One would expect the new interpolated integers to match their neighbors exactly as all points share the same ID. However due to the size of the integers, the interpolation introduces a precision error and produces very unexpected results.

I'm not sure if this qualifies as a bug because each node works independently as designed, but from a user's perspective the problem looks and feels like a bug. I think the IDs are generated this way to minimize the possible chances of collision? I can't think of a good solution but someone smarter might.

ID integer bugs.blend

Based on the file provided:

make sure the viewer is active
turn the subdivide node on and off

**System Information** Operating system: Win 11 Graphics card: rtx 2060s **Blender Version** Broken: 3.5 alpha, 3.4 stable Distribute Points On Faces generates an ID field with extremely large integers which causes rounding errors when they are implicitly converted to floats later in the node tree. The problem is noticeable in the setup provided. The point IDs are captured on curves so that each spline is filled with the same ID. The curves are then subdivided which causes the IDs to be interpolated for new points. One would expect the new interpolated integers to match their neighbors exactly as all points share the same ID. However due to the size of the integers, the interpolation introduces a precision error and produces very unexpected results. I'm not sure if this qualifies as a bug because each node works independently as designed, but from a user's perspective the problem looks and feels like a bug. I think the IDs are generated this way to minimize the possible chances of collision? I can't think of a good solution but someone smarter might. ![ID integer bugs.jpg](https://archive.blender.org/developer/F14070666/ID_integer_bugs.jpg) [ID integer bugs.blend](https://archive.blender.org/developer/F14070668/ID_integer_bugs.blend) Based on the file provided: 1. make sure the viewer is active 2. turn the subdivide node on and off

Antoine commented

2022-12-18 22:14:41 +01:00

Added subscriber: @AntoineP

Iliya Katushenock commented

2022-12-18 23:22:31 +01:00

Added subscriber: @mod_moder

Iliya Katushenock commented

2022-12-18 23:22:31 +01:00

Will check...

Iliya Katushenock commented

2022-12-18 23:50:36 +01:00

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Iliya Katushenock commented

2022-12-18 23:50:36 +01:00

Added subscriber: @HooglyBoogly

Iliya Katushenock commented

2022-12-18 23:50:36 +01:00

I can confirm that there is an error. Since the attribute originally belongs to curves, it's a little strange that interpolation is still used, which implies factorial blending.
But it's a precision issue and a feature request...
Also, here is an example of how you can make it use a simpler and more reliable interpolation method:

I think this might be a known issue, but for now I'll leave that to you. @HooglyBoogly

I can confirm that there is an error. Since the attribute originally belongs to curves, it's a little strange that interpolation is still used, which implies factorial blending. But it's a precision issue and a feature request... Also, here is an example of how you can make it use a simpler and more reliable interpolation method: ![image.png](https://archive.blender.org/developer/F14071066/image.png) I think this might be a known issue, but for now I'll leave that to you. @HooglyBoogly

Antoine commented

2022-12-19 00:04:31 +01:00

Thank you Illiya, I had come up with this solution as well as a few others like dividing down the ID field or just using captured index numbers. The reason I still decided to submit a report is because this use of the ID attribute seems basic and within its intended use.

Marco referenced this issue

2023-09-07 18:41:11 +02:00

Weird Motion Blur with Simulation Nodes #112061

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Distribute Points On Faces generates ID integers so big that they create floating point errors down the line. #103325