Vector, RGB, Ramp and other Curve Nodes do not appear to respect spline tangents #113455

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opened 2023-10-09 17:49:14 +02:00 by Nick Dorn · 4 comments

Nick Dorn commented

2023-10-09 17:49:14 +02:00

System Information
Operating system: Windows 10
Graphics card: GTX 1070

Blender Version
Broken: blender 4.0 to 4.1, but likely on all versions of blender, retroactive!
Worked: none

The Vector curve node has not received the spline math fix, that keyframes and the graph editor did. In many situations, this results in sharper gradients than expected, and "bifrucated" gradients/curves whose internal and external tangent both intersect the curve near the handle. This does happen for RGB curves, and I believe this also may affect color ramp too.

Exact steps for others to reproduce the error
just about every vector curves node setup will be affected to some degree, see reference image. (small spacing, and 45 degree angles exacerbate issue.)

This will be a breaking issue for some textures, materials, and geometry nodes. This should be done by blender 4.0 or blender 4.1. It will also "fix" many shaders that were subpar, noticeably some volumetricc shaders and gradient textures that were not as smooth as intended.

**System Information** Operating system: Windows 10 Graphics card: GTX 1070 **Blender Version** Broken: blender 4.0 to 4.1, but likely on all versions of blender, retroactive! Worked: none The Vector curve node has not received the spline math fix, that keyframes and the graph editor did. In many situations, this results in sharper gradients than expected, and "bifrucated" gradients/curves whose internal and external tangent both intersect the curve near the handle. **This does happen for RGB curves, and I believe this also may affect color ramp too.** **Exact steps for others to reproduce the error** just about every vector curves node setup will be affected to some degree, see reference image. (small spacing, and 45 degree angles exacerbate issue.) This will be a breaking issue for some textures, materials, and geometry nodes. This should be done by blender 4.0 or blender 4.1. It will also "fix" many shaders that were subpar, noticeably some volumetricc shaders and gradient textures that were not as smooth as intended.

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Nick Dorn added the

labels 2023-10-09 17:49:15 +02:00

Nick Dorn changed title from ~~Vector Curve Nodes have incorrect spline math~~ to Vector, RGB and other Curve Nodes have incorrect spline math

2023-10-09 17:55:27 +02:00

Iliya Katushenock added the

Nodes & Physics

labels 2023-10-09 17:59:28 +02:00

Richard Antalik added

and removed

labels 2023-10-09 21:03:28 +02:00

Iliya Katushenock removed the

label 2023-10-10 13:05:22 +02:00

Nick Dorn commented

2023-10-13 14:39:31 +02:00

Author

just a question, is this actually part of the UI module? It's not a paper cut or anything like that- the display on the node shows it correctly, too, but the math that goes into it is the issue. Here's a screenshot of it producing a pretty bad (and noticeable) result in geometry nodes. I'm not familiar if all of these nodes use the same math or not, or if the UI spline is the same one that's sampled (?) to get the result?
until now I was under the impression that all spline math in blender was from the same algorithm, so I thought the changes to fix it for the graph editor took place everywhere else.

just a question, is this actually part of the UI module? It's not a paper cut or anything like that- the display on the node shows it correctly, too, but the math that goes into it is the issue. Here's a screenshot of it producing a pretty bad (and noticeable) result in geometry nodes. I'm not familiar if all of these nodes use the same math or not, or if the UI spline is the same one that's sampled (?) to get the result? until now I was under the impression that all spline math in blender was from the same algorithm, so I thought the changes to fix it for the graph editor took place everywhere else.

Untitled.png

247 KiB

Iliya Katushenock commented

2023-10-13 14:46:18 +02:00

Member

Well, that is UI widget function.

Well, that is UI widget function.

Nick Dorn commented

2023-10-16 15:57:06 +02:00

Author

it seems someone noticed this affects the ramp node as well. #108244
it's probably not the whole issue in that case, something else seems to be up, there, too, but upon testing with that file, there is no interpolation which respects the curve's tangents at both the center and approaching other points without causing a sharp edge. It may be smooth in math, but the resolution of the ramp doesn't seem to allow it in the case of a ramp like it would pure math or vector curves, making the effect more obvious.

I think reworking the nodes that contain a spline in their UI is needed- ideally committing all at once or in the same version, because, like I said, it's a breaking change for various materials, geometry nodes setups and other things, and we probably don't want 4.0 to have the fix only in shaders, or 4.1 to be missing a fix in specifically ramp nodes.

it seems someone noticed this affects the ramp node as well. https://projects.blender.org/blender/blender/issues/108244 it's probably not the whole issue in that case, something else seems to be up, there, too, but upon testing with that file, there is no interpolation which respects the curve's tangents at both the center and approaching other points without causing a sharp edge. It may be smooth in math, but the resolution of the ramp doesn't seem to allow it in the case of a ramp like it would pure math or vector curves, making the effect more obvious. I think reworking the nodes that contain a spline in their UI is needed- ideally committing all at once or in the same version, because, like I said, it's a breaking change for various materials, geometry nodes setups and other things, and we probably don't want 4.0 to have the fix only in shaders, or 4.1 to be missing a fix in specifically ramp nodes.

Nick Dorn changed title from ~~Vector, RGB and other Curve Nodes have incorrect spline math~~ to Vector, RGB, Ramp and other Curve Nodes do not appear to respect spline tangents

2023-10-16 15:58:37 +02:00

Gurra commented

2024-01-22 20:37:23 +01:00

Just saw this on Blender Today and yes this is something that have been bugging me for quite some time but haven't gotten around to report. Most of the times I can live with what we have now, but other times this REALLY bothers me since there is no way of getting a curve perfectly smooth. Pretty please do something about it :)

Just saw this on Blender Today and yes this is something that have been bugging me for quite some time but haven't gotten around to report. Most of the times I can live with what we have now, but other times this REALLY bothers me since there is no way of getting a curve perfectly smooth. Pretty please do something about it :)

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