Geometry Nodes: Curve Extract Spline Node
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Authored by Johnny Matthews (guitargeek) on Jul 29 2021, 5:08 PM.

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Hans Goudey (HooglyBoogly)
Jacques Lucke (JacquesLucke)

Summary

This node takes a curve input and a selection (Attribute (bool) or int index). The spline from the input curve with that index chosen (modulus to number of splines for "wrapping") or with a "true" value on the attribute is output to a new curve.

Use cases:

Multiple splines that are interchangeable in a single curve and you want to select one of them or one of them at random.
Animated lightning. Where each spline is a shape of a bolt. then you could keyframe the spline number.
You have a single curve object and you just want to pull out a single part of it
Reordering the splines in a curve without changing the original. Curve => Multiple Spline Extracts => Reordered into a Join Geometry
Pulling out multiple splines from a curve based on an attribute

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Repository: rB Blender

Event Timeline

Johnny Matthews (guitargeek) requested review of this revision.Jul 29 2021, 5:08 PM

Johnny Matthews (guitargeek) created this revision.

Hi @Johnny Matthews (guitargeek) I wonder what's the exact use case you wrote this node for? Isn't it easier to drag and drop curve objects(with one spline in it) into a node tree than blindly trying to set the right spline index?

In D12079#311969, @Miro Horváth (dreamak) wrote:

Hi @Johnny Matthews (guitargeek) I wonder what's the exact use case you wrote this node for? Isn't it easier to drag and drop curve objects(with one spline in it) into a node tree than blindly trying to set the right spline index?

Some ideas:

You have multiple splines that are interchangeable in a single curve and you want to select one of them or one of them at random.
Animated lightning. Where each spline is a shape of a bolt. then you could keyframe the spline number.
Another might be where you have a single curve object and you just want to pull out a single part of it
Reordering the splines in a curve without changing the original. Curve => Multiple Spline Extracts => Reordered into a Join Geometry

Paul Larson (GeorgiaPacific) awarded a token.Jul 29 2021, 10:35 PM

Paul Larson (GeorgiaPacific) added a subscriber: Paul Larson (GeorgiaPacific).

Deen (Bit) awarded a token.Jul 31 2021, 5:02 AM

user1 (user1) added a subscriber: user1 (user1).Jul 31 2021, 3:44 PM

There is some overlap with nodes like point geometry delete, etc. And I'm not totally convinced that an index input makes more sense than a selection attribute input, but generally I think the node is reasonable.

I think I'd remove the "Recenter" feature though. That should be solved more generally with a way to sample a single location from the spline and then a transform node (another thing that would work perfectly with the fields proposal!)

Maybe the use cases could be part of the patch description.

source/blender/nodes/geometry/nodes/node_geo_curve_extract_spline.cc
50	You can use `spline.translate()`

Johnny Matthews (guitargeek) edited the summary of this revision. (Show Details)Aug 2 2021, 9:51 PM

Remove recenter option
Add Attribute Selection
Make format did a number on a couple files

Small RNA fix

Charlie Jolly (charlie) mentioned this in T86749: Geometry Node Community Additions.Aug 10 2021, 2:15 PM

I think we should wait until after the attribute workflow changes are committed to master, so we can see how this fits/whether it is still necessary.

release/scripts/startup/nodeitems_builtins.py
210–255	Unrelated changes
source/blender/makesrna/intern/rna_nodetree.c
9198 ↗	(On Diff #40424)	Even though it's a bit annoying, I think, this should use its own enum, because it's more about choosing whether to use a selection or an index.