GN: Undefined behavior for subdivided cyclical single-point Catmull-Rom splines #102537

New Issue

Mattias Fredriksson · 2022-11-16T00:13:46+01:00

2022-11-16 00:13:46 +01:00

System Information
Operating system: Windows-10-10.0.19045-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 512.15

Blender Version
Broken: version: 3.4.0 Beta, branch: master, commit date: 2022-11-15 01:30, hash: 56f783d883
Worked: Never? broken in 3.3.1 and likely since introduction of the Catmull-Rom type in the 'SetSplineType' node (which is not available in 3.0.0 or 3.2.1).

Short description of error

Cyclical Catmull-Rom splines with only a single control point generates undefined behavior in geometry nodes.

Exact steps for others to reproduce the error

Single point Catmull-Rom splines can easily generated using 'SetSplineType' on cyclical single point splines created by either:

a) Through 'SetSplineCyclic' node on a single point spline.
b) By deleting controlpoints from a cyclic spline until only one remains.

Presumably there are many ways to generate undefined behavior for cyclic splines with a single controlpoint (not only for Catmull-Rom type as it is fairly easy to trigger BLI_asserts in debug mode). A simple way to do so is to use the subdivision node on Catmull-Rom splines (see below).

Reference file

cyclic_single_point_bug_report.blend

Plausible solutions

Limit the possibility to create cyclical splines (i.e. 'SetSplineCyclic' should not enable the cyclic property on the node).
Always treat single point splines as an edge case in geometry nodes (which would ignore the cyclic property).
Profit?

**System Information** Operating system: Windows-10-10.0.19045-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 2070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 512.15 **Blender Version** Broken: version: 3.4.0 Beta, branch: master, commit date: 2022-11-15 01:30, hash: `56f783d883` Worked: Never? broken in 3.3.1 and likely since introduction of the Catmull-Rom type in the 'SetSplineType' node (which is not available in 3.0.0 or 3.2.1). **Short description of error** Cyclical Catmull-Rom splines with only a single control point generates undefined behavior in geometry nodes. **Exact steps for others to reproduce the error** Single point Catmull-Rom splines can easily generated using 'SetSplineType' on cyclical single point splines created by either: a) Through 'SetSplineCyclic' node on a single point spline. b) By deleting controlpoints from a cyclic spline until only one remains. Presumably there are many ways to generate undefined behavior for cyclic splines with a single controlpoint (not only for Catmull-Rom type as it is fairly easy to trigger BLI_asserts in debug mode). A simple way to do so is to use the subdivision node on Catmull-Rom splines (see below). ![SinglePointCatmullUndefined.gif](https://archive.blender.org/developer/F13919860/SinglePointCatmullUndefined.gif) **Reference file** [cyclic_single_point_bug_report.blend](https://archive.blender.org/developer/F13919865/cyclic_single_point_bug_report.blend) **Plausible solutions** - Limit the possibility to create cyclical splines (i.e. 'SetSplineCyclic' should not enable the cyclic property on the node). - Always treat single point splines as an edge case in geometry nodes (which would ignore the cyclic property). - Profit?

Mattias Fredriksson commented

2022-11-16 00:13:46 +01:00

Added subscriber: @Osares