Curve Modifier on polyline #79500

New Issue

shannon zachow · 2020-08-04T08:43:08+02:00

shannon zachow commented

2020-08-04 08:43:08 +02:00

System Information
Operating system: Linux
Graphics card: NVidia

Blender Version
Broken: 2.83.3, 2.91.0a (8356012068, built 2020-08-03)
Worked:

Short description of error
not bugs, but shortcomings -- Curve Modifier logic is treating straight line segments of polyline as linear curve.

Curve Modifier "cuts corner" around polyline corner, depending on Properties > Curve > Preview_Resolution_U = [1,64]
Geometry is differentially sheared along straight line segment. (Treating straight line segments as radial projection.)

Exact steps for others to reproduce the error
see attached file test015_curvedFence.blend

(1.)
Select polyline "FenceLine"
Properties > Curve > Preview_Resolution_U:
set to 1: square fence becomes pentagonal.
set to 64: corner effects mostly invisible.
(why should a straight line segment depend on evaluation resolution?)

(2.)
sheared geometry is most visible in the big FencePosts, but it affects the smaller FencePickets too.
(I understand there is no good answer to the big posts at the corners, but why should the shear effect extend variably along an entire straight line segment?)

Last FencePost (Array End Cap) is offset as reported in #79498.
Pseudo-circular fence included just for comparison. Logic works great for ~circular~ curves. Thanks for Blender!

**System Information** Operating system: Linux Graphics card: NVidia **Blender Version** Broken: 2.83.3, 2.91.0a (8356012068d0, built 2020-08-03) Worked: **Short description of error** not bugs, but shortcomings -- Curve Modifier logic is treating straight line segments of polyline as linear curve. 1. Curve Modifier "cuts corner" around polyline corner, depending on Properties > Curve > Preview_Resolution_U = [1,64] 2. Geometry is differentially sheared along straight line segment. (Treating straight line segments as radial projection.) **Exact steps for others to reproduce the error** see attached file [test015_curvedFence.blend](https://archive.blender.org/developer/F8743678/test015_curvedFence.blend) (1.) Select polyline "FenceLine" Properties > Curve > Preview_Resolution_U: set to 1: square fence becomes pentagonal. set to 64: corner effects mostly invisible. (why should a straight line segment depend on evaluation resolution?) (2.) sheared geometry is most visible in the big FencePosts, but it affects the smaller FencePickets too. (I understand there is no good answer to the big posts *at the corners*, but why should the shear effect extend variably along an entire straight line segment?) Last FencePost (Array End Cap) is offset as reported in #79498. Pseudo-circular fence included just for comparison. Logic works great for ~circular~ curves. Thanks for Blender!

shannon zachow commented

2020-08-04 08:43:08 +02:00

Added subscriber: @shannonz-1

Richard Antalik commented

2020-08-05 04:15:48 +02:00

Added subscribers: @lichtwerk, @iss

Richard Antalik commented

2020-08-05 04:15:48 +02:00

Even if curve is "straight" it is still evaluated as curve.

I was able to mostly eliminate shear by subdividing curves and adjusted control points in corners, but it is not perfect still. I am not sure what would be the solution, but this is not the site to discuss that really. I would suggest to try one of the community websites: https://www.blender.org/community/

Not sure if there is any bug. In manual it is stated that

The resolution property defines the number of points that are computed between every pair of control points.

Which doesn't seem to be consistent unless I am missing something. @lichtwerk do you have some more insight here?

Even if curve is "straight" it is still evaluated as curve. I was able to mostly eliminate shear by subdividing curves and adjusted control points in corners, but it is not perfect still. I am not sure what would be the solution, but this is not the site to discuss that really. I would suggest to try one of the community websites: https://www.blender.org/community/ Not sure if there is any bug. In manual it is stated that >The resolution property defines the number of points that are computed between every pair of control points. Which doesn't seem to be consistent unless I am missing something. @lichtwerk do you have some more insight here?

Campbell Barton commented

2020-08-05 07:21:10 +02:00

Added subscriber: @ideasman42