Follow Path constraint works only on curves with Cyclic U option activated #76009

New Issue

Maurizio Memoli · 2020-04-22T22:33:22+02:00

Maurizio Memoli commented

2020-04-22 22:33:22 +02:00

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 441.20

Blender Version
Broken: version: 2.82 (sub 7), branch: master, commit date: 2020-02-12 16:20, hash: blender/blender@77d23b0bd7
Worked: (optional)

Short description of error
If the constraint is not set on fixed position the constrained object will stay at the start position even if the offset is on a different value.
The constraint will work fine if the curve is set to Cyclic U.
This may not be considered a bug, but the "Fixed position" option isn't really working as the name describes.
It is merely remapping the frames value to a range that goes from 0.0 to 1.0. This will cause a slide of the constrained object on the curve when the curve moves and it will not keep its parametric coordinates, it will just keep the position on the percentage of the length of the curve.

Exact steps for others to reproduce the error
For Cyclic U:
Create a Nurbs Curve
Create an Empty
Add a follow path constraint
Set the offset value to 50
in the curve option tab, under Active spline activate Cyclic U

Fixed position:
A simple way to recreate the issue is to create a curve with 6 control points, place the constrained object between the first and second control point and move the sixth control point. You will notice the constrained object moving even if the curve is not actually deforming in that area.

**System Information** Operating system: Windows-10-10.0.18362-SP0 64 Bits Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 441.20 **Blender Version** Broken: version: 2.82 (sub 7), branch: master, commit date: 2020-02-12 16:20, hash: `blender/blender@77d23b0bd7` Worked: (optional) **Short description of error** If the constraint is not set on fixed position the constrained object will stay at the start position even if the offset is on a different value. The constraint will work fine if the curve is set to Cyclic U. This may not be considered a bug, but the "Fixed position" option isn't really working as the name describes. It is merely remapping the frames value to a range that goes from 0.0 to 1.0. This will cause a slide of the constrained object on the curve when the curve moves and it will not keep its parametric coordinates, it will just keep the position on the percentage of the length of the curve. **Exact steps for others to reproduce the error** For Cyclic U: Create a Nurbs Curve Create an Empty Add a follow path constraint Set the offset value to 50 in the curve option tab, under Active spline activate Cyclic U Fixed position: A simple way to recreate the issue is to create a curve with 6 control points, place the constrained object between the first and second control point and move the sixth control point. You will notice the constrained object moving even if the curve is not actually deforming in that area.

Maurizio Memoli commented

2020-04-22 22:33:22 +02:00

Added subscriber: @maumemoli

Germano Cavalcante commented

2020-04-23 16:37:26 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2020-04-23 16:37:26 +02:00

Could you provide a simple file showing the problem?

Richard Antalik commented

2020-04-23 18:47:54 +02:00

Added subscriber: @iss

Richard Antalik commented

2020-04-23 18:47:54 +02:00

Changed status from 'Needs Triage' to: 'Archived'

Richard Antalik closed this issue

2020-04-23 18:47:54 +02:00

Richard Antalik self-assigned this 2020-04-23 18:47:54 +02:00

Richard Antalik commented

2020-04-23 18:47:54 +02:00

Please reffer to documentation before reporting: https://docs.blender.org/manual/en/dev/animation/constraints/relationship/follow_path.html

In first issue I would agree though that wording is quite bad, but it is correct still. Tooltip is also quite misleading.

####Offset
The number of frames to offset from the “animation” defined by the path (by default, from frame 1).

At frame 1 you are at beginning of the curve. If you offset animation by +50 frames empty will correctly start moving from frame 51.

Regarding second issue, descriprion is quite clear. Tooltip seems to be fine as well.

####Fixed Position
Object will stay locked to a single point somewhere along the length of the curve regardless of time.

I will close this report, because I can't see bug in actual behavior, and tag projects, so they can update description of property if they see this as something worth fixing

Please reffer to documentation before reporting: https://docs.blender.org/manual/en/dev/animation/constraints/relationship/follow_path.html In first issue I would agree though that wording is quite bad, but it is correct still. Tooltip is also quite misleading. > ####Offset > The number of frames to offset from the “animation” defined by the path (by default, from frame 1). At frame 1 you are at beginning of the curve. If you offset animation by +50 frames empty will correctly start moving from frame 51. Regarding second issue, descriprion is quite clear. Tooltip seems to be fine as well. > ####Fixed Position > Object will stay locked to a single point somewhere along the length of the curve **regardless of time**. I will close this report, because I can't see bug in actual behavior, and tag projects, so they can update description of property if they see this as something worth fixing

Ryan Inch commented

2020-04-23 21:53:04 +02:00

Added subscriber: @Imaginer

Ryan Inch commented

2020-04-23 21:53:04 +02:00

Offset:
I can confirm that when the curve's Cyclic U property is active the animation starts immediately from frame 1 as opposed to what's set in offset.
@iss This looks like a bug to me.

Fixed Position:
As far as I can tell this is working properly. The "Fixed Position" is defined by percentage, so it makes sense that the object changes position when the curve is edited (for example, made longer).

Offset: I can confirm that when the curve's Cyclic U property is active the animation starts immediately from frame 1 as opposed to what's set in offset. @iss This looks like a bug to me. Fixed Position: As far as I can tell this is working properly. The "Fixed Position" is defined by percentage, so it makes sense that the object changes position when the curve is edited (for example, made longer).

Richard Antalik commented

2020-04-23 22:38:18 +02:00

In #76009#916414, @Imaginer wrote:
Offset:
I can confirm that when the curve's Cyclic U property is active the animation starts immediately from frame 1 as opposed to what's set in offset.
@iss This looks like a bug to me.

Sorry I must have misread report. In any case that is still not a bug IMO, because when curve is cyclic, motion paths will go from -infinity to +infinity.
Therefore offset is now really just "phase shift".

> In #76009#916414, @Imaginer wrote: > Offset: > I can confirm that when the curve's Cyclic U property is active the animation starts immediately from frame 1 as opposed to what's set in offset. > @iss This looks like a bug to me. Sorry I must have misread report. In any case that is still not a bug IMO, because when curve is cyclic, motion paths will go from -infinity to +infinity. Therefore offset is now really just "phase shift".

Maurizio Memoli commented

2020-04-23 23:08:10 +02:00

@iss
I should have gone through the documentation. Sorry for the rush bug report.
But still isn't the change of behavior still when the curve turns Cyclic considered a bug?
It would make more sense having the evaluation time parameter in the constraint itself instead of the curve.

I know this is not the place to make suggestions to improve the software, but having objects sliding on the curve and not having the option to keep them locked on the parameter it is kind of crippling for the rigging workflow.

@iss I should have gone through the documentation. Sorry for the rush bug report. But still isn't the change of behavior still when the curve turns Cyclic considered a bug? It would make more sense having the evaluation time parameter in the constraint itself instead of the curve. I know this is not the place to make suggestions to improve the software, but having objects sliding on the curve and not having the option to keep them locked on the parameter it is kind of crippling for the rigging workflow.

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Follow Path constraint works only on curves with Cyclic U option activated #76009