changing curve handles type to "vector" makes weird rotations for dupliframes #44393

New Issue

mathieu menuet · 2015-04-14T22:41:19+02:00

mathieu menuet commented

2015-04-14 22:41:19 +02:00

System Information
all

Blender Version
Broken: 2.74

Short description of error
when an object is duplicated with dupliframes onto a curve, changing the handles type in the curve makes a mess on rotations. Giving the handles a translation of 0 resolves the problem.

Exact steps for others to reproduce the error
Open attached blend. The edited curve is the same curve as the one on the left, but with handles type as "vector". Note how the rotation of the dupliframes' object breaks compared to the original curve. Now press G and click without moving the mouse, the rotation are again right.
Awaited behavior: the step with null translation should not be required, the rotation should always follow the curve.
bug_dupliframes_curve_vector.blend

**System Information** all **Blender Version** Broken: 2.74 **Short description of error** when an object is duplicated with dupliframes onto a curve, changing the handles type in the curve makes a mess on rotations. Giving the handles a translation of 0 resolves the problem. **Exact steps for others to reproduce the error** Open attached blend. The edited curve is the same curve as the one on the left, but with handles type as "vector". Note how the rotation of the dupliframes' object breaks compared to the original curve. Now press G and click without moving the mouse, the rotation are again right. Awaited behavior: the step with null translation should not be required, the rotation should always follow the curve. [bug_dupliframes_curve_vector.blend](https://archive.blender.org/developer/F162038/bug_dupliframes_curve_vector.blend)

mathieu menuet commented

2015-04-14 22:41:19 +02:00

Changed status to: 'Open'

mathieu menuet commented

2015-04-14 22:41:19 +02:00

Added subscriber: @bliblubli

Bastien Montagne commented

2015-04-17 08:49:15 +02:00

Added subscriber: @mont29

Bastien Montagne commented

2015-04-17 08:49:15 +02:00

Can confirm the issue…

Bastien Montagne self-assigned this 2015-04-17 10:22:26 +02:00

Bastien Montagne commented

2015-04-17 10:22:26 +02:00

Ok, so far, I understood why fake-translating things fixes the issue - because this switch handles from 'Vector' to 'Free' type.

DevNote: Segments between two vector handles get an optimization in curve handling, since they generate perfect straight lines, no need to subdivide them in 'Resolution U' number of sub-segments. Something is going wrong here, and breaks part of curve path it seems…

Ok, so far, I understood why fake-translating things fixes the issue - because this switch handles from 'Vector' to 'Free' type. DevNote: Segments between two vector handles get an optimization in curve handling, since they generate perfect straight lines, no need to subdivide them in 'Resolution U' number of sub-segments. Something is going wrong here, and breaks part of curve path it seems…

mathieu menuet commented

2015-04-17 11:52:37 +02:00

thank you Bastien, switching to 'free' type solves the problem in the simple case file of the report, sadly for some reason, it doesn't work in the original file where the bug was first triggered. Here is a simple part of the file from original scene: bug_dupliframes_curve_vector_v2.blend . I hope it can help.

thank you Bastien, switching to 'free' type solves the problem in the simple case file of the report, sadly for some reason, it doesn't work in the original file where the bug was first triggered. Here is a simple part of the file from original scene: [bug_dupliframes_curve_vector_v2.blend](https://archive.blender.org/developer/F163472/bug_dupliframes_curve_vector_v2.blend) . I hope it can help.

Bastien Montagne removed their assignment 2015-04-17 13:25:23 +02:00

Sergey Sharybin was assigned by Bastien Montagne

2015-04-17 13:25:23 +02:00

Bastien Montagne commented

2015-04-17 13:25:23 +02:00

Bah… Spent the whole morning on this nightmare… and only good news is, I understand exactly what’s going on: Rotation (orientation) is represented by a quaternion at every BevPoint of the bevel list (the way those quats are generated is rather complex btw), and then when generating curve’s path from that BevelList, each PathPoint gets an interpolattion of its nearest BevPoints' quats.

Now, this is perfect for 'smooth' BevPoints, but not for 'sharp' ones!

Note that this issue is especially visible with vector handles, but actually affects any non-aligned control point (you should get an abrupt rotation in those cases, not a smooth interpolated one).

For 'sharp' points, we'd probably need two quats actually, one for each side. Then, if a BevPoint is tagged as sharp (split_tag), we can use its second quat when on its second 'side', in calc_curvepath… Tried to compute those second quats directly in calc_curvepath, but this seems pretty much impossible (at least for my level of quat knowledge :| ).

Before spending more time on this, Sergey, would love to have your feedback?

Bah… Spent the whole morning on this nightmare… and only good news is, I understand exactly what’s going on: Rotation (orientation) is represented by a quaternion at every BevPoint of the bevel list (the way those quats are generated is rather complex btw), and then when generating curve’s path from that BevelList, each PathPoint gets an interpolattion of its nearest BevPoints' quats. Now, this is perfect for 'smooth' BevPoints, but not for 'sharp' ones! Note that this issue is especially visible with vector handles, but actually affects any non-aligned control point (you should get an abrupt rotation in those cases, not a smooth interpolated one). For 'sharp' points, we'd probably need two quats actually, one for each side. Then, if a BevPoint is tagged as sharp (`split_tag`), we can use its second quat when on its second 'side', in `calc_curvepath`… Tried to compute those second quats directly in `calc_curvepath`, but this seems pretty much impossible (at least for my level of quat knowledge :| ). Before spending more time on this, Sergey, would love to have your feedback?

Sergey Sharybin was unassigned by Bastien Montagne

2015-04-17 13:25:45 +02:00

Bastien Montagne self-assigned this 2015-04-17 13:25:45 +02:00

Bastien Montagne commented

2015-04-17 13:25:45 +02:00

Added subscriber: @Sergey

Bastien Montagne commented

2015-04-17 13:25:45 +02:00

eeek, wanted to CC, not reassign :|

Sergey Sharybin commented

2015-04-17 15:14:24 +02:00

@mont29, not sure what kind of feedback you're expecting here, you pretty much nailed what's happening in there. It's not perfect, but that's how it was intended to be implemented. Improvements are always possible, but IMO it belongs to a bigger project of curves renewal.

Bastien Montagne commented

2015-04-17 15:44:35 +02:00

Changed status from 'Open' to: 'Archived'

Bastien Montagne closed this issue

2015-04-17 15:44:35 +02:00

Bastien Montagne commented

2015-04-17 15:44:35 +02:00

Yeah, wanted more or less that kind of advice. :)

Thought about it a bit more, and there is not only the rotation that is an issue here in 'sharp' points case… Fixing this correctly is beyond scope of bugreport, so closing as TODO for now.

@bliblubli about your other issue, workaround is actually always the same:

do not use vector handles (convert them to free ones).
increase U resolution of the curve until you have enough sub-segments to prevent any artifact.

Yeah, wanted more or less that kind of advice. :) Thought about it a bit more, and there is not only the rotation that is an issue here in 'sharp' points case… Fixing this correctly is beyond scope of bugreport, so closing [as TODO](http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo/Tools#Curves) for now. @bliblubli about your other issue, workaround is actually always the same: * do not use vector handles (convert them to free ones). * increase U resolution of the curve until you have enough sub-segments to prevent any artifact.

mathieu menuet commented

2015-04-17 19:50:55 +02:00

well, I tried on the second file I uploaded here, it doesn't work even with the maximum of 64. Please help.

mathieu menuet commented

2015-05-06 08:36:18 +02:00

The bug also trigger with free handles and with an increased U (64 is max). Please have a look again.

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changing curve handles type to "vector" makes weird rotations for dupliframes #44393