length of the spline does not work after apllying hooks #72025

New Issue

ML · 2019-11-28T20:39:26+01:00

ML commented

2019-11-28 20:39:26 +01:00

System Information
Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce GTX 1050 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 436.30

Blender Version
Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-11-20 14:27, hash: 26bd5ebd42
Worked: (optional)

Short description of error
Let's create any of the splines in blender (nurbs, bezier) and then use know function: bpy.data.curves["NurbsCurve"].splines- [x].calc_length()
It's smoothly working. But after you apply hook modifier and move the empty somewhere, length does not change the value. Thant problem is crucial for custom squash with spline IK.

Exact steps for others to reproduce the error
create spline >[edit mode] > select one of the vertices > ctrl+h > hook to new object > [object mode] > to Python console copy: bpy.data.curves["NurbsCurve"].splines- [x].calc_length() with correct name "NurbsCurve" or "BezierCurve" > a value > move the empty somewhere > again use console with same code > it gives same value even the legth was changed

**System Information** Operating system: Windows-10-10.0.18362 64 Bits Graphics card: GeForce GTX 1050 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 436.30 **Blender Version** Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-11-20 14:27, hash: `26bd5ebd42` Worked: (optional) **Short description of error** Let's create any of the splines in blender (nurbs, bezier) and then use know function: bpy.data.curves["NurbsCurve"].splines- [x].calc_length() It's smoothly working. But after you apply hook modifier and move the empty somewhere, length does not change the value. Thant problem is crucial for custom squash with spline IK. **Exact steps for others to reproduce the error** create spline >[edit mode] > select one of the vertices > ctrl+h > hook to new object > [object mode] > to Python console copy: bpy.data.curves["NurbsCurve"].splines- [x].calc_length() with correct name "NurbsCurve" or "BezierCurve" > a value > move the empty somewhere > again use console with same code > it gives same value even the legth was changed

ML commented

2019-11-28 20:39:26 +01:00

Added subscriber: @MarcelLegindi

blender-admin commented

2019-11-28 20:39:26 +01:00

#81091 was marked as duplicate of this issue

Germano Cavalcante commented

2019-11-29 13:49:08 +01:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2019-11-29 13:49:08 +01:00

Changed status from 'Open' to: 'Archived'

Germano Cavalcante closed this issue

2019-11-29 13:49:08 +01:00

Germano Cavalcante self-assigned this 2019-11-29 13:49:08 +01:00

Germano Cavalcante commented

2019-11-29 13:49:08 +01:00

As we can see in the code, calc_length is executed on the data of the object. That is, with no effect of any modifier.
Different objects can have the same data, so there is no way for the code to know which modified object it should calculate the length of.

Blender 2.8 has a bug with curve modifiers (#71055) changing all objects with the same data. But that will be fixed.

As we can see in the code, `calc_length` is executed on the `data` of the object. That is, with no effect of any modifier. Different objects can have the same `data`, so there is no way for the code to know which modified object it should calculate the length of. Blender 2.8 has a bug with curve modifiers (#71055) changing all objects with the same `data`. But that will be fixed.

ML commented

2019-11-29 22:45:10 +01:00

Well, I don't understand, is it functional or not? When I use hook and move .. the calc_length does not work precise - so I do something wrong? If so, what exactly?

ML commented

2019-12-01 12:31:55 +01:00

there is the proof - this is not working and its a bug. If I understand the usage.

there is the proof - this is not working and its a bug. If I understand the usage. ![zk01.gif](https://archive.blender.org/developer/F8183333/zk01.gif)

Germano Cavalcante commented

2019-12-01 15:49:58 +01:00

To explain further...

We have: object, data and modifier.
Object = data + modifiers
The object is the Curve (NurbsCurve).
The data are the splines of the Curve (the data is confusingly also called NurbsCurve on this object, but the name can be changed in the properties).
The modifier is Hook.

calc_length is a function of the data and not of the object.

We can have more than one object with the same data:
ObjectA = data + modifiersA
ObjectB = data + modifiersB

Objects can have different lengths but the data remains the same.

To explain further... We have: object, data and modifier. Object = data + modifiers The object is the Curve (NurbsCurve). The data are the splines of the Curve (the data is confusingly also called NurbsCurve on this object, but the name can be changed in the properties). The modifier is Hook. `calc_length` is a function of the data and not of the object. We can have more than one object with the same data: ObjectA = data + modifiersA ObjectB = data + modifiersB Objects can have different lengths but the data remains the same.

ML commented

2019-12-01 16:17:55 +01:00

I see, thank you. So is there any option how to measure the spline .. or some other method how to make custom squash besides ratio(spline_length/hooked_spline_length)*scaleY_of_the_bone ? ... you know if you have 15spine bones.. or 2 BBones and scale it properly by distance from the root?

Germano Cavalcante commented

2019-12-01 16:34:58 +01:00

I don't know off the top of my head (you may have to create a temporary mesh as a last resort).

ML commented

2019-12-01 17:50:24 +01:00

Ok thank you very much ..But that's a pity. May I suggest to make it like new function somewhere in this forum? You know, control spline IK properly and fast is crucial for any cartoon character in rigging and trying to measure it by an array modificators is very slow for complex rigs.

Joseph Brandenburg commented

2019-12-02 07:25:09 +01:00

Added subscriber: @Josephbburg

Joseph Brandenburg commented

2019-12-02 07:25:09 +01:00

Is it possible to get an evaluated version of the curve data (not the mesh)?

Anyhow, about a year ago, I made a right-click-select proposal related to this problem. https://blender.community/c/rightclickselect/4ncbbc/ In the meantime, I've come up with a pretty good solution to the measurement problem for my addon, Chain Tools, which I'd be happy to share if you're interested.

When measuring a curve for a rig, especially for squash and stretch, it isn't necessary to get the actual measurements- you only really need to compare the base length to the posed length (for the y-axis scale). Then you can take the reciprocal of this measurement to set the scale for the x and z axes. I usually create a dummy spline IK that is set to space the bones out evenly. I make sure to apply the pose to edit mode a few times to prevent its length from changing when changing into pose mode. Then I can use the y-scale (local space) of any bone in the chain to measure the length of the curve - if the curve starts out at 5 units, and the bone's scale is 1.5, then I know the length of the curve is 5 * 1.5 = 7.5. This is usually good enough for whatever I want to do.

Is it possible to get an evaluated version of the curve data (not the mesh)? Anyhow, about a year ago, I made a right-click-select proposal related to this problem. https://blender.community/c/rightclickselect/4ncbbc/ In the meantime, I've come up with a pretty good solution to the measurement problem for my addon, Chain Tools, which I'd be happy to share if you're interested. When measuring a curve for a rig, especially for squash and stretch, it isn't necessary to get the actual measurements- you only really need to compare the base length to the posed length (for the y-axis scale). Then you can take the reciprocal of this measurement to set the scale for the x and z axes. I usually create a dummy spline IK that is set to space the bones out evenly. I make sure to apply the pose to edit mode a few times to prevent its length from changing when changing into pose mode. Then I can use the y-scale (local space) of any bone in the chain to measure the length of the curve - if the curve starts out at 5 units, and the bone's scale is 1.5, then I know the length of the curve is 5 * 1.5 = 7.5. This is usually good enough for whatever I want to do.

ML commented

2019-12-02 11:06:16 +01:00

Thank you very much, Joseph. So if I understand right, you compare true (start) length of the spline (without modifiers) with IK-spline chain length with scaleY turn on, by basic bone length * its scale after stretching.

I asked in blender.stackexchange if somebody wants more solutions: https://blender.stackexchange.com/questions/159714/custom-squash-and-stretch-without-spline-length-ratio/159719?noredirect=1#comment270625_159719

Thank you very much, Joseph. So if I understand right, you compare true (start) length of the spline (without modifiers) with IK-spline chain length with scaleY turn on, by basic bone length * its scale after stretching. I asked in blender.stackexchange if somebody wants more solutions: https://blender.stackexchange.com/questions/159714/custom-squash-and-stretch-without-spline-length-ratio/159719?noredirect=1#comment270625_159719

Philipp Oeser commented

2020-09-23 15:05:18 +02:00

Added subscribers: @elie, @lichtwerk

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length of the spline does not work after apllying hooks #72025