Bone IK constraint - add lockable axis properties for stretching #83911

New Issue

Daniel Bystedt · 2020-12-17T23:16:22+01:00

Daniel Bystedt commented

2020-12-17 23:16:22 +01:00

Adding task after e-mail conversation with Sybren 2020-12-17

The bone IK constraint can activate stretching on the constrained bones if constrained bones has

Properties / Bone properties / Inverse Kinematics / IK Stretch > 0

example:

bpy.context.object.pose.bones["Bone.005"].ik_stretch = 0.01

The problem is that the constrained bones stretch in all axes and not only in the +Y axis of the bone, which results in unwanted "scaling" of each bone.

Here is a video showing the issue:

ik stretch.mp4

My suggestion is to fix this by adding properties to each bone that show the resulting IK stretching per axis on each bone. These properties should be readable (for drivers) but not possible for the user to change, since the stretching is generated. The property should be lockable by the user in order to fix any unwanted scaling on a specific axis.

Another solution is to add properties that is a factor (multiplier) to the scaling/stretching per axis. The upside is that the user can change the values, but the downside is that the user does not have a property to read the generated IK stretch values.

I leave it up to you to decide what is the most "blender way" in regards to implementation.

*Adding task after e-mail conversation with Sybren 2020-12-17* The bone IK constraint can activate stretching on the constrained bones if constrained bones has **Properties / Bone properties / Inverse Kinematics / IK Stretch > 0** example: ``` bpy.context.object.pose.bones["Bone.005"].ik_stretch = 0.01 ``` The problem is that the constrained bones stretch in all axes and not only in the +Y axis of the bone, which results in unwanted "scaling" of each bone. --- Here is a video showing the issue: [ik stretch.mp4](https://archive.blender.org/developer/F9515707/ik_stretch.mp4) --- My suggestion is to fix this by adding properties to each bone that show the resulting IK stretching per axis on each bone. These properties should be readable (for drivers) but not possible for the user to change, since the stretching is generated. The property should be lockable by the user in order to fix any unwanted scaling on a specific axis. Another solution is to add properties that is a factor (multiplier) to the scaling/stretching per axis. The upside is that the user can change the values, but the downside is that the user does not have a property to read the generated IK stretch values. I leave it up to you to decide what is the most "blender way" in regards to implementation. ![image.png](https://archive.blender.org/developer/F9515708/image.png)

Sybren A. Stüvel was assigned by Daniel Bystedt

2020-12-17 23:16:22 +01:00

Daniel Bystedt commented

2020-12-17 23:16:22 +01:00

Added subscriber: @DanielBystedt

Juan Pablo Bouza commented

2020-12-17 23:22:22 +01:00

Added subscriber: @jpbouza-4

Juan Pablo Bouza commented

2020-12-17 23:22:22 +01:00

I'm gonna take the liberty to add Campbell and Daniel Lara to the conversation because I think both worked on this topic in the past, but I don't remember what solution they got to...

Juan Pablo Bouza commented

2020-12-17 23:24:09 +01:00

OK, as I don't own this task, I don't think I can add subscribers??? haha, you guys do it if you can.

Philipp Oeser commented

2020-12-18 10:42:02 +01:00

Added subscribers: @ideasman42, @pepe-school-land

Sybren A. Stüvel commented

2020-12-18 13:48:48 +01:00

Added subscriber: @brecht

Sybren A. Stüvel commented

2020-12-18 13:48:48 +01:00

I think this is a nice idea. I haven't seen the "read-only but lockable to the current value" approach anywhere else in Blender, but I think it makes sense here.

Adding @brecht as he's the main developer for the constraints (wiki).

I think this is a nice idea. I haven't seen the "read-only but lockable to the current value" approach anywhere else in Blender, but I think it makes sense here. Adding @brecht as he's the main developer for the constraints ([wiki](https://wiki.blender.org/wiki/Modules#Animation_.26_Rigging)).

Sybren A. Stüvel commented

2020-12-18 13:48:57 +01:00

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

Brecht Van Lommel commented

2020-12-18 17:10:36 +01:00

For reading the values: all IK stretch does is modify the bone scale. Reading the bone Y scale through a driver appears to work here. Is that enough?
For control: a single slider to set for how much IK stretch affects both X and Z axis seems most convenient to me. Changing it for Y does not make much sense as the IK chain would not hit the target. Independent control of X and Z seems unimportant.

* For reading the values: all IK stretch does is modify the bone scale. Reading the bone Y scale through a driver appears to work here. Is that enough? * For control: a single slider to set for how much IK stretch affects both X and Z axis seems most convenient to me. Changing it for Y does not make much sense as the IK chain would not hit the target. Independent control of X and Z seems unimportant.

Daniel Bystedt commented

2020-12-18 19:51:45 +01:00

In #83911#1078308, @brecht wrote:

For reading the values: all IK stretch does is modify the bone scale. Reading the bone Y scale through a driver appears to work here. Is that enough?

Yes, that makes sense.

For control: a single slider to set for how much IK stretch affects both X and Z axis seems most convenient to me. Changing it for Y does not make much sense as the IK chain would not hit the target. Independent control of X and Z seems unimportant.

That sounds like a nice solution.

> In #83911#1078308, @brecht wrote: > * For reading the values: all IK stretch does is modify the bone scale. Reading the bone Y scale through a driver appears to work here. Is that enough? Yes, that makes sense. > * For control: a single slider to set for how much IK stretch affects both X and Z axis seems most convenient to me. Changing it for Y does not make much sense as the IK chain would not hit the target. Independent control of X and Z seems unimportant. That sounds like a nice solution.

Sybren A. Stüvel removed their assignment 2021-02-08 10:43:21 +01:00

Sybren A. Stüvel commented

2021-02-08 10:43:21 +01:00

Added subscriber: @dr.sybren

Sybren A. Stüvel commented

2021-02-08 10:43:21 +01:00

As I'm currently working on another project, I don't want to keep claiming this task. I'll unassign this from myself, so that someone else could pick it up.

Philipp Oeser removed the

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Bone IK constraint - add lockable axis properties for stretching #83911