Drivers on bone custom properties can get update delays
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In a specific useful circumstance, drivers on the custom properties of bones can create the infamous single-frame delay.

This bug occurs when you have 3 or more bones, which we'll call A, B, and C.

A property (custom or not) on bone A is driven by a custom property on bone B. Then that custom property is driven by another custom property on bone C. Thus, indirectly, the custom property on bone C affects bone A. When changing or animating the custom property on bone C, an update delay is introduced between it and the corresponding property on bone A.

A file is attached that illustrates this in the simplest case.

Because the dependencies are only between bones, which Blender can otherwise handle fine (e.g. with constraints), and is not within a single bone, it seems like this ought to be something that Blender can handle. It is useful to be able to do this when trying to construct multiple complex drivers that share some components, and which you would like to maintain in the future.

If this isn't something that can be fixed under the current depgraph, suggestions on how to work around this limitation are welcome.

Ton Roosendaal (ton) added a comment.Via Old WorldOct 19 2012, 6:50 PM

Hey Nathan!

I'm back to Blender :) first cleaning the tracker, do some finger exercises with bugfixng, but the depsgraph is definitely on the agenda now.
The issue has been extensively noted in the todo for wiki though. Will add your report, and close this for future reference.

Ton Roosendaal (ton) closed this task as "Archived".Via Old WorldOct 19 2012, 6:50 PM

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