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Inheriting scale from new parent is inconsistent

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Steve Bentley
Inheriting scale from new parent is inconsistent
on Aug 4, 2018 at 6:34:50 am

Ok, am I too tired? Here's a simplified file to demonstrate what's happening. If you make layer 3 a child of layer 2, layer 3's rotation suddenly changes. But (if you undo all of that) if you make layer 2 a child of layer 1 there are no changes in layer 1.
What is it about layer 2 that has an effect on layers that are made children of it. This also works in other combinations but no layer changes when made a child of layer 1 (even if layer 1 is pushed down in the layer order)

I've made a bunch of layers that I now want to control with a super parent, ideally with a cascade where each of the layers is a child of the one before until you get to the last layer being the only direct child of the super parent. Normally if you don't have any keyframes yet, the layers just connect and take on any changes that the new parent object is transformed by but only AFTER the connection is made. The child normally doesn't change simply by connecting it to a new parent who's parameters aren't set to default. In other words, by connecting a child to a parent the child simply zero's out to a new origin through the hierarchy but doesn't usually move or scale or rotate.

In the real project I also tried bringing in a new null and just connecting all the layers to it - some of the children changed at connection time, some didn't, so it seems to be an issue with the child not the parent (since they all have the same parent here). What makes some of these children troublemakers?



12607_inheritancescaleproject.aep.zip



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Kalleheikki Kannisto
Re: Inheriting scale from new parent is inconsistent
on Aug 4, 2018 at 7:32:49 am

After some experimentation, the issue seems to be that if x and z scales of the parent are different from each other, you get an incorrect scale result in the child, if they are the same, you get the expected result of no visual change. I believe you've stumbled upon a bug in the scale calculation of 3D layers' inheritance.

Kalleheikki Kannisto
Senior Graphic Designer


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Steve Bentley
Re: Inheriting scale from new parent is inconsistent
on Aug 4, 2018 at 5:39:25 pm

Thanks K. That sounds like they are using a sort of 2D scale calculation for inheritance (y'know, without the Z).
I'm so used being able to parent to add a slight change to an already stellar motion path of the child without disturbing the child in AE that I knew something was up, and because it stands out against C4D's version where the parent must be either at frame 0 or at the origin, otherwise the PRS of the new parent and the child combine to fling the child somewhere off screen.



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Steve Bentley
Re: Inheriting scale from new parent is inconsistent
on Aug 4, 2018 at 10:00:41 pm

Thanks again for that insight K. I was able to change all my Z scales (which truly don't matter on flat planes) to maatch the X values, and linked all my children in a cascade which resulted in no scale or rotation changes.
You've saved the day again!



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Kalleheikki Kannisto
Re: Inheriting scale from new parent is inconsistent
on Aug 5, 2018 at 12:48:02 pm

[Steve Bentley] " That sounds like they are using a sort of 2D scale calculation for inheritance (y'know, without the Z)."

Sounds likely. Could be the source of many an inexplicable issue with parenting 3D layers. Probably rare enough a problem so that it hasn't reached a bug status. I rarely scale anything differently along the z axis in AE, but I can imagine this could wreak havoc if you actually needed to do so for some reason.

Glad you got it sorted from there.

Kalleheikki Kannisto
Senior Graphic Designer


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Michael Szalapski
Re: Inheriting scale from new parent is inconsistent
on Aug 6, 2018 at 3:49:33 pm

[Kalleheikki Kannisto] "I rarely scale anything differently along the z axis in AE, but I can imagine this could wreak havoc if you actually needed to do so for some reason."

I actually have! So, if you have a bunch of layers all at different levels in z space and you parent them to a null, you can scale that null and it effectively just spreads everything out in z-space. It's really handy for some things. :)

- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')

No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.


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Kalleheikki Kannisto
Re: Inheriting scale from new parent is inconsistent
on Aug 7, 2018 at 6:25:27 am

Yes, true, it's good for temporary things like that, but permanent connections to a scaled parent... imagine leaving the layers connected that way and then having to rotate one of the child layers. If you have scaled the parent on z axis only, you get a differently shaped child at different angles. It will look more stretched the more it is aligned to the z-axis of the parent. Hard to think of a situation where that is desirable behavior.

Kalleheikki Kannisto
Senior Graphic Designer


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