Layer Parenting and Null Objects

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Layer parenting creates a parent-child relationship between layers where the parent layer influences the position, rotation, and scale of the child. Null objects are invisible layers that work well with parenting! They can be used with parenting to give another layer of control to your animations. This article will teach you how to use the both of these in your projects in Alight Motion.



How to Parent Layers

In a project with at least two layers, tap on the layer you want to be the child layer, then tap the Layer Parent button.



Step 1: Tap the Layer Parenting Icon


From the menu that drops down, select the layer you want to be the parent. Note that the layer you have selected on the timeline is unavailable in the parenting menu, because a layer cannot be parented to itself.



Step 2: Select the parent layer



The parent of the child layer is indicated by the arrow.


 If you want to unparent a child layer you’ve already parented, select “none” from this menu.


How to Use Parenting

When you change the position of a parent, the child moves in tandem. When you rotate the parent, the child rotates around the axis of the parent layer. When you change the parent’s scale, the child grows or shrinks in proportion.

These changes still take effect regardless of whether the child overlaps with the parent or is at a distance.

It’s important to note that the parenting relationship is one-way. Moving, rotating, or scaling the child will have no influence on the parent.  

Layer order on the timeline has no effect on parent relationships.


Parenting Hierarchies

Each layer can at most have one parent, but a parent can have an unlimited number of children. 

A layer with children can also in turn have a parent, allowing layers to be chained together to perform sophisticated animations.



In this project, layers are parented together in a chain to create a sophisticated crane animation.


Effects and Parenting

Effects on a parent layer that change the layer’s position, rotation, and scale also affect children, as do selected warp effects. Effects with this behavior have the Layer Parenting tag in the Effect Browser, and include effects such as Bend, Oscillate, Auto Shake, and Swing.




When the Move Along Path effect is added to a child layer, it will cause the child to move along the outline of the parent. This is useful with Vector Drawing to create curved paths for layers to follow.


The Parenting Helper Effect

The Parenting Helper effect adjusts the behavior of child layers when the parent’s rotation or scale is changed, allowing certain components of the parent’s transformation to be selectively ignored, reduced, or exaggerated. For example, if you want a layer to move as the parent rotates, but without changing its own angle, like gondolas on a ferris wheel, you would use this effect.

This effect allows you to change the mode for Rotation and Scale individually. Each one has there possible options:

  • The “Normal” setting is for default parenting behavior. 
  • The “Locked” setting will prevent the child from rotating or changing size, although its position will change in tandem with the parent.
  • The “Weighted” setting allows degrees of change based on the parent. For example, a weighted rotation of 200% will cause the child to rotate twice as much as the parent. Use the appropriate Rotation Weight or Scale Weight spinner for the adjustment.

Here is an example where we've rotated the parent layer by 45 degrees.



Normal: The child rotates with the parent, around the parent's pivot point.



Locked: The position of the child changes with the rotation of the parent, but the child itself does not rotate.



Weighted: The position of the child changes with the rotation of the parent, and the child rotates depending on the weighting value. At 200%, the child rotates twice the amount of the parent.


There is also an “Auto Rotate” option which will automatically apply rotation to the layer based on the horizontal or vertical movement of the parent layer. This is useful for automatically animating wheels, for example. 

If the wheel doesn’t completely fill the layer, use Radius Adjust to compensate so that the amount of rotation is calculated correctly. For example, if the wheel only fills 70% of the layer, and the outside 30% is transparent, set Radius Adjust to -30.


What are Null Objects?

Null objects are invisible layers, but they can be controlled and animated like any other layer. To add a null object on iPhone and Android, tap Add Layer, then go to Object and tap Null. 




On iPad, go to the Object tab, and then tap Null.




You will see a wireframe indicating the position, scale, and angle of the null object for your reference while editing but this will not appear when you export and share the video.



How to Use Null Objects

Null objects can be used as parents of other layers. This can be useful in a few situations.

When you'd like to have more control over a layer’s animation by using different keyframe timings for separate axes, you can parent that layer to a null object and then animate one axis on the null object itself. This may be useful when you want more control over the position along the Z axis of a camera object, by animating the X and Y position on the camera object itself, and animating Z on the parent null layer. This also works with scale, if you want independent keyframe animation for the X scale and Y scale.

When you want to apply a motion effect uniformly to two or more layers, but also want to be able to animate them separately, you can parent them to a null object and apply the motion effect to the null object. 


Additional Notes

By setting simultaneous position keyframes on a parent layer and child layer, and applying easing to both, you can create a curved motion arc for the child layer.

When you split a parent layer into two halves, the children remain parented to the left half.

The playhead position when you set a layer’s parent can matter. A child layers’ position, rotation, and scale are calculated based on the parent. To avoid a child layer “jumping” when you set a parent, Alight Motion will automatically adjust the child’s position, rotation and scale to compensate at the time you set the parent. Essentially, this means the positional relationship between the child and parent layers is “locked in” when you apply parenting. This means if the parent or child has animation applied, it’s important to scroll the playhead to a position where the layers have the relationship you want before setting up parenting.







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