Advanced animations with expressions

When using the keyframe editor you may notice a checkbox called Is expression. If you enable this checkbox you will turn the keyframe into an expression, allowing you to use custom logic to animate your layer.

Once enabled, the editor will show a Edit expression button which will open the code editor. Expressions generally support moth basic functions such as Math.round, Math.ceil, etc.. and a few custom variables are also available (more on these below by example). One thing to keep in mind is functions and other complex control logic is not supported. An error will be shown if the expression can not be processed before saving.

Rotating a layer by time

You can use the provided time variable to access the current time information (in ms). For example, if you wanted to rotate a layer along with the time you could simply write, time. If you wanted to rotate the layer at half the time you could write time * 0.5 or time / 2

Rotating a layer by general progress

Another option is to use the progress variable to animate your layer. This will be a value between 0 and 1 and will already have easing applied (based on the easing of your keyframe). So to rotate your layer a full 360 degrees by the end of the keyframe you could write 360 * progress

Accessing other layers

The most powerful functionality of expressions is the ability to reference other layers in your animation using the layer function. A simple example would be to move layer B at twice the speed of layer A. This could be achieved as follows (assuming layer A already has an animation applied):

layer(Layers['id:Layer A']).property('x') * 2

Notice the Layers object, this is a map of all the available layers. No worries though, IntelliSense will help you find the right layer by it's name.