What it does
An expression is a short formula that computes a property's value each frame — wiggle(2, 30), time * 90, loopOut("cycle"), linear(time, 0, 1, 0, 100), thisComp.layer("Null 1").transform.position. Brio uses the After Effects expression language; an expression copied from AE either runs, or fails with a message naming the line and the reason.
In Brio an expression is an Expression modifier in a layer's modifier stack.
How it behaves
- AE units. Expressions read and write position in top-left, Y-down comp pixels; scale and opacity in percent; rotation in degrees clockwise.
- Deterministic. Every value depends only on time, the scene and a per-property seed, so
random()andwiggle()give the same numbers in preview and export, and after a reload. - Errors never break the render. The property keeps the value it had before the expression, and the Properties panel shows the message.
- Expressions can read each other. Reading a property that has its own expression evaluates that one first. A loop (A reads B reads A) uses the pre-expression value, and both show an error.
- No JavaScript engine. No loops (
for,while,do), no user functions (function,return), nonew,thisorclass, no++/--. The last line's value is the result. - Maximum length 64 KB.