The interactive performance improvements in After Effects CC include significant enhancements to how expressions are evaluated. Expressions are now evaluated on the render thread, meaning the user interface no longer slows down while an expression is calculating. Cache markings affected by an expression, for example, are updated instead of waiting for the expression to complete. Some expression-heavy compositions render faster due to expanded use of the internal expression cache Faster rendering occurs especially when one expression is dependent on the results of other expressions.
What is more visible as you work is that when an expression fails to evaluate:
- Expression errors appear in a warning banner at the bottom of the Composition and Layer panels instead of in a dialog box.
- The expression is not automatically disabled and continues to evaluate.
The warning banner displays as long as the expression fails to evaluate; that is, until the expression is either fixed or manually disabled.
When you have multiple expressions that fail, you no longer need to click through all the error dialog boxes that appear. Also, when you fix the cause of an expression’s failure (including simply undoing the change), you no longer have to click to re-enable it.
Previously, changing a single property or deleting a single layer could cause hundreds of related expressions to fail. These changes provide some relief to the fingers of expression-heavy users.
Here’s an example of what the expression error warning banner looks like:
On the right side of the expression error warning banner are control buttons:
- The left or right arrow buttons display the previous or next expression error when multiple expressions fail to evaluate.
- The Reveal Expression (magnifying glass) button exposes the property with the failing expression in the Timeline panel. If the expression is in a different composition, that composition opens.
- The Expand/Collapse Warning (up/down arrows) button shows or hides the error text.
The expression error text is one line only, and is clipped to the width of the Composition panel. To see the full expression error text in the old-style dialog box, click the yellow error triangle icon next to the expression in the Timeline panel.
You can hide the entire warning banner if you find it distracting.
Choose Edit > Preferences > General (Windows) or After Effects CC > Preferences > General (Mac OS), and then disable Show Warning Banner When Project Contains Expressions Errors.
When this option is disabled, the warning banner remains hidden even when new expression errors occur. Re-enable this option to view expression errors.
Let us know what you think about the changes to expression evaluation on the After Effects forum.