New to Altia Design 11.3, the Mask object allows you to easily create high-end animations and effects that are cut or conformed to a certain shape using the mask.
NOTE: There is also a long-form article with sample dsn files for creating arc-shaped gauges both with and without the Mask object here:
https://altia.zendesk.com/entries/108008183-Arc-Shaped-Gauges-and-Other-Animated-Reveal-Effects