JavaFX supports animations using the tools in the `javafx.animation` package, but it lacks an easy way of defining animations in stylesheets. This feature has often been requested, but is still missing [0] [1] [2].
While there are several ways to tackle this problem (an alternative notation is presented in [2]), I think the best approach is to implement CSS Transitions [3] for JavaFX. CSS Transitions is an established and stable specification, and it is ubiquitous all over the web. I've prepared a PR that illustrates how that feature can look like in JavaFX: https://github.com/openjdk/jfx/pull/870 With this PR, JavaFX would support animated transitions for all numeric and `Interpolatable` styleable properties. However, in order to support transitions for CSS sub-properties like `-fx-background-color`, several background-related types must be made interpolatable as well (the same is true for border-related types). If this proposal goes forward, I plan to deliver the feature in two installments: 1. CSS Transitions (the above PR) 2. Interpolation support for `Background`, `BackgroundFill`, `CornerRadii`, `Insets`, `Border`, `BorderWidths` and `Margins` I'm looking foward for comments and feedback. [0] https://bugs.openjdk.org/browse/JDK-8283676 [1] https://bugs.openjdk.org/browse/JDK-8092084 [2] https://bugs.openjdk.org/browse/JDK-8090892 [3] https://www.w3.org/TR/css-transitions-1/
