swing-ui-animation

The animation engine for Compose Swing UI, and the containers that animate a composable in, out and between states. It provides the familiar Compose animation APIs - animate*AsState, Animatable, updateTransition / Transition, rememberInfiniteTransition, easing curves (including CubicBezierEasing), and the spring / tween / keyframes specs - for the Float, Int, java.awt.Color, and generic (TwoWayConverter) value types.

Usage

Animations run with no extra wiring inside a setContent { ... } composition: they are driven by the window's frame clock automatically, advancing at the display's refresh rate while an animation is in flight and resting otherwise.

import org.jetbrains.compose.swing.animation.core.animateFloatAsState
import androidx.compose.runtime.getValue

val alpha by animateFloatAsState(if (visible) 1f else 0f)

A java.awt.Color animates through animateColorAsState, which interpolates in Oklab and returns an sRGB color. For value types beyond those, supply a TwoWayConverter. The animation APIs are documented in KDoc.

ScrollState.animateScrollTo and animateScrollBy travel a scroll pane to a position over time instead of in one write, holding the pane's position until they arrive.

Animating a composable

AnimatedVisibility runs content through an enter and an exit transition as a boolean flips. AnimatedContent settles on a target state, running the content it leaves out while the content it moves to runs in, and traveling between their sizes. Crossfade fades between the contents of its states and animates no size. SwingModifier.animateContentSize leaves a layout's content alone and animates only the size the content asks for. Transitions combine with +.

AnimatedVisibility(visible = expanded, enter = fadeIn() + expandVertically()) {
    Label(text = "details")
}

AnimatedContent and Crossfade compose each visible state's content separately. Use the state passed to the content lambda to choose what to show, so outgoing content keeps its own state while it leaves. For AnimatedContent, contentKey identifies states that should reuse the same content.

The content is laid out by a Foundation layout, so it takes fillMaxWidth or fillMaxHeight to fill the container. SwingModifier.animateEnterExit gives one part of the content an enter and an exit of its own, on the same transition, so the container waits for it. The part must be Decoratable and under a Foundation layout parent; Box is one example.

Related

• ../README.md - project overview and quick start.

• ../swing-ui/README.md - the core library.