Jetpack Compose自定义动画与Animatable详解

fun Modifier.animateContentSize(
    animationSpec: FiniteAnimationSpec<IntSize> = spring(),
    finishedListener: ((initialValue: IntSize, targetValue: IntSize) -> Unit)? = null
): Modifier

@Stable
fun <T> spring(
    dampingRatio: Float = Spring.DampingRatioNoBouncy,
    stiffness: Float = Spring.StiffnessMedium,
    visibilityThreshold: T? = null
): SpringSpec<T> = SpringSpec(dampingRatio, stiffness, visibilityThreshold)

@Stable
fun <T> tween(
    durationMillis: Int = DefaultDurationMillis,
    delayMillis: Int = 0,
    easing: Easing = FastOutSlowInEasing
): TweenSpec<T> = TweenSpec(durationMillis, delayMillis, easing)
val FastOutSlowInEasing: Easing = CubicBezierEasing(0.4f, 0.0f, 0.2f, 1.0f)

@Stable
fun <T> keyframes(
    init: KeyframesSpec.KeyframesSpecConfig<T>.() -> Unit
): KeyframesSpec<T> {
    return KeyframesSpec(KeyframesSpec.KeyframesSpecConfig<T>().apply(init))
}

val value by animateFloatAsState(
    targetValue = 1f,
    animationSpec = keyframes {
        durationMillis = 375
        0.0f at 0 with LinearOutSlowInEasing // for 0-15 ms
        0.2f at 15 with FastOutLinearInEasing // for 15-75 ms
        0.4f at 75 // ms
        0.4f at 225 // ms
    }
)

@Stable
fun <T> repeatable(
    iterations: Int,
    animation: DurationBasedAnimationSpec<T>,
    repeatMode: RepeatMode = RepeatMode.Restart,
    initialStartOffset: StartOffset = StartOffset(0)
): RepeatableSpec<T> = RepeatableSpec(iterations, animation, repeatMode, initialStartOffset)

@Stable
fun <T> snap(delayMillis: Int = 0) = SnapSpec<T>(delayMillis)

// Start out gray and animate to green/red based on `ok`
val color = remember { Animatable(Color.Gray) }
LaunchedEffect(ok) {
    color.animateTo(if (ok) Color.Green else Color.Red)
}
Box(Modifier.fillMaxSize().background(color.value))

	Column(modifier = Modifier.fillMaxWidth()) {
        // Creates an `Animatable` to animate Offset and `remember` it.
        val animatedOffset = remember { Animatable(Offset(0f, 0f), Offset.VectorConverter) }
        Box(
            Modifier.fillMaxSize().background(Color(0xffb99aff)).pointerInput(Unit) {
                coroutineScope {
                    while (true) {
                        val offset = awaitPointerEventScope {
                            awaitFirstDown().position
                        }
                        // Launch a new coroutine for animation so the touch detection thread is not
                        // blocked.
                        launch {
                            // Animates to the pressed position, with the given animation spec.
                            animatedOffset.animateTo(
                                offset,
                                animationSpec = spring(stiffness = Spring.StiffnessLow)
                            )
                        }
                    }
                }
            }
        ) {
            Text("Tap anywhere", Modifier.align(Alignment.Center))
            Box(
                Modifier
                    .offset {
                        // Use the animated offset as the offset of the Box.
                        IntOffset(
                            animatedOffset.value.x.roundToInt(),
                            animatedOffset.value.y.roundToInt()
                        )
                    }
                    .size(40.dp)
                    .background(Color(0xff3c1361), CircleShape)
            )
        }
    }