Im animating my sine curve indefinetly horizontal...

# compose

[Adriano Celentano]

Im animating my sine curve indefinetly horizontaly, any better ideas how to do it ?

LaunchedEffect(key1 = Unit, block = {
    while (isActive) {
        delay(50)
        horizontalAnimation.value = horizontalAnimation.value + 2.dp
    }
})

Screen Recording 2021-02-21 at 10.47.58.mov

[Adriano Celentano]

i animate the amplitude like this

val transition = rememberInfiniteTransition()
val amplitudeAnimation = transition.animateFloat(
    initialValue = -1f, targetValue = 1f, animationSpec = InfiniteRepeatableSpec(
        tween(3000),
        repeatMode = RepeatMode.Reverse
    )
)

[Adam Powell]

withFrame[Nanos|Millis] { frameTime -> is a better alternative than delay, then you can calculate the amount to animate by based on how much time elapsed since the previous frame. delay will be janky and not align with frames.

[Adam Powell]

@Doris Liu would probably give some more idiomatic advice for the higher level animation system

[jim]

Is there ever a time when delay is the right function in a launched effect? Maybe it should be a warning or something?

[Adam Powell]

It depends on whether you're delaying for animation or for some other pulse. The false positives might be worse than the benefits

[jim]

Just curious, maybe I'm not awake enough yet on a Sunday morning, but why would you delay if not for (1) an animation or (2) sideways data loading which is an terrible practice that should be warned against anyway.

[Doris Liu]

withFrame[Nanos|Millis] makes total sense here for calculating the offset, as you probably want a constant velocity. One thing to watch out for is the rounding error, as compounding rounding error on each frame may produce a subtle drift. Alternatively, an equally viable option would be to have an animation in a while-loop to take care of that calculation/rounding for you. It could be something like:

LaunchedEffect(...) {
        val horizontalAnimation = AnimationState(Dp.VectorConverter, 0.dp)
        while(isActive) {
            horizontalAnimation.animateTo(
                horizontalAnimation.value + 2.dp,
                tween(50, easing = LinearEasing),
                sequentialAnimation = true
            ) {
                // Update something with the animation value
            }
        }
    }

[Doris Liu]

Re delay : if you want to do something once per interval, and the interval is long enough (say 5 seconds) that being off by one frame (from not aligning with frame time) is not a concern. Seems like delay would be a convenient way to achieve that.

[jim]

But why would you want to do that? And shouldn't you be subscribed to a clock at that point, rather than using delay? Otherwise, you are not going to behave correctly when someone accelerates time (eg. unit test) and a variety of other circumstances where the delay approach is fragile.

[Doris Liu]

Accelerating time in unit-tests shouldn't be a problem for delay, assuming you use the TestCoroutineDispatcher or implement DelayController correctly: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-test/kotlinx.coroutines.test/-delay-controller/advance-time-by.html

[Adriano Celentano]

thx for all the valuable info. this slack channel is awesome 🙏