Marquee4.kt

LaunchedEffect(textLayoutInfoState.value) {
    // textLayoutInfoState is only calculated if the text overflows
    // its parent, if it doesn't, there's no need for the animation
    val textLayoutInfo = textLayoutInfoState.value ?: return@LaunchedEffect
    if (textLayoutInfo.textWidth <= textLayoutInfo.containerWidth) return@LaunchedEffect

    // 7500 * 200 / 100 = 15s -- 2x container width
    // 7500 * 500 / 250 = 15s -- 2x container width
    // 7500 * 300 / 100 = 22.5s -- 3x container width
    // 7500 * 110 / 100 = 8.25s -- 1.1x container width
    // 7500 * 100 / 200 -- 1/2 container width, doesn't happen because of the if statement above
    // the animation will always take at least 7.5s
    val duration = 7500 * textLayoutInfo.textWidth / textLayoutInfo.containerWidth
    // before the animation starts there's this delay, it's also taken
    // into consideration between cycles
    val delay = 1000L

    do {
        // simple animation that goes from 0 to negative text width,
	// causes the text to scroll left because it's negative
        val animation = TargetBasedAnimation(
            animationSpec = infiniteRepeatable(
                animation = tween(
                    durationMillis = duration,
                    delayMillis = 1000,
                    easing = LinearEasing
                ),
                repeatMode = RepeatMode.Restart
            ),
            typeConverter = Int.VectorConverter,
            initialValue = 0,
            targetValue = -textLayoutInfo.textWidth
        )

        // suspended function that is invoked when a new frame will be drawn
        // returns the frame time in nanos
        val startTime = withFrameNanos { it }

	// this block will keep executing until the animation ends but given that
	// the animation is `infiniteRepeatable` it never ends.
        do {
            // given that `withFrameNanos` is suspendable and runs only once
	    // per frame we don't need to worry about drawing too many times
            val playTime = withFrameNanos { it } - startTime
            offset = (animation.getValueFromNanos(playTime))
        } while (!animation.isFinishedFromNanos(playTime))
	// this code never runs
        delay(delay)
    } while (true)
}