Circular Carousel with Correct Drag

circular_carousel_07.kt

private fun Modifier.drag(
    state: CircularCarouselState,
) = pointerInput(Unit) {
    val decay = splineBasedDecay<Float>(this)
    coroutineScope {
        while (true) {
            val pointerInput = awaitPointerEventScope { awaitFirstDown() }
            state.stop()
            val tracker = VelocityTracker()
            val degreesPerPixel = 180f / size.width.toFloat()
            awaitPointerEventScope {
                // 1
                val isTopHalf = pointerInput.position.y < size.height / 2f
                // 2
                val signum = when {
                    isTopHalf -> -1f
                    else -> 1f
                }
                horizontalDrag(pointerInput.id) { change ->
                    // 3
                    val horizontalDragOffset = state.angle + signum * change.positionChange().x * degreesPerPixel
                    launch {
                        state.snapTo(horizontalDragOffset)
                    }
                    tracker.addPosition(change.uptimeMillis, change.position)
                    if (change.positionChange() != Offset.Zero) change.consume()
                }
                val velocity = tracker.calculateVelocity().x
                val targetAngle = decay.calculateTargetValue(
                    state.angle,
                    // 4
                    signum * velocity * degreesPerPixel,
                )
                launch {
                    state.decayTo(
                        angle = targetAngle,
                        // 5
                        velocity = signum * velocity * degreesPerPixel,
                    )
                }
            }
        }
    }
}