MediaControlButtons_2.kt

object MediaControlButtons {

    private val HIDDEN = "hidden"
    private val VISIBLE = "visible"

    private val alpha = FloatPropKey()
    private val transitionDef by lazy {
        transitionDefinition {
            state(HIDDEN) {
                this[alpha] = 0f
            }
            state(VISIBLE) {
                this[alpha] = 1f
            }

            transition(fromState = HIDDEN, toState = VISIBLE) {
                alpha using tween(
                        durationMillis = 250,
                        easing = LinearEasing
                )
            }

            transition(fromState = VISIBLE, toState = HIDDEN) {
                alpha using tween(
                        durationMillis = 250,
                        easing = LinearEasing
                )
            }
        }
    }

    @Composable
    operator fun invoke(modifier: Modifier = Modifier) {
        val controller = VideoPlayerControllerAmbient.current

        val controlsEnabled by controller.controlsEnabled.collectAsState()

        // Dictates the direction of appear animation.
        // If controlsVisible is true, appear animation needs to be triggered.
        val controlsVisible by controller.controlsVisible.collectAsState()

        // When controls are not visible anymore we should remove them from UI tree
        // Controls by default should always be on screen.
        // Only when disappear animation finishes, controls can be freely cleared from the tree.
        val (controlsExistOnUITree, setControlsExistOnUITree) = stateFor(controlsVisible) { true }

        val appearTransition = transition(
                transitionDef,
                initState = HIDDEN,
                toState = if(controlsVisible) VISIBLE else HIDDEN,
                onStateChangeFinished = {
                    setControlsExistOnUITree(it == VISIBLE)
                }
        )

        if (controlsEnabled && controlsExistOnUITree) {
            Content(modifier = Modifier
                    .drawOpacity(appearTransition[alpha])
                    .drawBackground(Color.Black.copy(alpha = appearTransition[alpha]*0.6f))
                    + modifier)
        }
    }

    @Composable
    fun Content(modifier: Modifier = Modifier) {
        val controller = VideoPlayerControllerAmbient.current

        Stack(modifier = Modifier + modifier) {

            Box(modifier = Modifier.gravity(Alignment.Center).fillMaxSize().clickable(indication = null) {
                controller.hideControls()
            })
            PositionAndDurationNumbers(modifier = Modifier.gravity(Alignment.BottomCenter))
            PlayPauseButton(modifier = Modifier.gravity(Alignment.Center))
        }
    }
}