GlitterBox

glitterBox.kt

@Composable
fun GlitterBox(
    rainbow: List<Color> = SkittlesRainbow,
    fleckCount: Int = 2,
    visible: Boolean = true
) {

    var size by remember { mutableStateOf(Size.Zero) }
    var source by remember { mutableStateOf(Offset(200f, 200f)) }
    var glitterState by remember {
        mutableStateOf(
            GlitterState(
                speed = 0.5f,
                colors = rainbow,
                glitterShape = GlitterShape.Mixed,
                fleckCount = fleckCount,
                source = source
            )
        )
    }
    var lastFrame by remember { mutableStateOf(-1L) }
    LaunchedEffect(visible) {
        while (visible && isActive) {
            withFrameMillis { newTick ->
                val elapsedMillis = newTick - lastFrame
                val wasFirstFrame = lastFrame < 0
                lastFrame = newTick
                if (wasFirstFrame) return@withFrameMillis
                glitterState.next(elapsedMillis)
            }
        }
    }
    Box(
        Modifier
            .fillMaxSize()
            .onSizeChanged { size = it.toSize() }
    ) {
        Canvas(
            modifier = Modifier
                .fillMaxSize()
        ) {
            glitterState = glitterState.sizeChanged(this.size)
            if (visible) {
                for (fleck in glitterState.flecks) {
                    fleck.draw(drawContext.canvas)
                }
            }
        }
        Box(
            Modifier
                .offset { source.round() }
                .size(10.dp)
                .background(Color.Magenta)
                .pointerInput(Unit) {
                    detectDragGestures { _, dragAmount ->
                        val summed = source + dragAmount
                        val newValue = Offset(
                            x = summed.x.coerceIn(0f, size.width - 10.dp.toPx()),
                            y = summed.y.coerceIn(0f, size.height - 10.dp.toPx())
                        )
                        source = newValue
                        glitterState = glitterState.updateSource(source)
                    }
                }
        )
    }
}