A circular reveal effect modifier for Jetpack Compose.

CircularReveal.kt

/**
 * A modifier that clips the composable content using a circular reveal animation. The circle will
 * expand or shrink whenever [isVisible] changes.
 *
 * For more control over the transition, consider using this method's variant which allows passing
 * a [State] object to control the progress of the reveal animation.
 *
 * By default, the circle is centered in the content. However, custom positions can be specified using
 * [revealFrom]. The specified offsets should range from 0 (left/top) to 1 (right/bottom).
 *
 * @param isVisible Determines whether content is visible or not. If true, circle expands; if false, it shrinks.
 * @param revealFrom Custom position from which to start the circular reveal. Default is center of content.
 * @param durationMillis Duration of animation in milliseconds. Default is 250ms.
 * @param easing Easing function used for animation. Default is EaseInOutSine.
 * @param size Size state of component being revealed. Default size is (0, 0).
 */
fun Modifier.circularReveal(
    isVisible: Boolean,
    revealFrom: Offset = Offset(0.5f, 0.5f),
    durationMillis: Int = 250,
    easing: Easing = EaseInOutSine,
    size: MutableState<IntSize> = mutableStateOf(IntSize(0, 0))
): Modifier =
    onGloballyPositioned {
        size.value = it.size
    }.composed(
        factory = {

            val animationProgress: State<Float> = animateFloatAsState(
                targetValue = if (isVisible) 1f else 0f,
                animationSpec = tween(durationMillis = durationMillis, easing = easing),
                label = ""
            )

            circularReveal(animationProgress, revealFrom / size.value.toSize())
        },
        inspectorInfo = debugInspectorInfo {
            name = "circularReveal"
            properties["visible"] = isVisible
            properties["revealFrom"] = revealFrom
            properties["durationMillis"] = durationMillis
        }
    )

/**
 * A modifier that applies a circular reveal animation to the composable content using a transition progress state.
 * The radius of the circle used for clipping will be calculated based on the transition progress.
 *
 * @param transitionProgress The state of progress for the transition. This determines the radius of the circle used for clipping.
 * @param revealFrom The position from which to start the circular reveal. Default is center of content.
 */
private fun Modifier.circularReveal(
    transitionProgress: State<Float>,
    revealFrom: Offset = Offset(0.5f, 0.5f)
): Modifier = drawWithCache {
    val path = Path()

    val center = revealFrom * size
    val radius = calculateRadius(revealFrom, size)

    path.addOval(Rect(center, radius * transitionProgress.value))

    onDrawWithContent {
        clipPath(path) { this@onDrawWithContent.drawContent() }
    }
}

operator fun Offset.times(size: Size): Offset = Offset(x * size.width, y * size.height)

operator fun Offset.div(size: Size): Offset {
    val dx = if (size.width == 0f) x else x / size.width
    val dy = if (size.height == 0f) y else y / size.height
    return Offset(dx, dy)
}

private fun calculateRadius(normalizedOrigin: Offset, size: Size) = with(normalizedOrigin) {
    val x = (if (x > 0.5f) x else 1 - x) * size.width
    val y = (if (y > 0.5f) y else 1 - y) * size.height
    sqrt(x * x + y * y)
}

DraggableCircle.kt

import androidx.compose.foundation.gestures.detectDragGestures
import androidx.compose.foundation.gestures.detectTapGestures
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.offset
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clip
import androidx.compose.ui.geometry.Offset
import androidx.compose.ui.input.pointer.pointerInput
import androidx.compose.ui.layout.onGloballyPositioned
import androidx.compose.ui.layout.positionInRoot
import androidx.compose.ui.unit.IntOffset
import androidx.compose.ui.unit.dp
import kotlin.math.roundToInt

@Composable
fun DraggableCircle(
    modifier: Modifier = Modifier,
    onTap: (Offset) -> Unit
) {
    var offsetX by remember { mutableStateOf(0f) }
    var offsetY by remember { mutableStateOf(0f) }

    val position = remember { mutableStateOf(Offset(0f, 0f)) }

    Box(
        modifier = Modifier
            .offset { IntOffset(offsetX.roundToInt(), offsetY.roundToInt()) }
            .onGloballyPositioned {
                position.value = it.positionInRoot()
            }
            .pointerInput(Unit) {
                detectTapGestures { onTap(it + position.value) }
            }
            .pointerInput(Unit) {
                detectDragGestures { change, dragAmount ->
                    change.consume()
                    offsetX += dragAmount.x
                    offsetY += dragAmount.y
                }
            }
            .clip(RoundedCornerShape(25.dp))
            .then(modifier)
    )
}

RevealTest.kt

import androidx.compose.foundation.background
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.height
import androidx.compose.foundation.layout.size
import androidx.compose.material3.MaterialTheme
import androidx.compose.runtime.Composable
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.geometry.Offset
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp
import de.check24.profis.partner.shared.material3.theme.AppTheme

@Composable
private fun RevealTest() {
    Box(
        modifier = Modifier
            .background(MaterialTheme.colorScheme.surface)
    ) {

        val isVisible = remember { mutableStateOf(false) }
        val revealFrom = remember { mutableStateOf(Offset(0f, 0f)) }

        Box(
            modifier = Modifier
                .background(MaterialTheme.colorScheme.error)
                .fillMaxWidth()
                .height(150.dp)
        )

        Box(
            modifier = Modifier
                .circularReveal(
                    isVisible = isVisible.value,
                    revealFrom = revealFrom.value
                )
                .background(MaterialTheme.colorScheme.primary)
                .fillMaxWidth()
                .height(300.dp)
        ) {

        }

        DraggableCircle(
            modifier = Modifier
                .background(MaterialTheme.colorScheme.tertiary)
                .size(50.dp)
                .align(Alignment.CenterEnd)
        ) {
            revealFrom.value = it
            isVisible.value = !isVisible.value
        }
    }
}

@Preview(showBackground = true)
@Composable
private fun RevealTestPreview() {
    AppTheme {
        RevealTest()
    }
}