ScreenTransitions.kt

package com.github.terrakok.modo.animation

import androidx.compose.animation.AnimatedContent
import androidx.compose.animation.AnimatedContentTransitionScope
import androidx.compose.animation.AnimatedVisibilityScope
import androidx.compose.animation.ContentTransform
import androidx.compose.animation.core.tween
import androidx.compose.animation.core.updateTransition
import androidx.compose.animation.fadeIn
import androidx.compose.animation.fadeOut
import androidx.compose.animation.scaleIn
import androidx.compose.animation.togetherWith
import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.mutableStateMapOf
import androidx.compose.ui.Modifier
import com.github.terrakok.modo.ComposeRendererScope
import com.github.terrakok.modo.LocalTransitionCompleteChannel
import com.github.terrakok.modo.SaveableContent
import com.github.terrakok.modo.Screen

val displayingScreens = mutableStateMapOf<Screen, Unit>()

typealias ScreenTransitionContent = @Composable AnimatedVisibilityScope.(Screen) -> Unit

/**
 * The way to animate [Screen]'s changing (transition).
 */
@Suppress("MagicNumber")
@Composable
fun ComposeRendererScope<*>.ScreenTransition(
    modifier: Modifier = Modifier,
    screenModifier: Modifier = Modifier,
    transitionSpec: AnimatedContentTransitionScope<Screen>.() -> ContentTransform = {
        fadeIn(animationSpec = tween(220, delayMillis = 90)) +
            scaleIn(initialScale = 0.92f, animationSpec = tween(220, delayMillis = 90)) togetherWith
            fadeOut(animationSpec = tween(90))
    },
    content: ScreenTransitionContent = { it.SaveableContent(screenModifier) }
) {
    val transition = updateTransition(targetState = screen, label = "ScreenTransition")
    transition.AnimatedContent(
        transitionSpec = transitionSpec,
        modifier = modifier,
        contentKey = { it.screenKey },
        content = content
    )
    if (transition.currentState == transition.targetState) {
        val channel = LocalTransitionCompleteChannel.current
        LaunchedEffect(Unit) {
            channel.trySend(Unit)
        }
    }
}