Improve screen transitions

compose-routing/src/main/kotlin/it/vfsfitvnm/route/RouteHandler.kt

@@ -21,7 +21,13 @@ fun RouteHandler(
     modifier: Modifier = Modifier,
     listenToGlobalEmitter: Boolean = false,
     handleBackPress: Boolean = true,
-    transitionSpec: AnimatedContentScope<RouteHandlerScope>.() -> ContentTransform = { fastFade },
+    transitionSpec: AnimatedContentScope<RouteHandlerScope>.() -> ContentTransform = {
+        when {
+            isStacking -> defaultStacking
+            isStill -> defaultStill
+            else -> defaultUnstacking
+        }
+    },
     content: @Composable RouteHandlerScope.() -> Unit
 ) {
     var route by rememberSaveable(stateSaver = Route.Saver) {
@@ -47,7 +53,13 @@ fun RouteHandler(
     modifier: Modifier = Modifier,
     listenToGlobalEmitter: Boolean = false,
     handleBackPress: Boolean = true,
-    transitionSpec: AnimatedContentScope<RouteHandlerScope>.() -> ContentTransform = { fastFade },
+    transitionSpec: AnimatedContentScope<RouteHandlerScope>.() -> ContentTransform = {
+        when {
+            isStacking -> defaultStacking
+            isStill -> defaultStill
+            else -> defaultUnstacking
+        }
+    },
     content: @Composable RouteHandlerScope.() -> Unit
 ) {
     val backDispatcher = LocalOnBackPressedDispatcherOwner.current?.onBackPressedDispatcher

compose-routing/src/main/kotlin/it/vfsfitvnm/route/Transitions.kt

@@ -3,27 +3,44 @@ package it.vfsfitvnm.route
 import androidx.compose.animation.AnimatedContentScope
 import androidx.compose.animation.ContentTransform
 import androidx.compose.animation.EnterTransition
-import androidx.compose.animation.ExitTransition
 import androidx.compose.animation.ExperimentalAnimationApi
-import androidx.compose.animation.core.tween
 import androidx.compose.animation.fadeIn
 import androidx.compose.animation.fadeOut
-import androidx.compose.animation.with
+import androidx.compose.animation.scaleOut
 
 @ExperimentalAnimationApi
-val AnimatedContentScope<RouteHandlerScope>.leftSlide: ContentTransform
-    get() = slideIntoContainer(AnimatedContentScope.SlideDirection.Left) with
-            slideOutOfContainer(AnimatedContentScope.SlideDirection.Left)
+val defaultStacking = ContentTransform(
+    initialContentExit = scaleOut(targetScale = 0.9f) + fadeOut(),
+    targetContentEnter = fadeIn(),
+    targetContentZIndex = 1f
+)
 
 @ExperimentalAnimationApi
-val AnimatedContentScope<RouteHandlerScope>.rightSlide: ContentTransform
-    get() = slideIntoContainer(AnimatedContentScope.SlideDirection.Right) with
-            slideOutOfContainer(AnimatedContentScope.SlideDirection.Right)
+val defaultUnstacking = ContentTransform(
+    initialContentExit = fadeOut(),
+    targetContentEnter = EnterTransition.None,
+    targetContentZIndex = 0f
+)
 
 @ExperimentalAnimationApi
-val AnimatedContentScope<RouteHandlerScope>.fastFade: ContentTransform
-    get() = fadeIn(tween(200)) with fadeOut(tween(200))
+val defaultStill = ContentTransform(
+    initialContentExit = scaleOut(targetScale = 0.9f) + fadeOut(),
+    targetContentEnter = fadeIn(),
+    targetContentZIndex = 1f
+)
 
 @ExperimentalAnimationApi
-val AnimatedContentScope<RouteHandlerScope>.empty: ContentTransform
-    get() = EnterTransition.None with ExitTransition.None
+inline val AnimatedContentScope<RouteHandlerScope>.isStacking: Boolean
+    get() = initialState.route == null && targetState.route != null
+
+@ExperimentalAnimationApi
+inline val AnimatedContentScope<RouteHandlerScope>.isUnstacking: Boolean
+    get() = initialState.route != null && targetState.route == null
+
+@ExperimentalAnimationApi
+inline val AnimatedContentScope<RouteHandlerScope>.isStill: Boolean
+    get() = initialState.route == null && targetState.route == null
+
+@ExperimentalAnimationApi
+inline val AnimatedContentScope<RouteHandlerScope>.isUnknown: Boolean
+    get() = initialState.route != null && targetState.route != null