Add proper gesture when user navigates to or from a conversation.

app/src/main/java/org/thoughtcrime/securesms/window/AppScaffold.kt

@@ -7,6 +7,8 @@ package org.thoughtcrime.securesms.window
 
 import android.content.res.Configuration
 import android.content.res.Resources
+import androidx.compose.animation.EnterTransition
+import androidx.compose.animation.ExitTransition
 import androidx.compose.foundation.background
 import androidx.compose.foundation.interaction.MutableInteractionSource
 import androidx.compose.foundation.layout.Box
@@ -14,6 +16,7 @@ import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.displayCutoutPadding
 import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.offset
 import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material3.LocalMinimumInteractiveComponentSize
@@ -30,9 +33,11 @@ import androidx.compose.material3.adaptive.navigation.NavigableListDetailPaneSca
 import androidx.compose.material3.adaptive.navigation.ThreePaneScaffoldNavigator
 import androidx.compose.material3.adaptive.navigation.rememberListDetailPaneScaffoldNavigator
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.alpha
 import androidx.compose.ui.draw.clipToBounds
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.layout.layout
@@ -42,6 +47,7 @@ import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
+import androidx.compose.ui.zIndex
 import androidx.window.core.ExperimentalWindowCoreApi
 import androidx.window.core.layout.WindowHeightSizeClass
 import androidx.window.core.layout.WindowWidthSizeClass
@@ -228,9 +234,28 @@ fun AppScaffold(
   NavigableListDetailPaneScaffold(
     navigator = navigator,
     listPane = {
-      AnimatedPane {
+      val offset by animateDp(
+        targetWhenHiding = {
+          (-48).dp
+        },
+        targetWhenShowing = {
+          0.dp
+        }
+      )
+
+      val alpha by animateFloat {
+        1f
+      }
+
+      AnimatedPane(
+        enterTransition = EnterTransition.None,
+        exitTransition = ExitTransition.None,
+        modifier = Modifier.zIndex(0f)
+      ) {
         Box(
           modifier = Modifier
+            .alpha(alpha)
+            .offset(x = offset)
             .clipToBounds()
             .layout { measurable, constraints ->
               val width = max(minPaneWidth.roundToPx(), constraints.maxWidth)
@@ -258,9 +283,28 @@ fun AppScaffold(
       }
     },
     detailPane = {
-      AnimatedPane {
+      val offset by animateDp(
+        targetWhenHiding = {
+          48.dp
+        },
+        targetWhenShowing = {
+          0.dp
+        }
+      )
+
+      val alpha by animateFloat {
+        1f
+      }
+
+      AnimatedPane(
+        enterTransition = EnterTransition.None,
+        exitTransition = ExitTransition.None,
+        modifier = Modifier.zIndex(1f)
+      ) {
         Box(
           modifier = Modifier
+            .alpha(alpha)
+            .offset(x = offset)
             .clipToBounds()
             .layout { measurable, constraints ->
               val width = max(minPaneWidth.roundToPx(), constraints.maxWidth)

app/src/main/java/org/thoughtcrime/securesms/window/AppScaffoldAnimators.kt

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2025 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.thoughtcrime.securesms.window
+
+import androidx.compose.animation.core.CubicBezierEasing
+import androidx.compose.animation.core.animateDp
+import androidx.compose.animation.core.animateFloat
+import androidx.compose.animation.core.tween
+import androidx.compose.material3.adaptive.ExperimentalMaterial3AdaptiveApi
+import androidx.compose.material3.adaptive.layout.PaneAdaptedValue
+import androidx.compose.material3.adaptive.layout.ThreePaneScaffoldPaneScope
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.State
+import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.dp
+
+private val easing = CubicBezierEasing(0.4f, 0.0f, 0.2f, 1f)
+
+@OptIn(ExperimentalMaterial3AdaptiveApi::class)
+@Composable
+fun ThreePaneScaffoldPaneScope.animateDp(
+  targetWhenHiding: () -> Dp = { 0.dp },
+  targetWhenShowing: () -> Dp
+): State<Dp> {
+  return scaffoldStateTransition.animateDp(
+    transitionSpec = { tween(durationMillis = 200, easing = easing) }
+  ) {
+    val isHiding = it[paneRole] == PaneAdaptedValue.Hidden
+
+    if (isHiding) {
+      targetWhenHiding()
+    } else {
+      targetWhenShowing()
+    }
+  }
+}
+
+@OptIn(ExperimentalMaterial3AdaptiveApi::class)
+@Composable
+fun ThreePaneScaffoldPaneScope.animateFloat(
+  targetWhenHiding: () -> Float = { 0f },
+  targetWhenShowing: () -> Float
+): State<Float> {
+  return scaffoldStateTransition.animateFloat(
+    transitionSpec = { tween(durationMillis = 200, easing = easing) }
+  ) {
+    val isHiding = it[paneRole] == PaneAdaptedValue.Hidden
+
+    if (isHiding) {
+      targetWhenHiding()
+    } else {
+      targetWhenShowing()
+    }
+  }
+}