Improve reordering performance

compose-reordering/src/main/kotlin/it/vfsfitvnm/reordering/AnimatablesPool.kt

@@ -0,0 +1,38 @@
+package it.vfsfitvnm.reordering
+
+import androidx.compose.animation.core.Animatable
+import androidx.compose.animation.core.AnimationVector
+import androidx.compose.animation.core.TwoWayConverter
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
+
+class AnimatablesPool<T, V : AnimationVector>(
+    private val size: Int,
+    private val initialValue: T,
+    typeConverter: TwoWayConverter<T, V>
+) {
+    private val values = MutableList(size) {
+        Animatable(initialValue = initialValue, typeConverter = typeConverter)
+    }
+
+    private val mutex = Mutex()
+
+    init {
+        require(size > 0)
+    }
+
+    suspend fun acquire(): Animatable<T, V> {
+        return mutex.withLock {
+            require(values.isNotEmpty())
+            values.removeFirst()
+        }
+    }
+
+    suspend fun release(animatable: Animatable<T, V>) {
+        mutex.withLock {
+            require(values.size < size)
+            animatable.snapTo(initialValue)
+            values.add(animatable)
+        }
+    }
+}

compose-reordering/src/main/kotlin/it/vfsfitvnm/reordering/DraggedItem.kt

@@ -1,24 +1,34 @@
 package it.vfsfitvnm.reordering
 
+import android.annotation.SuppressLint
 import androidx.compose.foundation.gestures.Orientation
 import androidx.compose.foundation.layout.offset
-import androidx.compose.runtime.getValue
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.composed
 import androidx.compose.ui.unit.IntOffset
 import androidx.compose.ui.zIndex
 
+@SuppressLint("UnnecessaryComposedModifier")
 fun Modifier.draggedItem(
     reorderingState: ReorderingState,
     index: Int
-): Modifier = composed {
-    val translation by reorderingState.translationFor(index)
-
-    offset {
+): Modifier = when (reorderingState.draggingIndex) {
+    -1 -> this
+    index -> offset {
         when (reorderingState.lazyListState.layoutInfo.orientation) {
-            Orientation.Vertical -> IntOffset(0, translation)
-            Orientation.Horizontal -> IntOffset(translation, 0)
+            Orientation.Vertical -> IntOffset(0, reorderingState.offset.value)
+            Orientation.Horizontal -> IntOffset(reorderingState.offset.value, 0)
+        }
+    }.zIndex(1f)
+    else -> offset {
+        val offset =  when (index) {
+            in reorderingState.indexesToAnimate -> reorderingState.indexesToAnimate.getValue(index).value
+            in (reorderingState.draggingIndex + 1)..reorderingState.reachedIndex -> -reorderingState.draggingItemSize
+            in reorderingState.reachedIndex until reorderingState.draggingIndex -> reorderingState.draggingItemSize
+            else -> 0
+        }
+        when (reorderingState.lazyListState.layoutInfo.orientation) {
+            Orientation.Vertical -> IntOffset(0, offset)
+            Orientation.Horizontal -> IntOffset(offset, 0)
         }
     }
-    .zIndex(if (reorderingState.draggingIndex == index) 1f else 0f)
 }

compose-reordering/src/main/kotlin/it/vfsfitvnm/reordering/ReorderingState.kt

@@ -5,14 +5,13 @@ package it.vfsfitvnm.reordering
 import androidx.compose.animation.core.Animatable
 import androidx.compose.animation.core.AnimationVector1D
 import androidx.compose.animation.core.VectorConverter
-import androidx.compose.animation.core.animateIntAsState
 import androidx.compose.foundation.gestures.Orientation
 import androidx.compose.foundation.lazy.LazyListBeyondBoundsInfo
 import androidx.compose.foundation.lazy.LazyListItemInfo
 import androidx.compose.foundation.lazy.LazyListState
 import androidx.compose.runtime.Composable
-import androidx.compose.runtime.State
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateMapOf
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
@@ -35,35 +34,21 @@ class ReorderingState(
 ) {
     private lateinit var lazyListBeyondBoundsInfoInterval: LazyListBeyondBoundsInfo.Interval
     internal val lazyListBeyondBoundsInfo = LazyListBeyondBoundsInfo()
-    internal val offset: Animatable<Int, AnimationVector1D> = Animatable(0, Int.VectorConverter)
+    internal val offset = Animatable(0, Int.VectorConverter)
 
     internal var draggingIndex by mutableStateOf(-1)
-    private var reachedIndex by mutableStateOf(-1)
-    private var draggingItemSize by mutableStateOf(0)
+    internal var reachedIndex by mutableStateOf(-1)
+    internal var draggingItemSize by mutableStateOf(0)
 
     lateinit var itemInfo: LazyListItemInfo
 
-    var previousItemSize = 0
-    var nextItemSize = 0
+    private var previousItemSize = 0
+    private var nextItemSize = 0
 
     private var overscrolled = 0
 
-    private val noTranslation = object : State<Int> {
-        override val value = 0
-    }
-
-    @Composable
-    internal fun translationFor(index: Int): State<Int> = when (draggingIndex) {
-        -1 -> noTranslation
-        index -> offset.asState()
-        else -> animateIntAsState(
-            when (index) {
-                in (draggingIndex + 1)..reachedIndex -> -draggingItemSize
-                in reachedIndex until draggingIndex -> draggingItemSize
-                else -> 0
-            }
-        )
-    }
+    internal var indexesToAnimate = mutableStateMapOf<Int, Animatable<Int, AnimationVector1D>>()
+    private var animatablesPool: AnimatablesPool<Int, AnimationVector1D>? = null
 
     fun onDragStart(index: Int) {
         overscrolled = 0
@@ -85,6 +70,11 @@ class ReorderingState(
 
         lazyListBeyondBoundsInfoInterval =
             lazyListBeyondBoundsInfo.addInterval(index + extraItemCount, index + extraItemCount)
+
+        val size =
+            lazyListState.layoutInfo.viewportEndOffset - lazyListState.layoutInfo.viewportStartOffset
+
+        animatablesPool = AnimatablesPool(size / draggingItemSize + 2, 0, Int.VectorConverter)
     }
 
     fun onDrag(change: PointerInputChange, dragAmount: Offset) {
@@ -106,12 +96,49 @@ class ReorderingState(
                 reachedIndex += 1
                 nextItemSize += draggingItemSize
                 previousItemSize += draggingItemSize
+
+                val indexToAnimate = reachedIndex - if (draggingIndex < reachedIndex) 0 else 1
+
+                coroutineScope.launch {
+                    val animatable = indexesToAnimate.getOrPut(indexToAnimate) {
+                        animatablesPool?.acquire() ?: return@launch
+                    }
+
+                    if (draggingIndex < reachedIndex) {
+                        animatable.snapTo(0)
+                        animatable.animateTo(-draggingItemSize)
+                    } else {
+                        animatable.snapTo(draggingItemSize)
+                        animatable.animateTo(0)
+                    }
+
+                    indexesToAnimate.remove(indexToAnimate)
+                    animatablesPool?.release(animatable)
+                }
             }
         } else if (targetOffset < previousItemSize) {
             if (reachedIndex > 0) {
                 reachedIndex -= 1
                 previousItemSize -= draggingItemSize
                 nextItemSize -= draggingItemSize
+
+                val indexToAnimate = reachedIndex + if (draggingIndex > reachedIndex) 0 else 1
+
+                coroutineScope.launch {
+                    val animatable = indexesToAnimate.getOrPut(indexToAnimate) {
+                        animatablesPool?.acquire() ?: return@launch
+                    }
+
+                    if (draggingIndex > reachedIndex) {
+                        animatable.snapTo(0)
+                        animatable.animateTo(draggingItemSize)
+                    } else {
+                        animatable.snapTo(-draggingItemSize)
+                        animatable.animateTo(0)
+                    }
+                    indexesToAnimate.remove(indexToAnimate)
+                    animatablesPool?.release(animatable)
+                }
             }
         } else {
             val offsetInViewPort = targetOffset + itemInfo.offset - overscrolled
@@ -146,6 +173,7 @@ class ReorderingState(
             }
 
             lazyListBeyondBoundsInfo.removeInterval(lazyListBeyondBoundsInfoInterval)
+            animatablesPool = null
         }
     }