Migrate DecayAnimation to Kotlin

packages/react-native/ReactAndroid/api/ReactAndroid.api

@@ -439,6 +439,23 @@ public abstract interface class com/facebook/react/ViewManagerOnDemandReactPacka
 	public abstract fun getViewManagerNames (Lcom/facebook/react/bridge/ReactApplicationContext;)Ljava/util/Collection;
 }
 
+public abstract class com/facebook/react/animated/AnimatedNode {
+	public static final field Companion Lcom/facebook/react/animated/AnimatedNode$Companion;
+	public static final field DEFAULT_ANIMATED_NODE_CHILD_COUNT I
+	public static final field INITIAL_BFS_COLOR I
+	public fun <init> ()V
+	public final fun addChild (Lcom/facebook/react/animated/AnimatedNode;)V
+	public fun onAttachedToNode (Lcom/facebook/react/animated/AnimatedNode;)V
+	public fun onDetachedFromNode (Lcom/facebook/react/animated/AnimatedNode;)V
+	public abstract fun prettyPrint ()Ljava/lang/String;
+	public final fun prettyPrintWithChildren ()Ljava/lang/String;
+	public final fun removeChild (Lcom/facebook/react/animated/AnimatedNode;)V
+	public fun update ()V
+}
+
+public final class com/facebook/react/animated/AnimatedNode$Companion {
+}
+
 public class com/facebook/react/animated/NativeAnimatedModule : com/facebook/fbreact/specs/NativeAnimatedModuleSpec, com/facebook/react/bridge/LifecycleEventListener, com/facebook/react/bridge/UIManagerListener {
 	public static final field ANIMATED_MODULE_DEBUG Z
 	public fun <init> (Lcom/facebook/react/bridge/ReactApplicationContext;)V

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/animated/AdditionAnimatedNode.java

@@ -32,11 +32,11 @@ public AdditionAnimatedNode(
 
   @Override
   public void update() {
-    mValue = 0;
+    nodeValue = 0;
     for (int i = 0; i < mInputNodes.length; i++) {
       AnimatedNode animatedNode = mNativeAnimatedNodesManager.getNodeById(mInputNodes[i]);
       if (animatedNode != null && animatedNode instanceof ValueAnimatedNode) {
-        mValue += ((ValueAnimatedNode) animatedNode).getValue();
+        nodeValue += ((ValueAnimatedNode) animatedNode).getValue();
       } else {
         throw new JSApplicationCausedNativeException(
             "Illegal node ID set as an input for Animated.Add node");
@@ -47,7 +47,7 @@ public void update() {
   @Override
   public String prettyPrint() {
     return "AdditionAnimatedNode["
-        + mTag
+        + tag
         + "]: input nodes: "
         + (mInputNodes != null ? mInputNodes.toString() : "null")
         + " - super: "

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/animated/AnimatedNode.kt

@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.animated
+
+import java.util.ArrayList
+
+/** Base class for all Animated.js library node types that can be created on the "native" side. */
+public abstract class AnimatedNode {
+
+  public companion object {
+    public const val INITIAL_BFS_COLOR: Int = 0
+    public const val DEFAULT_ANIMATED_NODE_CHILD_COUNT: Int = 1
+  }
+
+  // TODO: T196787278 Reduce the visibility of these fields to package once we have
+  // converted the whole module to Kotlin
+
+  @JvmField
+  internal var children: MutableList<AnimatedNode>? =
+      null /* lazy-initialized when a child is added */
+  @JvmField internal var activeIncomingNodes: Int = 0
+  @JvmField internal var BFSColor: Int = INITIAL_BFS_COLOR
+  @JvmField internal var tag: Int = -1
+
+  public fun addChild(child: AnimatedNode): Unit {
+    val currentChildren =
+        children
+            ?: ArrayList<AnimatedNode>(DEFAULT_ANIMATED_NODE_CHILD_COUNT).also { children = it }
+
+    currentChildren.add(child)
+    child.onAttachedToNode(this)
+  }
+
+  public fun removeChild(child: AnimatedNode): Unit {
+    val currentChildren = children ?: return
+    child.onDetachedFromNode(this)
+    currentChildren.remove(child)
+  }
+
+  /**
+   * Subclasses may want to override this method in order to store a reference to the parent of a
+   * given node that can then be used to calculate current node's value in {@link #update}. In that
+   * case it is important to also override {@link #onDetachedFromNode} to clear that reference once
+   * current node gets detached.
+   */
+  public open fun onAttachedToNode(parent: AnimatedNode): Unit = Unit
+
+  /** See {@link #onAttachedToNode} */
+  public open fun onDetachedFromNode(parent: AnimatedNode): Unit = Unit
+
+  /**
+   * This method will be run on each node at most once every repetition of the animation loop. It
+   * will be executed on a node only when all the node's parent has already been updated. Therefore
+   * it can be used to calculate node's value.
+   */
+  public open fun update(): Unit = Unit
+
+  /**
+   * Pretty-printer for the AnimatedNode. Only called in production pre-crash for debug diagnostics.
+   */
+  public abstract fun prettyPrint(): String
+
+  public fun prettyPrintWithChildren(): String {
+
+    val currentChildren = children?.joinToString(" ")
+    return prettyPrint() +
+        if (!currentChildren.isNullOrBlank()) " children: $currentChildren" else ""
+  }
+}

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/animated/ColorAnimatedNode.java

@@ -66,7 +66,7 @@ public void onUpdateConfig(ReadableMap config) {
   @Override
   public String prettyPrint() {
     return "ColorAnimatedNode["
-        + mTag
+        + tag
         + "]: r: "
         + mRNodeId
         + " g: "
@@ -94,10 +94,10 @@ private void tryApplyNativeColor() {
     ValueAnimatedNode bNode = (ValueAnimatedNode) mNativeAnimatedNodesManager.getNodeById(mBNodeId);
     ValueAnimatedNode aNode = (ValueAnimatedNode) mNativeAnimatedNodesManager.getNodeById(mANodeId);
 
-    rNode.mValue = Color.red(color);
-    gNode.mValue = Color.green(color);
-    bNode.mValue = Color.blue(color);
-    aNode.mValue = Color.alpha(color) / 255.0;
+    rNode.nodeValue = Color.red(color);
+    gNode.nodeValue = Color.green(color);
+    bNode.nodeValue = Color.blue(color);
+    aNode.nodeValue = Color.alpha(color) / 255.0;
 
     mNativeColorApplied = true;
   }
@@ -116,8 +116,8 @@ private Context getContext() {
   private static Context getContextHelper(AnimatedNode node) {
     // Search children depth-first until we get to a PropsAnimatedNode, from which we can
     // get the view and its context
-    if (node.mChildren != null) {
-      for (AnimatedNode child : node.mChildren) {
+    if (node.children != null) {
+      for (AnimatedNode child : node.children) {
         if (child instanceof PropsAnimatedNode) {
           View view = ((PropsAnimatedNode) child).getConnectedView();
           return view != null ? view.getContext() : null;

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/animated/DecayAnimation.kt

@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.animated
+
+import com.facebook.react.bridge.ReadableMap
+import kotlin.math.abs
+import kotlin.math.exp
+
+/**
+ * Implementation of [AnimationDriver] providing support for decay animations. The implementation is
+ * copied from the JS version in `AnimatedImplementation.js`.
+ */
+internal class DecayAnimation(config: ReadableMap) : AnimationDriver() {
+  private var velocity: Double = 0.0
+  private var deceleration: Double = 0.0
+  private var startFrameTimeMillis: Long = -1
+  private var fromValue: Double = 0.0
+  private var lastValue: Double = 0.0
+  private var iterations: Int = 1
+  private var currentLoop: Int = 1
+
+  init {
+    resetConfig(config)
+  }
+
+  public override fun resetConfig(config: ReadableMap): Unit {
+    velocity = config.getDouble("velocity")
+    deceleration = config.getDouble("deceleration")
+    startFrameTimeMillis = -1
+    fromValue = 0.0
+    lastValue = 0.0
+    iterations = if (config.hasKey("iterations")) config.getInt("iterations") else 1
+    currentLoop = 1
+    mHasFinished = iterations == 0
+  }
+
+  public override fun runAnimationStep(frameTimeNanos: Long) {
+    val frameTimeMillis = frameTimeNanos / 1000000
+    if (startFrameTimeMillis == -1L) {
+      // since this is the first animation step, consider the start to be on the previous frame
+      startFrameTimeMillis = frameTimeMillis - 16
+      if (fromValue == lastValue) { // first iteration, assign mFromValue based on mAnimatedValue
+        fromValue = mAnimatedValue.nodeValue
+      } else { // not the first iteration, reset mAnimatedValue based on mFromValue
+        mAnimatedValue.nodeValue = fromValue
+      }
+      lastValue = mAnimatedValue.nodeValue
+    }
+    val value =
+        (fromValue +
+            velocity / (1 - deceleration) *
+                (1 - exp(-(1 - deceleration) * (frameTimeMillis - startFrameTimeMillis))))
+    if (abs(lastValue - value) < 0.1) {
+      if (iterations == -1 || currentLoop < iterations) { // looping animation, return to start
+        // set mStartFrameTimeMillis to -1 to reset instance variables on the next runAnimationStep
+        startFrameTimeMillis = -1
+        currentLoop++
+      } else { // animation has completed
+        mHasFinished = true
+        return
+      }
+    }
+    lastValue = value
+    mAnimatedValue.nodeValue = value
+  }
+}