Build the scroll event payload in one JNI call

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ScrollEvent.kt

@@ -10,10 +10,8 @@ package com.facebook.react.views.scroll
 import android.os.SystemClock
 import androidx.core.util.Pools.SynchronizedPool
 import com.facebook.infer.annotation.Assertions
-import com.facebook.react.bridge.Arguments
 import com.facebook.react.bridge.ReactSoftExceptionLogger
 import com.facebook.react.bridge.WritableMap
-import com.facebook.react.bridge.buildReadableMap
 import com.facebook.react.internal.featureflags.ReactNativeFeatureFlags
 import com.facebook.react.uimanager.PixelUtil.toDIPFromPixel
 import com.facebook.react.uimanager.common.ViewUtil
@@ -76,46 +74,24 @@ public class ScrollEvent private constructor() : Event<ScrollEvent>() {
   override fun canCoalesce(): Boolean = scrollEventType == ScrollEventType.SCROLL
 
   override fun getEventData(): WritableMap {
-    val contentInset = buildReadableMap {
-      put("top", 0.0)
-      put("bottom", 0.0)
-      put("left", 0.0)
-      put("right", 0.0)
-    }
-
-    val contentOffset = buildReadableMap {
-      put("x", toDIPFromPixel(scrollX).toDouble())
-      put("y", toDIPFromPixel(scrollY).toDouble())
-    }
-
-    val contentSize = buildReadableMap {
-      put("width", toDIPFromPixel(contentWidth.toFloat()).toDouble())
-      put("height", toDIPFromPixel(contentHeight.toFloat()).toDouble())
-    }
-
-    val layoutMeasurement = buildReadableMap {
-      put("width", toDIPFromPixel(scrollViewWidth.toFloat()).toDouble())
-      put("height", toDIPFromPixel(scrollViewHeight.toFloat()).toDouble())
-    }
-
-    val velocity = buildReadableMap {
-      put("x", toDIPFromPixel(xVelocity).toDouble())
-      put("y", toDIPFromPixel(yVelocity).toDouble())
-    }
-
-    val event = Arguments.createMap()
-    event.putMap("contentInset", contentInset)
-    event.putMap("contentOffset", contentOffset)
-    event.putMap("contentSize", contentSize)
-    event.putMap("layoutMeasurement", layoutMeasurement)
-    event.putMap("velocity", velocity)
-    event.putInt("target", viewTag)
-    event.putDouble("timestamp", timestamp.toDouble())
-    event.putBoolean(
-        "responderIgnoreScroll",
+    val data = DoubleArray(ScrollEventHelper.FIELDS)
+    data[ScrollEventHelper.CONTENT_OFFSET_X_INDEX] = toDIPFromPixel(scrollX).toDouble()
+    data[ScrollEventHelper.CONTENT_OFFSET_Y_INDEX] = toDIPFromPixel(scrollY).toDouble()
+    data[ScrollEventHelper.CONTENT_WIDTH_INDEX] = toDIPFromPixel(contentWidth.toFloat()).toDouble()
+    data[ScrollEventHelper.CONTENT_HEIGHT_INDEX] =
+        toDIPFromPixel(contentHeight.toFloat()).toDouble()
+    data[ScrollEventHelper.LAYOUT_WIDTH_INDEX] =
+        toDIPFromPixel(scrollViewWidth.toFloat()).toDouble()
+    data[ScrollEventHelper.LAYOUT_HEIGHT_INDEX] =
+        toDIPFromPixel(scrollViewHeight.toFloat()).toDouble()
+    data[ScrollEventHelper.VELOCITY_X_INDEX] = toDIPFromPixel(xVelocity).toDouble()
+    data[ScrollEventHelper.VELOCITY_Y_INDEX] = toDIPFromPixel(yVelocity).toDouble()
+    data[ScrollEventHelper.TIMESTAMP_INDEX] = timestamp.toDouble()
+    return ScrollEventHelper.nativeCreateScrollPayload(
+        data,
+        viewTag,
         !ReactNativeFeatureFlags.shouldTriggerResponderTransferOnScrollAndroid(),
     )
-    return event
   }
 
   public companion object {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ScrollEventHelper.kt

@@ -0,0 +1,47 @@
+/*
+ * 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.views.scroll
+
+import com.facebook.proguard.annotations.DoNotStrip
+import com.facebook.react.bridge.ReactNativeJNISoLoader
+import com.facebook.react.bridge.WritableNativeMap
+
+/** Builds the payload of a [ScrollEvent] in one native call. */
+@DoNotStrip
+internal object ScrollEventHelper {
+  init {
+    ReactNativeJNISoLoader.staticInit()
+  }
+
+  // Keep in sync with the field indices in ScrollEventHelper.cpp.
+  const val CONTENT_OFFSET_X_INDEX = 0
+  const val CONTENT_OFFSET_Y_INDEX = 1
+  const val CONTENT_WIDTH_INDEX = 2
+  const val CONTENT_HEIGHT_INDEX = 3
+  const val LAYOUT_WIDTH_INDEX = 4
+  const val LAYOUT_HEIGHT_INDEX = 5
+  const val VELOCITY_X_INDEX = 6
+  const val VELOCITY_Y_INDEX = 7
+  const val TIMESTAMP_INDEX = 8
+  const val FIELDS = 9
+
+  /**
+   * Creates the payload of a scroll event: `contentInset` (all zero), `contentOffset`,
+   * `contentSize`, `layoutMeasurement`, `velocity`, `target`, `timestamp` and
+   * `responderIgnoreScroll`.
+   *
+   * @param data [FIELDS] values, in DIPs, at the indices above.
+   */
+  @DoNotStrip
+  @JvmStatic
+  external fun nativeCreateScrollPayload(
+      data: DoubleArray,
+      target: Int,
+      responderIgnoreScroll: Boolean,
+  ): WritableNativeMap
+}

packages/react-native/ReactAndroid/src/main/jni/react/jni/CMakeLists.txt

@@ -32,6 +32,7 @@ add_library(
           OnLoad-common.cpp
           ReadableNativeArray.cpp
           ReadableNativeMap.cpp
+          ScrollEventHelper.cpp
           TouchesHelper.cpp
           TransformHelper.cpp
           WritableNativeArray.cpp

packages/react-native/ReactAndroid/src/main/jni/react/jni/OnLoad.cpp

@@ -11,6 +11,7 @@
 #include <fbjni/fbjni.h>
 
 #include "InspectorNetworkRequestListener.h"
+#include "ScrollEventHelper.h"
 #include "TouchesHelper.h"
 #include "TransformHelper.h"
 
@@ -35,6 +36,7 @@ extern "C" JNIEXPORT jint JNI_OnLoad(JavaVM* vm, void* reserved) {
     FLAGS_minloglevel = 0;
 #endif
     InspectorNetworkRequestListener::registerNatives();
+    ScrollEventHelper::registerNatives();
     TouchesHelper::registerNatives();
     TransformHelper::registerNatives();
   });

packages/react-native/ReactAndroid/src/main/jni/react/jni/ScrollEventHelper.cpp

@@ -0,0 +1,81 @@
+/*
+ * 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.
+ */
+
+#include "ScrollEventHelper.h"
+
+#include <stdexcept>
+
+#include "WritableNativeMap.h"
+
+using namespace facebook::jni;
+
+namespace facebook::react {
+
+namespace {
+
+// Keep in sync with the field indices in ScrollEventHelper.kt.
+constexpr jint kContentOffsetXIndex = 0;
+constexpr jint kContentOffsetYIndex = 1;
+constexpr jint kContentWidthIndex = 2;
+constexpr jint kContentHeightIndex = 3;
+constexpr jint kLayoutWidthIndex = 4;
+constexpr jint kLayoutHeightIndex = 5;
+constexpr jint kVelocityXIndex = 6;
+constexpr jint kVelocityYIndex = 7;
+constexpr jint kTimestampIndex = 8;
+constexpr jint kFields = 9;
+
+local_ref<WritableNativeMap::jhybridobject> createScrollPayload(
+    alias_ref<jclass> /*unused*/,
+    alias_ref<JArrayDouble> data,
+    jint target,
+    jboolean responderIgnoreScroll) {
+  if (data->size() != kFields) {
+    throw std::invalid_argument("Invalid scroll event data");
+  }
+  auto values = data->getRegion(0, kFields);
+  const double* fields = values.get();
+
+  auto jPayload = WritableNativeMap::newObjectJavaArgs();
+  auto* payload = jPayload->cthis();
+  // NOLINTBEGIN(cppcoreguidelines-pro-bounds-pointer-arithmetic)
+  WritableNativeMap contentInset(
+      folly::dynamic::object("top", 0.0)("bottom", 0.0)("left", 0.0)(
+          "right", 0.0));
+  payload->putNativeMap("contentInset", &contentInset);
+  WritableNativeMap contentOffset(
+      folly::dynamic::object("x", fields[kContentOffsetXIndex])(
+          "y", fields[kContentOffsetYIndex]));
+  payload->putNativeMap("contentOffset", &contentOffset);
+  WritableNativeMap contentSize(
+      folly::dynamic::object("width", fields[kContentWidthIndex])(
+          "height", fields[kContentHeightIndex]));
+  payload->putNativeMap("contentSize", &contentSize);
+  WritableNativeMap layoutMeasurement(
+      folly::dynamic::object("width", fields[kLayoutWidthIndex])(
+          "height", fields[kLayoutHeightIndex]));
+  payload->putNativeMap("layoutMeasurement", &layoutMeasurement);
+  WritableNativeMap velocity(
+      folly::dynamic::object("x", fields[kVelocityXIndex])(
+          "y", fields[kVelocityYIndex]));
+  payload->putNativeMap("velocity", &velocity);
+  payload->putInt("target", target);
+  payload->putDouble("timestamp", fields[kTimestampIndex]);
+  // NOLINTEND(cppcoreguidelines-pro-bounds-pointer-arithmetic)
+  payload->putBoolean("responderIgnoreScroll", responderIgnoreScroll != 0u);
+  return jPayload;
+}
+
+} // namespace
+
+void ScrollEventHelper::registerNatives() {
+  javaClassLocal()->registerNatives({
+      makeNativeMethod("nativeCreateScrollPayload", createScrollPayload),
+  });
+}
+
+} // namespace facebook::react

packages/react-native/ReactAndroid/src/main/jni/react/jni/ScrollEventHelper.h

@@ -0,0 +1,21 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include <fbjni/fbjni.h>
+
+namespace facebook::react {
+
+class ScrollEventHelper : public jni::JavaClass<ScrollEventHelper> {
+ public:
+  static auto constexpr *kJavaDescriptor = "Lcom/facebook/react/views/scroll/ScrollEventHelper;";
+
+  static void registerNatives();
+};
+
+} // namespace facebook::react

scripts/cxx-api/api-snapshots/ReactAndroidDebugCxx.api

@@ -2203,6 +2203,11 @@ class facebook::react::SafeAreaViewProps : public facebook::react::HostPlatformV
   public virtual folly::dynamic getDiffProps(const facebook::react::Props* prevProps) const override;
 }
 
+class facebook::react::ScrollEventHelper : public facebook::jni::JavaClass<facebook::react::ScrollEventHelper> {
+  public static constexpr auto * kJavaDescriptor;
+  public static void registerNatives();
+}
+
 class facebook::react::Sealable {
   public Sealable();
   public Sealable(const facebook::react::Sealable& other);

scripts/cxx-api/api-snapshots/ReactAndroidFrameworksCxx.api

@@ -3567,6 +3567,11 @@ class facebook::react::SchedulerDelegate {
   public virtual ~SchedulerDelegate() noexcept = default;
 }
 
+class facebook::react::ScrollEventHelper : public facebook::jni::JavaClass<facebook::react::ScrollEventHelper> {
+  public static constexpr auto * kJavaDescriptor;
+  public static void registerNatives();
+}
+
 class facebook::react::ScrollViewEventEmitter : public facebook::react::BaseViewEventEmitter {
   public using EndDragMetrics = facebook::react::ScrollEndDragEvent;
   public using Metrics = facebook::react::ScrollEvent;

scripts/cxx-api/api-snapshots/ReactAndroidNewarchCxx.api

@@ -2202,6 +2202,11 @@ class facebook::react::SafeAreaViewProps : public facebook::react::HostPlatformV
   public virtual folly::dynamic getDiffProps(const facebook::react::Props* prevProps) const override;
 }
 
+class facebook::react::ScrollEventHelper : public facebook::jni::JavaClass<facebook::react::ScrollEventHelper> {
+  public static constexpr auto * kJavaDescriptor;
+  public static void registerNatives();
+}
+
 class facebook::react::Sealable {
   public bool getSealed() const;
   public void ensureUnsealed() const;

scripts/cxx-api/api-snapshots/ReactAndroidReleaseCxx.api

@@ -2202,6 +2202,11 @@ class facebook::react::SafeAreaViewProps : public facebook::react::HostPlatformV
   public virtual folly::dynamic getDiffProps(const facebook::react::Props* prevProps) const override;
 }
 
+class facebook::react::ScrollEventHelper : public facebook::jni::JavaClass<facebook::react::ScrollEventHelper> {
+  public static constexpr auto * kJavaDescriptor;
+  public static void registerNatives();
+}
+
 class facebook::react::Sealable {
   public bool getSealed() const;
   public void ensureUnsealed() const;