From c54775791353e37aa621cf5dd6cf7d82c2762799 Mon Sep 17 00:00:00 2001
From: Joshua Gross <joshuagross@fb.com>
Date: Wed, 7 Oct 2020 23:10:48 -0700
Subject: [PATCH] Perf improvement: don't call uiManager.updateRootLayoutSpecs
 on every ReactRootView.onLayout

Summary:
In D23640968 (https://github.com/facebook/react-native/commit/78b42d7fb7180102c1e8ec917dcccd2d9d4076db) I introduced a mechanism to update offsetX/offsetY whenever onMeasure/onLayout were called, to ensure that `measureInWindow` had the correct metrics and would work properly.

However, now `uiManager.updateRootLayoutSpecs` gets spammed and is called too often. For example, whenever a TextInput is focused/blurred, `uiManager.updateRootLayoutSpecs` may be called 5+ times even though
the measure specs/offsets may only change once.

Thus, we just compare with previous values before calling into the UIManager. This should give us a very small perf improvement.

Changelog: [Internal]

Reviewed By: shergin

Differential Revision: D24176867

fbshipit-source-id: f0dcc816e651a843607e9e5d40d8f3489894d4ba
---
 .../com/facebook/react/ReactRootView.java     | 28 +++++++++++++++----
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/ReactAndroid/src/main/java/com/facebook/react/ReactRootView.java b/ReactAndroid/src/main/java/com/facebook/react/ReactRootView.java
index c21bffc720a..30b322a68a3 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/ReactRootView.java
+++ b/ReactAndroid/src/main/java/com/facebook/react/ReactRootView.java
@@ -95,6 +95,8 @@ public class ReactRootView extends FrameLayout implements RootView, ReactRoot {
   private int mHeightMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);
   private int mLastWidth = 0;
   private int mLastHeight = 0;
+  private int mLastOffsetX = Integer.MIN_VALUE;
+  private int mLastOffsetY = Integer.MIN_VALUE;
   private @UIManagerType int mUIManagerType = DEFAULT;
 
   public ReactRootView(Context context) {
@@ -162,7 +164,7 @@ public class ReactRootView extends FrameLayout implements RootView, ReactRoot {
       if (mReactInstanceManager != null && !mIsAttachedToInstance) {
         attachToReactInstanceManager();
       } else if (measureSpecsUpdated || mLastWidth != width || mLastHeight != height) {
-        updateRootLayoutSpecs(mWidthMeasureSpec, mHeightMeasureSpec);
+        updateRootLayoutSpecs(true, mWidthMeasureSpec, mHeightMeasureSpec);
       }
       mLastWidth = width;
       mLastHeight = height;
@@ -296,7 +298,7 @@ public class ReactRootView extends FrameLayout implements RootView, ReactRoot {
 
     // In Fabric, update LayoutSpecs just so we update the offsetX and offsetY.
     if (mWasMeasured && getUIManagerType() == FABRIC) {
-      updateRootLayoutSpecs(mWidthMeasureSpec, mHeightMeasureSpec);
+      updateRootLayoutSpecs(false, mWidthMeasureSpec, mHeightMeasureSpec);
     }
   }
 
@@ -423,7 +425,17 @@ public class ReactRootView extends FrameLayout implements RootView, ReactRoot {
     return new Point(locationInWindow[0], locationInWindow[1]);
   }
 
-  private void updateRootLayoutSpecs(final int widthMeasureSpec, final int heightMeasureSpec) {
+  /**
+   * Call whenever measure specs change, or if you want to force an update of offsetX/offsetY. If
+   * measureSpecsChanged is false and the offsetX/offsetY don't change, updateRootLayoutSpecs will
+   * not be called on the UIManager as a perf optimization.
+   *
+   * @param measureSpecsChanged
+   * @param widthMeasureSpec
+   * @param heightMeasureSpec
+   */
+  private void updateRootLayoutSpecs(
+      boolean measureSpecsChanged, final int widthMeasureSpec, final int heightMeasureSpec) {
     if (mReactInstanceManager == null) {
       FLog.w(TAG, "Unable to update root layout specs for uninitialized ReactInstanceManager");
       return;
@@ -445,8 +457,12 @@ public class ReactRootView extends FrameLayout implements RootView, ReactRoot {
           offsetY = viewportOffset.y;
         }
 
-        uiManager.updateRootLayoutSpecs(
-            getRootViewTag(), widthMeasureSpec, heightMeasureSpec, offsetX, offsetY);
+        if (measureSpecsChanged || offsetX != mLastOffsetX || offsetY != mLastOffsetY) {
+          uiManager.updateRootLayoutSpecs(
+              getRootViewTag(), widthMeasureSpec, heightMeasureSpec, offsetX, offsetY);
+        }
+        mLastOffsetX = offsetX;
+        mLastOffsetY = offsetY;
       }
     }
   }
@@ -558,7 +574,7 @@ public class ReactRootView extends FrameLayout implements RootView, ReactRoot {
       String jsAppModuleName = getJSModuleName();
 
       if (mWasMeasured) {
-        updateRootLayoutSpecs(mWidthMeasureSpec, mHeightMeasureSpec);
+        updateRootLayoutSpecs(true, mWidthMeasureSpec, mHeightMeasureSpec);
       }
 
       WritableNativeMap appParams = new WritableNativeMap();