Ensure elevated views are not changing drawing order

Summary:
Uses `enableZ` trick to ensure that Skia doesn't try to reorder the views based on elevation. Unfortunately, it only helps for some cases, but the proper fix would require reimplementing `ViewGroup` completely to remove its internal logic of reordering based on Z coordinate.

Changelog: [Android][Fixed] Ensure elevated views are behind sticky header in FlatList

Reviewed By: cortinico

Differential Revision: D30700566

fbshipit-source-id: d2c59b22332922c610f4f2d415df34e81f5a33c5

ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java

@@ -95,4 +95,6 @@ public class ReactFeatureFlags {
   public static boolean enableLockFreeEventDispatcher = false;
 
   public static boolean enableAggressiveEventEmitterCleanup = false;
+
+  public static boolean insertZReorderBarriersOnViewGroupChildren = true;
 }

ReactAndroid/src/main/java/com/facebook/react/views/view/CanvasUtil.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright (c) Facebook, Inc. and its 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.view;
+
+import android.annotation.SuppressLint;
+import android.graphics.Canvas;
+import android.os.Build;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import javax.annotation.Nullable;
+
+/**
+ * Copied from <a
+ * href="https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:compose/ui/ui-graphics/src/androidMain/kotlin/androidx/compose/ui/graphics/CanvasUtils.android.kt;drc=3b2dde134afab8d58b9c39ad4820eaf9a6e014a9">
+ * Compose canvas utils </a>
+ */
+public class CanvasUtil {
+  private CanvasUtil() {}
+
+  private @Nullable static Method mReorderBarrierMethod = null;
+  private @Nullable static Method mInorderBarrierMethod = null;
+  private static boolean mOrderMethodsFetched = false;
+
+  /**
+   * Enables Z support for the Canvas. The method is publicly available starting from API 29 and was
+   * hidden before, so we have to resort to reflection tricks to ensure we can use this API.
+   */
+  @SuppressLint({"SoonBlockedPrivateApi", "PrivateApi"})
+  public static void enableZ(Canvas canvas, boolean enable) {
+    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {
+      return;
+    }
+
+    if (Build.VERSION.SDK_INT >= 29) {
+      if (enable) {
+        canvas.enableZ();
+      } else {
+        canvas.disableZ();
+      }
+    } else {
+      fetchOrderMethods();
+      try {
+        if (enable && mReorderBarrierMethod != null) {
+          mReorderBarrierMethod.invoke(canvas);
+        }
+        if (!enable && mInorderBarrierMethod != null) {
+          mInorderBarrierMethod.invoke(canvas);
+        }
+      } catch (IllegalAccessException | InvocationTargetException ignore) {
+        // Do nothing
+      }
+    }
+  }
+
+  private static void fetchOrderMethods() {
+    if (!mOrderMethodsFetched) {
+      try {
+        if (Build.VERSION.SDK_INT == Build.VERSION_CODES.P) {
+          // use double reflection to avoid grey list on P
+          Method getDeclaredMethod =
+              Class.class.getDeclaredMethod("getDeclaredMethod", String.class, Class[].class);
+          mReorderBarrierMethod =
+              (Method) getDeclaredMethod.invoke(Canvas.class, "insertReorderBarrier", new Class[0]);
+          mInorderBarrierMethod =
+              (Method) getDeclaredMethod.invoke(Canvas.class, "insertInorderBarrier", new Class[0]);
+        } else {
+          mReorderBarrierMethod = Canvas.class.getDeclaredMethod("insertReorderBarrier");
+          mInorderBarrierMethod = Canvas.class.getDeclaredMethod("insertInorderBarrier");
+        }
+
+        if (mReorderBarrierMethod == null || mInorderBarrierMethod == null) {
+          return;
+        }
+
+        mReorderBarrierMethod.setAccessible(true);
+        mInorderBarrierMethod.setAccessible(true);
+      } catch (IllegalAccessException ignore) {
+        // Do nothing
+      } catch (InvocationTargetException ignore) {
+        // Do nothing
+      } catch (NoSuchMethodException ignore) {
+        // Do nothing
+      }
+      mOrderMethodsFetched = true;
+    }
+  }
+}

ReactAndroid/src/main/java/com/facebook/react/views/view/ReactViewGroup.java

@@ -33,6 +33,7 @@ import com.facebook.react.bridge.ReactNoCrashSoftException;
 import com.facebook.react.bridge.ReactSoftExceptionLogger;
 import com.facebook.react.bridge.UiThreadUtil;
 import com.facebook.react.common.annotations.VisibleForTesting;
+import com.facebook.react.config.ReactFeatureFlags;
 import com.facebook.react.modules.i18nmanager.I18nUtil;
 import com.facebook.react.touch.OnInterceptTouchEventListener;
 import com.facebook.react.touch.ReactHitSlopView;
@@ -759,6 +760,23 @@ public class ReactViewGroup extends ViewGroup
     }
   }
 
+  @Override
+  protected boolean drawChild(Canvas canvas, View child, long drawingTime) {
+    boolean drawWithZ =
+        child.getElevation() > 0 && ReactFeatureFlags.insertZReorderBarriersOnViewGroupChildren;
+
+    if (drawWithZ) {
+      CanvasUtil.enableZ(canvas, false);
+    }
+
+    boolean result = super.drawChild(canvas, child, drawingTime);
+
+    if (drawWithZ) {
+      CanvasUtil.enableZ(canvas, true);
+    }
+    return result;
+  }
+
   private void dispatchOverflowDraw(Canvas canvas) {
     if (mOverflow != null) {
       switch (mOverflow) {