Only collect state from nodes that have been updated

Summary: We are currently traversing entire tree every time there is any update to any of the nodes, which is hugely inefficient. Instead, we can early out for nodes that are known to contain no updates. This saves a lof of CPU. This optimization can be turned off, and an Exception will be thrown if there was an unexpected update.

Reviewed By: ahmedre

Differential Revision: D2975706

ReactAndroid/src/main/java/com/facebook/react/flat/FlatShadowNode.java

@@ -52,6 +52,10 @@ import com.facebook.react.uimanager.annotations.ReactProp;
   private int mMoveToIndexInParent;
   private boolean mClipToBounds = false;
   private boolean mIsUpdated = true;
+  private float mClipLeft;
+  private float mClipTop;
+  private float mClipRight;
+  private float mClipBottom;
 
   // last OnLayoutEvent info, only used when shouldNotifyOnLayout() is true.
   private int mLayoutX;
@@ -174,6 +178,26 @@ import com.facebook.react.uimanager.annotations.ReactProp;
     mIsUpdated = false;
   }
 
+  /* package */ final boolean clipBoundsChanged(
+      float clipLeft,
+      float clipTop,
+      float clipRight,
+      float clipBottom) {
+    return mClipLeft != clipLeft || mClipTop != clipTop ||
+        mClipRight != clipRight || mClipBottom != clipBottom;
+  }
+
+  /* package */ final void setClipBounds(
+      float clipLeft,
+      float clipTop,
+      float clipRight,
+      float clipBottom) {
+    mClipLeft = clipLeft;
+    mClipTop = clipTop;
+    mClipRight = clipRight;
+    mClipBottom = clipBottom;
+  }
+
   /**
    * Returns an array of DrawCommands to perform during the View's draw pass.
    */

ReactAndroid/src/main/java/com/facebook/react/flat/FlatUIImplementation.java

@@ -402,23 +402,13 @@ public class FlatUIImplementation extends UIImplementation {
     parentNode.addChildAt(childNode, index);
   }
 
-  @Override
-  protected void calculateRootLayout(ReactShadowNode cssRoot) {
-  }
-
   @Override
   protected void applyUpdatesRecursive(
       ReactShadowNode cssNode,
       float absoluteX,
       float absoluteY,
       EventDispatcher eventDispatcher) {
-    FlatRootShadowNode rootNode = (FlatRootShadowNode) cssNode;
-    if (!rootNode.needsLayout() && !rootNode.isUpdated()) {
-      return;
-    }
-
-    super.calculateRootLayout(rootNode);
-    mStateBuilder.applyUpdates(eventDispatcher, rootNode);
+    mStateBuilder.applyUpdates(eventDispatcher, (FlatRootShadowNode) cssNode);
   }
 
   @Override

ReactAndroid/src/main/java/com/facebook/react/flat/StateBuilder.java

@@ -27,6 +27,8 @@ import com.facebook.react.uimanager.events.EventDispatcher;
  */
 /* package */ final class StateBuilder {
 
+  private static final boolean SKIP_UP_TO_DATE_NODES = true;
+
   private static final int[] EMPTY_INT_ARRAY = new int[0];
 
   private final FlatUIViewOperationQueue mOperationsQueue;
@@ -225,8 +227,9 @@ import com.facebook.react.uimanager.events.EventDispatcher;
 
   /**
    * Collects state (DrawCommands) for a given node that will mount to a View.
+   * Returns true if this node or any of its descendants that mount to View generated any updates.
    */
-  private void collectStateForMountableNode(
+  private boolean collectStateForMountableNode(
       FlatShadowNode node,
       float left,
       float top,
@@ -236,6 +239,18 @@ import com.facebook.react.uimanager.events.EventDispatcher;
       float clipTop,
       float clipRight,
       float clipBottom) {
+    // Normally, this would be a node.hasNewLayout() check, but we also need to check if a node
+    // needs onCollectExtraUpdates() call.
+    boolean hasUpdates = node.hasUpdates();
+
+    boolean expectingUpdate = hasUpdates || node.isUpdated() ||
+        node.clipBoundsChanged(clipLeft, clipTop, clipRight, clipBottom);
+    if (SKIP_UP_TO_DATE_NODES && !expectingUpdate) {
+      return false;
+    }
+
+    node.setClipBounds(clipLeft, clipTop, clipRight, clipBottom);
+
     mDrawCommands.start(node.getDrawCommands());
     mAttachDetachListeners.start(node.getAttachDetachListeners());
     mNodeRegions.start(node.getNodeRegions());
@@ -259,7 +274,7 @@ import com.facebook.react.uimanager.events.EventDispatcher;
       clipBottom = Float.POSITIVE_INFINITY;
     }
 
-    collectStateRecursively(
+    boolean descendantUpdated = collectStateRecursively(
         node,
         left,
         top,
@@ -308,7 +323,7 @@ import com.facebook.react.uimanager.events.EventDispatcher;
           nodeRegions);
     }
 
-    if (node.hasUpdates()) {
+    if (hasUpdates) {
       node.onCollectExtraUpdates(mOperationsQueue);
       node.markUpdateSeen();
     }
@@ -317,6 +332,14 @@ import com.facebook.react.uimanager.events.EventDispatcher;
     if (nativeChildren != null) {
       updateNativeChildren(node, node.getNativeChildren(), nativeChildren);
     }
+
+    boolean updated = shouldUpdateMountState || nativeChildren != null || descendantUpdated;
+
+    if (!expectingUpdate && updated) {
+      throw new RuntimeException("Node " + node.getReactTag() + " updated unexpectedly.");
+    }
+
+    return updated;
   }
 
   private void updateNativeChildren(
@@ -378,7 +401,7 @@ import com.facebook.react.uimanager.events.EventDispatcher;
   /**
    * Recursively walks node tree from a given node and collects DrawCommands.
    */
-  private void collectStateRecursively(
+  private boolean collectStateRecursively(
       FlatShadowNode node,
       float left,
       float top,
@@ -429,6 +452,7 @@ import com.facebook.react.uimanager.events.EventDispatcher;
         roundToPixel(clipRight),
         clipBottom);
 
+    boolean updated = false;
     for (int i = 0, childCount = node.getChildCount(); i != childCount; ++i) {
       ReactShadowNode child = node.getChildAt(i);
       if (child.isVirtual()) {
@@ -436,7 +460,7 @@ import com.facebook.react.uimanager.events.EventDispatcher;
         continue;
       }
 
-      processNodeAndCollectState(
+      updated |= processNodeAndCollectState(
           (FlatShadowNode) child,
           left,
           top,
@@ -449,6 +473,8 @@ import com.facebook.react.uimanager.events.EventDispatcher;
     }
 
     node.resetUpdated();
+
+    return updated;
   }
 
   private void markLayoutSeenRecursively(ReactShadowNode node) {
@@ -463,8 +489,9 @@ import com.facebook.react.uimanager.events.EventDispatcher;
 
   /**
    * Collects state and updates View boundaries for a given node tree.
+   * Returns true if this node or any of its descendants that mount to View generated any updates.
    */
-  private void processNodeAndCollectState(
+  private boolean processNodeAndCollectState(
       FlatShadowNode node,
       float parentLeft,
       float parentTop,
@@ -482,6 +509,8 @@ import com.facebook.react.uimanager.events.EventDispatcher;
     float right = left + width;
     float bottom = top + height;
 
+    final boolean updated;
+
     if (node.mountsToView()) {
       ensureBackingViewIsCreated(node);
 
@@ -494,7 +523,7 @@ import com.facebook.react.uimanager.events.EventDispatcher;
             parentClipBottom));
       }
 
-      collectStateForMountableNode(
+      updated = collectStateForMountableNode(
           node,
           left - left,
           top - top,
@@ -509,7 +538,7 @@ import com.facebook.react.uimanager.events.EventDispatcher;
         updateViewBounds(node, left, top, right, bottom);
       }
     } else {
-      collectStateRecursively(
+      updated = collectStateRecursively(
           node,
           left,
           top,
@@ -523,6 +552,8 @@ import com.facebook.react.uimanager.events.EventDispatcher;
           false);
       addNodeRegion(node, left, top, right, bottom);
     }
+
+    return updated;
   }
 
   private void updateViewPadding(AndroidView androidView, int reactTag) {