Add events for Incremental Mount Start/End.

Summary: Adding support for events for Incremental Mount Start/End so we can visualize the mount related events that happen in a IM pass.

Reviewed By: LukeDefeo

Differential Revision: D51805156

fbshipit-source-id: fbfb93d3a40d09fa6cfbc6b10dcad781aac08af2

litho-core/src/main/java/com/facebook/litho/BaseMountingView.java

@@ -40,6 +40,9 @@
 import com.facebook.rendercore.RenderCoreExtensionHost;
 import com.facebook.rendercore.RenderTree;
 import com.facebook.rendercore.RenderTreeUpdateListener;
+import com.facebook.rendercore.debug.DebugEvent;
+import com.facebook.rendercore.debug.DebugEventAttribute;
+import com.facebook.rendercore.debug.DebugEventDispatcher;
 import com.facebook.rendercore.extensions.RenderCoreExtension;
 import com.facebook.rendercore.transitions.AnimatedRootHost;
 import com.facebook.rendercore.visibility.VisibilityOutput;
@@ -48,6 +51,7 @@
 import java.util.ArrayList;
 import java.util.Deque;
 import java.util.List;
+import kotlin.Unit;
 
 public abstract class BaseMountingView extends ComponentHost
     implements RenderCoreExtensionHost, AnimatedRootHost {
@@ -691,6 +695,7 @@ public void setSkipMountingIfNotVisible(boolean skipMountingIfNotVisible) {
   @UiThread
   void performIncrementalMountForVisibleBoundsChange() {
     assertMainThread();
+
     if (!hasTree()) {
       return;
     }
@@ -700,6 +705,15 @@ void performIncrementalMountForVisibleBoundsChange() {
     final Rect currentVisibleArea = new Rect();
     final boolean areBoundsVisible = getLocalVisibleRect(currentVisibleArea);
 
+    DebugEventDispatcher.dispatch(
+        DebugEvent.IncrementalMountStart,
+        () -> String.valueOf(mMountState.getRenderStateId()),
+        attrs -> {
+          attrs.put(DebugEventAttribute.VisibleRect, currentVisibleArea);
+          attrs.put(DebugEventAttribute.BoundsVisible, areBoundsVisible);
+          return Unit.INSTANCE;
+        });
+
     if (areBoundsVisible
         || hasComponentsExcludedFromIncrementalMount(getCurrentLayoutState())
         // It might not be yet visible but animating from 0 height/width in which case we still
@@ -708,6 +722,11 @@ void performIncrementalMountForVisibleBoundsChange() {
         || hasBecomeInvisible()) {
       mountComponent(currentVisibleArea, true);
     }
+
+    DebugEventDispatcher.dispatch(
+        DebugEvent.IncrementalMountEnd,
+        () -> String.valueOf(mMountState.getRenderStateId()),
+        attrs -> Unit.INSTANCE);
   }
 
   /**

litho-rendercore/src/main/java/com/facebook/rendercore/debug/DebugEvents.kt

@@ -43,6 +43,8 @@ sealed class DebugEvent(
     const val RenderUnitOnVisible = "RenderCore.RenderUnit.OnVisible"
     const val RenderUnitOnInvisible = "RenderCore.RenderUnit.OnInvisible"
     const val ViewOnLayout = "RenderCore.View.OnLayout"
+    const val IncrementalMountStart = "RenderCore.IncrementalMount.Start"
+    const val IncrementalMountEnd = "RenderCore.IncrementalMount.End"
   }
 
   /** Returns the value of attribute with [name]. */
@@ -93,6 +95,8 @@ object DebugEventAttribute {
   const val RootHostHashCode = "rootHostHashCode"
   const val Name = "name"
   const val Key = "key"
+  const val VisibleRect = "visibleRect"
+  const val BoundsVisible = "areBoundsVisible"
 }
 
 /** Base class for marker events */