Fix visibilityChanged event MountState calculations

Summary:
The visibilityChanged event is using the incorrect rectangles to calculate percent visibility. This is visible in the test added and also affects nested LithoView situations (like when used in a VeriticalScroll component).

The old calculation used the layoutState and localVisibleRect

The new calculation uses the visibilityOutputBounds and the intersection of the visibilityOutputBounds and localVisibleRect

See D7377488 where I made a similar fix for the visibleRatio calculation
 ---
`localVisibleRect` represents the full screen (in the test, Rect(left=0, top=0, right=10, bottom=1000))
`visibilityOutputBounds` represents the renderedComponent (in the test, Rect(left=0, top=0, right=10, bottom=10)

`sTempRect` represents the intersection of localVisibleRect and visibilityOutputBounds, essentially the part of the component that is visible on screen (in the initial mount of the test, Rect(left=0, top=0, right=10, bottom=10)

Therefore it follows if we want to calculate the amount on screen, we use `sTempRect` to get the width/height of the visible component and then divide by visibilityOutputBounds to get the percent of the component that is visible.

Reviewed By: mihaelao

Differential Revision: D14377550

fbshipit-source-id: 8e98c53f07bbbf1023ea71fbd8dfe82dee02dce1

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

@@ -637,14 +637,14 @@ void processVisibilityOutputs(
         }
 
         if (visibilityChangedHandler != null) {
-          final int visibleWidth = localVisibleRect.right - localVisibleRect.left;
-          final int visibleHeight = localVisibleRect.bottom - localVisibleRect.top;
+          final int visibleWidth = sTempRect.right - sTempRect.left;
+          final int visibleHeight = sTempRect.bottom - sTempRect.top;
           EventDispatcherUtils.dispatchOnVisibilityChanged(
               visibilityChangedHandler,
               visibleWidth,
               visibleHeight,
-              100f * visibleWidth / layoutState.getWidth(),
-              100f * visibleHeight / layoutState.getHeight());
+              100f * visibleWidth / visibilityOutputBounds.width(),
+              100f * visibleHeight / visibilityOutputBounds.height());
         }
       }
       if (isDoingPerfLog) {

litho-it/src/test/java/com/facebook/litho/VisibilityEventsTest.java

@@ -460,6 +460,60 @@ public void testVisibleRectChangedEventItemNotVisible() {
     assertThat(visibilityChangedEvent.percentVisibleWidth).isEqualTo(0.0f);
   }
 
+  @Test
+  public void testVisibleRectChangedEventLargeView() {
+    final TestComponent content = create(mContext).build();
+    final EventHandler<VisibilityChangedEvent> visibilityChangedHandler =
+        new EventHandler<>(content, 3);
+
+    final LithoView lithoView =
+        mountComponent(
+            mContext,
+            mLithoView,
+            Column.create(mContext)
+                .child(
+                    Wrapper.create(mContext)
+                        .delegate(content)
+                        .visibilityChangedHandler(visibilityChangedHandler)
+                        .widthPx(10)
+                        .heightPx(10))
+                .build(),
+            true,
+            10,
+            1000);
+
+    VisibilityChangedEvent visibilityChangedEvent =
+        (VisibilityChangedEvent) content.getEventState(visibilityChangedHandler);
+    assertThat(visibilityChangedEvent.visibleHeight).isEqualTo(10);
+    assertThat(visibilityChangedEvent.visibleWidth).isEqualTo(10);
+    assertThat(visibilityChangedEvent.percentVisibleHeight).isEqualTo(100f);
+    assertThat(visibilityChangedEvent.percentVisibleWidth).isEqualTo(100f);
+
+    content.getDispatchedEventHandlers().clear();
+
+    lithoView.performIncrementalMount(new Rect(LEFT, 0, RIGHT, 4), true);
+    assertThat(content.getDispatchedEventHandlers()).contains(visibilityChangedHandler);
+
+    visibilityChangedEvent =
+        (VisibilityChangedEvent) content.getEventState(visibilityChangedHandler);
+
+    assertThat(visibilityChangedEvent.visibleHeight).isEqualTo(4);
+    assertThat(visibilityChangedEvent.visibleWidth).isEqualTo(10);
+    assertThat(visibilityChangedEvent.percentVisibleHeight).isEqualTo(40f);
+    assertThat(visibilityChangedEvent.percentVisibleWidth).isEqualTo(100f);
+
+    lithoView.performIncrementalMount(new Rect(LEFT, 0, RIGHT, 5), true);
+    assertThat(content.getDispatchedEventHandlers()).contains(visibilityChangedHandler);
+
+    visibilityChangedEvent =
+        (VisibilityChangedEvent) content.getEventState(visibilityChangedHandler);
+
+    assertThat(visibilityChangedEvent.visibleHeight).isEqualTo(5);
+    assertThat(visibilityChangedEvent.visibleWidth).isEqualTo(10);
+    assertThat(visibilityChangedEvent.percentVisibleHeight).isEqualTo(50f);
+    assertThat(visibilityChangedEvent.percentVisibleWidth).isEqualTo(100f);
+  }
+
   @Test
   public void testVisibleAndInvisibleEvents() {
     final TestComponent content = create(mContext).build();