private void performIncrementalMount()

in litho-core/src/main/java/com/facebook/litho/MountState.java [2536:2639]
90 lines of code
23 McCabe index (conditional complexity)

  private void performIncrementalMount(
      LayoutState layoutState, Rect localVisibleRect, boolean processVisibilityOutputs) {

    final boolean isTracing = RenderCoreSystrace.isEnabled();

    if (isTracing) {
      RenderCoreSystrace.beginSection("performIncrementalMount");
    }

    final ArrayList<IncrementalMountOutput> layoutOutputTops =
        layoutState.getOutputsOrderedByTopBounds();
    final ArrayList<IncrementalMountOutput> layoutOutputBottoms =
        layoutState.getOutputsOrderedByBottomBounds();
    final int count = layoutState.getMountableOutputCount();

    if (localVisibleRect.top >= 0 || mPreviousLocalVisibleRect.top >= 0) {
      // View is going on/off the top of the screen. Check the bottoms to see if there is anything
      // that has moved on/off the top of the screen.
      while (mPreviousBottomsIndex < count
          && localVisibleRect.top
              >= layoutOutputBottoms.get(mPreviousBottomsIndex).getBounds().bottom) {
        final RenderTreeNode node =
            layoutState.getRenderTreeNode(layoutOutputBottoms.get(mPreviousBottomsIndex));
        final long id = node.getRenderUnit().getId();
        final int layoutOutputIndex = layoutState.getPositionForId(id);
        if (!isAnimationLocked(node)) {
          unmountItem(layoutOutputIndex, mHostsByMarker);
        }
        mPreviousBottomsIndex++;
      }

      while (mPreviousBottomsIndex > 0
          && localVisibleRect.top
              <= layoutOutputBottoms.get(mPreviousBottomsIndex - 1).getBounds().bottom) {
        mPreviousBottomsIndex--;
        final RenderTreeNode node =
            layoutState.getRenderTreeNode(layoutOutputBottoms.get(mPreviousBottomsIndex));
        final LayoutOutput layoutOutput = getLayoutOutput(node);
        final int layoutOutputIndex = layoutState.getPositionForId(node.getRenderUnit().getId());
        if (getItemAt(layoutOutputIndex) == null) {
          mountLayoutOutput(
              layoutState.getPositionForId(node.getRenderUnit().getId()),
              node,
              layoutOutput,
              layoutState);
          mComponentIdsMountedInThisFrame.add(node.getRenderUnit().getId());
        }
      }
    }

    final int height = mLithoView.getHeight();
    if (localVisibleRect.bottom < height || mPreviousLocalVisibleRect.bottom < height) {
      // View is going on/off the bottom of the screen. Check the tops to see if there is anything
      // that has changed.
      while (mPreviousTopsIndex < count
          && localVisibleRect.bottom >= layoutOutputTops.get(mPreviousTopsIndex).getBounds().top) {
        final RenderTreeNode node =
            layoutState.getRenderTreeNode(layoutOutputTops.get(mPreviousTopsIndex));
        final LayoutOutput layoutOutput = getLayoutOutput(node);
        final int layoutOutputIndex = layoutState.getPositionForId(node.getRenderUnit().getId());
        if (getItemAt(layoutOutputIndex) == null) {
          mountLayoutOutput(
              layoutState.getPositionForId(node.getRenderUnit().getId()),
              node,
              layoutOutput,
              layoutState);
          mComponentIdsMountedInThisFrame.add(node.getRenderUnit().getId());
        }
        mPreviousTopsIndex++;
      }

      while (mPreviousTopsIndex > 0
          && localVisibleRect.bottom
              < layoutOutputTops.get(mPreviousTopsIndex - 1).getBounds().top) {
        mPreviousTopsIndex--;
        final RenderTreeNode node =
            layoutState.getRenderTreeNode(layoutOutputTops.get(mPreviousTopsIndex));
        final long id = node.getRenderUnit().getId();
        final int layoutOutputIndex = layoutState.getPositionForId(id);
        if (!isAnimationLocked(node)) {
          unmountItem(layoutOutputIndex, mHostsByMarker);
        }
      }
    }

    if (!mLithoView.skipNotifyVisibleBoundsChangedCalls()) {
      for (int i = 0, size = mCanMountIncrementallyMountItems.size(); i < size; i++) {
        final MountItem mountItem = mCanMountIncrementallyMountItems.valueAt(i);
        final long layoutOutputId = mCanMountIncrementallyMountItems.keyAt(i);
        if (!mComponentIdsMountedInThisFrame.contains(layoutOutputId)) {
          final int layoutOutputPosition = layoutState.getPositionForId(layoutOutputId);
          if (layoutOutputPosition != -1) {
            mountItemIncrementally(mountItem, processVisibilityOutputs);
          }
        }
      }
    }

    mComponentIdsMountedInThisFrame.clear();

    if (isTracing) {
      RenderCoreSystrace.endSection();
    }
  }