performPaint method

Implementation

@override
void performPaint(PaintingContext context, Offset offset) {
  // Report FCP/LCP when RenderWidget with contentful Flutter widget is first painted
  if (renderStyle.target is WidgetElement && firstChild != null && hasSize && !size.isEmpty) {
    final widgetElement = renderStyle.target as WidgetElement;

    // Check if the widget contains contentful content and get the actual visible area
    double contentfulArea = _getContentfulPaintArea(widgetElement);
    if (contentfulArea > 0) {
      // Report FP first (if not already reported)
      widgetElement.ownerDocument.controller.reportFP();
      widgetElement.ownerDocument.controller.reportFCP();

      // Report LCP candidate with the actual contentful area
      widgetElement.ownerDocument.controller.reportLCPCandidate(widgetElement, contentfulArea);
    }
  }

  Offset _accumulateOffsetFromDescendant(RenderObject descendant, RenderObject ancestor) {
    Offset sum = Offset.zero;
    RenderObject? cur = descendant;
    while (cur != null && cur != ancestor) {
      final Object? pd = (cur is RenderBox) ? (cur.parentData) : null;
      if (pd is ContainerBoxParentData) {
        sum += (pd as ContainerBoxParentData).offset;
      } else if (pd is RenderLayoutParentData) {
        sum += (pd as RenderLayoutParentData).offset;
      }
      cur = cur.parent as RenderObject?;
    }
    return sum;
  }

  for (final RenderBox child in paintingOrder) {
    if (isPositionPlaceholder(child)) continue;
    final RenderLayoutParentData pd = child.parentData as RenderLayoutParentData;
    if (!child.hasSize) continue;

    bool restoreFlag = false;
    bool previous = false;
    final bool promoteHere = (renderStyle as CSSRenderStyle).isDocumentRootBox();
    if (promoteHere && child is RenderBoxModel) {
      final CSSRenderStyle rs = child.renderStyle;
      final int? zi = rs.zIndex;
      final bool isPositive = zi != null && zi > 0;
      if (!isPositive) {
        previous = rs.suppressPositiveStackingFromDescendants;
        rs.suppressPositiveStackingFromDescendants = true;
        if (child is RenderLayoutBox) {
          child.markChildrenNeedsSort();
        } else if (child is RenderWidget) {
          child.markChildrenNeedsSort();
        }
        restoreFlag = true;
      }
    }

    final bool direct = identical(child.parent, this);
    final Offset localOffset = direct ? pd.offset : _accumulateOffsetFromDescendant(child, this);
    context.paintChild(child, offset + localOffset);

    if (restoreFlag && child is RenderBoxModel) {
      (child.renderStyle as CSSRenderStyle).suppressPositiveStackingFromDescendants = previous;
      if (child is RenderLayoutBox) {
        child.markChildrenNeedsSort();
      } else if (child is RenderWidget) {
        child.markChildrenNeedsSort();
      }
    }
  }
}