void repaintCompositedChild(RenderObject child, { bool debugAlsoPaintedParent: false })

Repaint the given render object.

The render object must have a composited layer and must be in need of painting. The render object's layer is re-used, along with any layers in the subtree that don't need to be repainted.

Source 

static void repaintCompositedChild(RenderObject child, { bool debugAlsoPaintedParent: false }) {
  assert(child.isRepaintBoundary);
  assert(child._needsPaint);
  assert(() {
    child.debugRegisterRepaintBoundaryPaint(includedParent: debugAlsoPaintedParent, includedChild: true);
    return true;
  });
  child._layer ??= new OffsetLayer();
  child._layer.removeAllChildren();
  assert(() {
    child._layer.debugCreator = child.debugCreator ?? child.runtimeType;
    return true;
  });
  PaintingContext childContext = new PaintingContext._(child._layer, child.paintBounds);
  child._paintWithContext(childContext, Offset.zero);
  childContext._stopRecordingIfNeeded();
}