private void updateLastTopLeftCornerOffset() {
    int visibleAreaTopY = myEditor.getScrollingModel().getVisibleArea().y;
    if (visibleAreaTopY == 0) {
      myLastTopLeftCornerOffset = 0;
    }
    else {
      int visualLine = 1 + myEditor.yToVisualLine(visibleAreaTopY);
      myLastTopLeftCornerOffset = myEditor.visualLineStartOffset(visualLine);
    }
  }
private void updateLastTopLeftCornerOffset()