const x = PADDING;
    const y = 0;

    displayList.length = 0;
    renderStacks(0, xscale, x, y, places, +1);  // Callees
    renderStacks(0, xscale, x, y-ROW, places, -1);  // Callers (ROW left for separator)
    display(xscale, pos, neg, displayList);
  }

  // renderStacks creates boxes with top-left at x,y with children drawn as
  // nested stacks (below or above based on the sign of direction).