? gray : black;
    colors.push(color);
    colors.push(color);
    colors.push(color);
    colors.push(color);
  }

  return {
    position: positions,
    color: colors,
  };
}

function createNormalLines(vertices) {
  var scale = 10;
  var srcPositions = vertices.position;
  var srcNormals = vertices.normal;

  const normVertices = [];

  for (var ii = 0; ii < srcPositions.length; ii += 3) {
    const cube = twgl.primitives.createCubeVertices(1);
    delete cube.normal;
    delete cube.texcoord;
    cube