tices);
  var colors = twgl.primitives.createAugmentedTypedArray(4, numVertices);

  //  ..|..|..|..
  //  <-  size ->
  var black = [0, 0, 0, 1];
  var gray = [0.75, 0.75, 0.75, 1];

  var gridSize = size / (subdivisions + 2);
  for (var ii = 0; ii < numLines; ++ii) {
    var jj = ii - ((numLines - 1) / 2);
    var p = jj * gridSize;
    positions.push([p, 0, -size / 2]);
    positions.push([p, 0,  size / 2]);
    positions.push([-size / 2, 0, p]);
    positions.push([ size / 2, 0, p]);
    var color = jj 