function add_face_x(mesh, x, face){
  const ndx = mesh.vertices.length / 3;
  var [start_greedy, width, start_increment, height] = face;
  mesh.vertices.push(
    x, start_greedy, start_increment,
    x, start_greedy + width + 1, start_increment,
    x, start_greedy , start_increment + height + 1,
    x, start_greedy + width + 1, start_increment + height + 1);
  mesh.normals.push(-1,0,0);
  mesh.uvs.push(x*16*16+start_greedy,start_increment);
  mesh.uvs.push(x*16*16+start_greedy+width+1, start_increment);
  mesh.uvs.push(x*16*16+start_greedy,start_increment + height+1);
  mesh.uvs.push(x*16*16+start_greedy+width+1,start_increment + height+1);
  mesh.indices.push(
    ndx, ndx + 1, ndx + 2,
    ndx + 2, ndx + 1, ndx + 3,
  );
}