Mathematica code:

S[x_, y_, w_, a_, t_] := 
 Sin[w ((Cos[a] + Sin[a]) x + (Sin[a] - Cos[a]) y) + t*2 Pi]

G[N_, t_,] :=
 Graphics[
  Table[
   Disk[
    {x, y},
    .55*(1 + Sum[S[x, y, w, a*2 Pi/N, t], {a, 0, N - 1, 1}]/(2 N))],
   {x, -25, 25, 1}, {y, -25, 25, 1}],
  PlotRange -> 25.85, ImageSize -> 500]

Manipulate[
G[N,t],
 {N,{5,7,9,11}}, {t, 0, .95, .05}]