Animating 2D cellular automata with the entire grid in sight

Question

In animating a 2D cellular automata like this:

    Animate[ArrayPlot[CellularAutomaton[20, {{1}, 0}, {n, All}], 
  Mesh -> True] , {n, 0, 20, 0}, AnimationRunning -> False]

The animation displays each iteration and the grid is expanding. Is there instead a way to animate the cellular automation while seeing the entire grid at all times? Similar to the point of view in the animation of game of life on Wikipedia.

Answer 1

m = 20;

Animate[ArrayPlot[ArrayPad[CellularAutomaton[20, {{1}, 0}, {n, All}], 
    {{0, m - n}, {m - n, m - n}}], Mesh -> True], 
 {n, 0, m, 1}, AnimationRunning -> False]

Answer 2

You can use PadRight and PadLeft to pad the matrix with zeroes.

One possible solution is

Module[{rule = 20, max = 20, ca},
 ca = CellularAutomaton[rule, {{1}, 0}, {max, All}];
 Animate[
  ArrayPlot[
   (* Display only the first n rows of ca and pad the rest with zeroes *)
   PadRight[ca[[;; n]], {max + 1, 2 max + 1}],
   Mesh -> True
   ], {n, 1, max, 0}, AnimationRunning -> False]
 ]