Implementing the game logic

Now that we've built all the components required to make an implementation of the 2048 game, let's move on to more interesting things: spawning, moving, and combining tiles.

It's only logical that we begin with spawning new tiles in random empty cells. The algorithm for doing so is as follows:

1. Find all cells that are currently empty.

2. Pick a random one from those found in step 1.

3. Create a new tile at the position determined in step 2.

4. Add it to the internal grid (Board.b), and to the board widget itself (using add_widget()) for Kivy to render it.

The sequence of actions should be self-evident; the following Python implementation of this algorithm is also very straightforward:

# In main.py, a method of class Board:
def new_tile(self, *args):
    empty_cells = [(x, y) for x, y in all_cells()  # Step 1
                   if self.b[x][y] is None]

    x, y = random.choice(empty_cells)  # Step 2
    tile = Tile(pos=self.cell_pos(x, y),  # Step 3
                size=self.cell_size...