private void GenerateBlock()
{
_blocks = new Grid<bool>(_gridSize);
_blocks.SetEach(
( block, point ) =>
!_paths[ point ] &&
( _trees[ point ] != '.'
|| _walls[ point ]
|| _rivers[ point ] )
);
var blocks = new Grid<byte>(_gridSize);
blocks.SetEach(
(value, point) =>
(byte)(_blocks[point] ? 0 : 255)
);
File.WriteAllText( "blocks.pgm", blocks.ToPgm() );
}