while文を使って、迷路を自動生成したいです。

前提・実現したいこと

ProcessingのPythonモードで、迷路を作成しています。
ｒキーを押した際に、ランダムで迷路の壁が生成される仕組みになっています。
現状ではｒキーを何回か押さなければなりませんが、一度押しただけで迷路内のマス（ｘ、ｙ）のうち、ｘ、ｙがともに偶数であるマスがすべて壁になるまで壁を生成するようにしたいです。
while文の中身のヒントを教えてください。

該当のソースコード

Processing(Python)
1board_x = 0
2board_y = 0
3road_w = 0
4road_map = []
5
6piece_x = 0
7piece_y = 0
8is_playing = False
9is_goal = False
10piece_size = 0
11play_time = 0
12
13dir_x = [1, 0, -1, 0]
14dir_y = [0, 1, 0, -1]
15
16def make_board(x, y, w):
17    global board_x, board_y
18    global road_w
19    global road_map
20
21    board_x = x+4
22    board_y = y+4
23    road_w = w
24    road_map = [[0 for i in range(board_y)] for j in range(board_x)]
25
26def init_maze():
27    for x in range(0, board_x, 1):
28        for y in range(0, board_y, 1):
29            road_map[x][y] = 1
30    for x in range(3, board_x-3, 1):
31        for y in range(3, board_y-3, 1):
32            road_map[x][y] = 0
33    
34    global piece_x, piece_y
35    global is_playing
36    global is_goal
37    global piece_size
38    global play_time
39
40    road_map[2][3] = 2
41    road_map[board_x-3][board_y-4] = 3
42    
43    piece_x = 2
44    piece_y = 3
45    is_playing = False
46    is_goal = False
47    piece_size = 0.7 * road_w
48    play_time = 0
49
50def draw_maze():
51    noStroke()
52    background(100)
53    
54    for x in range(2, board_x-2, 1):
55        for y in range(2, board_y-2, 1):
56            if road_map[x][y] == 0:
57                fill(100, 0, 0)
58            elif road_map[x][y] == 1:
59                fill(0, 200, 0)
60            elif road_map[x][y] == 2:
61                fill(200, 200, 0)
62            elif road_map[x][y] == 3:
63                fill(200, 0, 200)
64            
65            rect(road_w*x, road_w*y, road_w, road_w)
66
67def setup():
68    size(800, 600)
69    make_board(13, 9, 46)
70    init_maze()
71
72def draw():
73    draw_maze()
74    
75    draw_piece()
76    
77    if is_playing or is_goal :
78        draw_info()
79    
80    check_finish()
81
82def keyPressed():
83    global piece_x, piece_y
84    global is_playing
85    
86    if key == 'a':
87        generate_maze_up_down()
88    elif key == 'k':
89        is_playing = True
90    elif key == 'i':
91        init_maze()
92    
93    if is_playing :
94        if keyCode == UP and piece_y > 0 and road_map[piece_x][piece_y-1] != 1:
95            piece_y -= 1
96        if keyCode == RIGHT and piece_x < board_x-1 and road_map[piece_x+1][piece_y] != 1:
97            piece_x += 1
98        if keyCode == DOWN and piece_y < board_y-1 and road_map[piece_x][piece_y+1] != 1:
99            piece_y += 1
100        if keyCode == LEFT and piece_x > 0 and road_map[piece_x-1][piece_y] != 1:
101            piece_x -= 1
102    
103    elif key == 'r':
104        generate_maze_random()
105
106def generate_maze_up_down():
107    for x in range(4, board_x-3, 4):
108        for y in range(3, board_y-4):
109            road_map[x][y] = 1
110    for x in range(6, board_x-3, 4):
111        for y in range(board_y-4, 3, -1):
112            road_map[x][y] = 1
113
114def draw_piece():
115    fill(0, 200, 0)
116    ellipse((piece_x+0.5)*road_w, (piece_y+0.5)*road_w, piece_size, piece_size)
117
118def draw_info():
119    global play_time
120    if is_playing :
121        play_time += 1
122    
123    textSize(30)
124    fill(255, 255, 0)
125    text("Time=" + str(play_time), 20, 30)
126
127def check_finish():
128    global is_playing, is_goal
129    if road_map[piece_x][piece_y] == 3:
130        is_playing = False
131        is_goal = True
132
133def generate_maze_random():
134    while road_map[x][y] != 1:
135        for x in range(2, board_x-2, 2):
136            for y in range(2, board_y-2, 2):
137                if road_map[x][y] ==  1:
138                    r = int(random(0, 3))
139                    dx = dir_x[r]
140                    dy = dir_y[r]
141                    if road_map[x+dx*2][y+dy*2] == 0:
142                        road_map[x+dx][y+dy] = 1
143                        road_map[x+dx*2][y+dy*2] =1