python - pygame ビットマスクの衝突が機能しません

Question

pygame.sprite.collide_rectまたはを使用すると衝突が検出されますがpygame.sprite.collide_circle、ビットマスクをスプライトに割り当てて実行しようとすると、衝突が検出されません。（wall.collision_action()は、最初の円を他の円と同じ速度と方向で移動させます）これは今のところ問題ではありません
が、pygame.sprite.collide_circle を正常に動作させる円の画像を使用しているため、将来的にはより詳細で非円形のスプライトを使用すると、それになります。

コード：

import pygame, sys, math
from pygame.locals import *
pygame.init()

class ball_class(pygame.sprite.Sprite):
    def __init__(self, surface):
        self.surface = surface
        self.x = 250
        self.y = 250
        self.vy = 0
        self.vx = 0
        self.sprite = pygame.sprite.Sprite()
        self.sprite.image = pygame.image.load("ball.png").convert()
        self.sprite.rect = self.sprite.image.get_rect(center = (self.x, self.y))
        self.sprite.rect.topleft = [int(self.x), int(self.y)]
        self.sprite.mask = pygame.mask.from_surface(self.sprite.image)

    def event(self, event):
        if event.key == K_UP:
            self.vy = -1
            self.vx = 0
        elif event.key == K_DOWN:
            self.vy = 1
            self.vx = 0
        elif event.key == K_LEFT:
            self.vx = -1
            self.vy = 0
        elif event.key == K_RIGHT:
            self.vx = 1
            self.vy = 0

    def move(self):
        self.y += self.vy
        self.x += self.vx
        self.sprite.rect.topleft = [int(self.x), int(self.y)]
        self.sprite.mask = pygame.mask.from_surface(self.sprite.image)

    def draw(self, surface):
        surface.blit(self.sprite.image, self.sprite.rect)

    def position(self):
        return self.sprite.rect()

class wall_class(pygame.sprite.Sprite):
    def __init__(self, surface):
        self.surface = surface
        self.x = 250
        self.y = 100
        self.vy = 0
        self.sprite = pygame.sprite.Sprite()
        self.sprite.image = pygame.image.load("ball.png").convert()
        self.sprite.rect = self.sprite.image.get_rect(center = (self.x, self.y))
        self.sprite.rect.topleft = [int(self.x), int(self.y)]
        self.sprite.mask = pygame.mask.from_surface(self.sprite.image)

    def draw(self, surface):
        surface.blit(self.sprite.image, self.sprite.rect)

    def collision_action(self):
        self.vy = ball.vy
        self.vx = ball.vx
        self.x += self.vx
        self.y += self.vy
        self.sprite.rect.topleft = [int(self.x), int(self.y)]

def gameQuit():
    pygame.quit()
    sys.exit()

screen = pygame.display.set_mode((500, 500), 0, 32)
ball = ball_class(screen)
wall = wall_class(screen)
clock = pygame.time.Clock()
while True:
    screen.fill((0, 0, 0))
    ball.move()
    ball.draw(screen)
    wall.draw(screen)
    is_a_collision = pygame.sprite.collide_mask(wall.sprite, ball.sprite)
    if is_a_collision:

        wall.collision_action()

    for event in pygame.event.get():
        if event.type == QUIT:
            gameQuit()
        elif event.type == KEYDOWN:
            ball.event(event)
    clock.tick(100)
    pygame.display.update()