https://qiita.com/TN0321/items/c2d006c57aa22c5c8bc9#comment-1e5bb6205650025f828e

cannongame.py

import math
import sys
import pygame
from pygame.locals import *
from random import randint
import time

pygame.init()
WIDTH, HEIGHT = 800, 600
screen = pygame.display.set_mode((WIDTH, HEIGHT))
pygame.display.set_caption("Game")
sysfont = pygame.font.SysFont(None, 36)
pygame.key.set_repeat(5, 5)
FPSCLOCK = pygame.time.Clock()
FPS = 15


class Cannon:
    image = pygame.image.load("cannon.png")

    def __init__(self):
        self.radian = 45
        self.bullet = Bullet()

    def up(self):
        if self.radian < 89:
            self.radian += 1

    def down(self):
        if self.radian > 0:
            self.radian -= 1

    def fire(self):
        self.bullet.fire(self.radian)

    def hit(self, target):
        return self.bullet.hit(target)

    def move(self):
        self.bullet.move()

    def draw(self):
        image = pygame.transform.rotate(self.image, self.radian - 45)
        rect = image.get_rect()
        rect.center = (84, 536)
        screen.blit(image, rect)
        self.bullet.draw()


class Bullet:
    image = pygame.image.load("bullet.png")

    def __init__(self):
        self.reset()

    def reset(self):
        self.x = 68
        self.y = HEIGHT - 80
        self.speed = 50
        self.time = 0
        self.fired = False

    def fire(self, radian):
        if not self.fired:
            self.radian = math.radians(radian)
            self.fired = True

    def hit(self, target):
        return self.fired and target.hit(self.x, self.y)

    def move(self):
        if not self.fired:
            return

        gravity = 9.8
        speed_x = self.speed * math.cos(self.radian)
        speed_y = self.speed * math.sin(self.radian)
        self.x = self.x + speed_x
        self.y = self.y - speed_y + gravity * self.time
        self.time += 0.2

        if self.x > WIDTH or self.y > HEIGHT:
            self.reset()

    def draw(self):
        if self.fired:
            screen.blit(self.image, (self.x, self.y))


class Balloon:
    balloon_image = pygame.image.load("balloon-red.png")
    pang_image = pygame.image.load("pang.png")

    def __init__(self):
        self.reset()

    def reset(self):
        self.x = randint(500, 700)
        self.y = 600
        self.create_time = time.time()
        self.hit_time = None
        self.hit_rect = None

    def hit(self, bullet_x, bullet_y):
        if self.hit_time:
            return False
        distance_y = ((self.y + 15) - (bullet_y + 16))**2
        distance_x = ((self.x + 20) - (bullet_x + 16))**2
        distance = (distance_x + distance_y)**(1 / 2)
        if distance > 31:
            return False
        self.hit_rect = self.pang_image.get_rect()
        self.hit_rect.center = (self.x + 20, self.y + 15)
        self.hit_time = time.time()
        return True

    def move(self):
        if self.hit_time:
            now = time.time()
            if now - self.hit_time > 1:
                self.reset()
            return
        self.y -= 12
        if time.time() - self.create_time > 4:
            self.reset()

    def draw(self):
        if self.hit_rect:
            screen.blit(self.pang_image, self.hit_rect)
        else:
            screen.blit(self.balloon_image, (self.x, self.y))


class CannonGame:

    def __init__(self):
        self.cannon = Cannon()
        self.balloon = Balloon()
        self.score = 0

    def play(self):
        while True:
            self.event()
            self.move()
            if self.cannon.hit(self.balloon):
                self.score += 100
            self.draw()
            FPSCLOCK.tick(FPS)

    def event(self):
        for event in pygame.event.get():
            if event.type == QUIT:
                pygame.quit()
                exit(0)
            if event.type != KEYDOWN:
                return
            if event.key == K_SPACE:
                self.cannon.fire()
            elif event.key == K_UP:
                self.cannon.up()
            elif event.key == K_DOWN:
                self.cannon.down()

    def move(self):
        self.cannon.move()
        self.balloon.move()

    def draw(self):
        screen.fill((255, 255, 255))
        self.cannon.draw()
        self.balloon.draw()
        score_image = sysfont.render(f"score : {self.score}", True, (0, 0, 255))
        screen.blit(score_image, (10, 20))
        pygame.display.update()

if __name__ == '__main__':
    CannonGame().play()