Python 游戏中的重力

我正在用pygame制作一个平台游戏，我想给它添加重力。 现在我只有一张当我按下箭头键时会移动的图片，下一步就是重力。这是我的密码：

import pygame, sys
from pygame.locals import *

pygame.init()

FPS = 30
fpsClock = pygame.time.Clock()

DISPLAYSURF = pygame.display.set_mode((400, 300), 0, 32)
pygame.display.set_caption("Jadatja")

WHITE = (255, 255, 255)
catImg = pygame.image.load("images/cat.png")
catx = 10
caty = 10
movingRight = False
movingDown = False
movingLeft = False
movingUp = False

while True: #main game loop

    #update
    for event in pygame.event.get():
    if event.type == KEYDOWN:
        if event.key == K_RIGHT:
            #catx += 5
            movingRight = True
            movingLeft = False
        elif event.key == K_DOWN:
            #caty += 5
            movingDown = True
            movingUp = False
        elif event.key == K_LEFT:
            #catx -= 5
            movingLeft = True
            movingRight = False
        elif event.key == K_UP:
            #caty -= 5
            movingUp = True
            movingDown = False

    if event.type == KEYUP:
        if event.key == K_RIGHT:
            movingRight = False
        if event.key == K_DOWN:
            movingDown = False
        if event.key == K_LEFT:
            movingLeft = False
        if event.key == K_UP:
            movingUp = False


    #actually make the player move
    if movingRight == True:
        catx += 5
    if movingDown == True:
        caty += 5
    if movingLeft == True:
        catx -= 5
    if movingUp == True:
        caty -= 5


    #exit
    for event in pygame.event.get():
        if event.type == KEYUP:
            if event.key == K_ESCAPE:
                pygame.quit()
                sys.exit()

        if event.type == QUIT:
            pygame.quit()
            sys.exit()

    #draw
    DISPLAYSURF.fill(WHITE)
    DISPLAYSURF.blit(catImg, (catx, caty))



    pygame.display.update()
    fpsClock.tick(FPS)

我不是100%确定这段代码是否像我想的那样流畅，但我希望你们能有所收获

谢谢你制作了一个弹跳球，我想这可能对你有帮助

现在，要将重力添加到该模拟中，只需在每次通过回路时在y方向上添加一些额外的速度：

speed[1] += gravity

然而，你最终得到的是一种傻傻的感觉，因为图像很快下降到窗口底部以下，再也看不见：）

因此，下一步是剪裁球的位置，使其必须保持在窗口中：

import os
import sys, pygame
pygame.init()

size = width, height = 320, 240
speed = [1, 1]
black = 0, 0, 0
gravity = 0.1

screen = pygame.display.set_mode(size)

image_file = os.path.expanduser("~/pybin/pygame_examples/data/ball.png")
ball = pygame.image.load(image_file)
ballrect = ball.get_rect()

def clip(val, minval, maxval):
    return min(max(val, minval), maxval)

while 1:
    for event in pygame.event.get():
        if event.type == pygame.QUIT: sys.exit()

    speed[1] += gravity

    ballrect = ballrect.move(speed)
    if ballrect.left < 0 or ballrect.right > width:
        speed[0] = -speed[0]
    if ballrect.top < 0 or ballrect.bottom > height:
        speed[1] = -speed[1]

    # clip the position to remain in the window

    ballrect.left = clip(ballrect.left, 0, width)
    ballrect.right = clip(ballrect.right, 0, width)        
    ballrect.top = clip(ballrect.top, 0, height)
    ballrect.bottom = clip(ballrect.bottom, 0, height) 

    screen.fill(black)
    screen.blit(ball, ballrect)
    pygame.display.flip()

您可以将其改写为如下内容：

delta = {
    pygame.K_LEFT: (-20, 0),
    pygame.K_RIGHT: (+20, 0),
    pygame.K_UP: (0, -20),
    pygame.K_DOWN: (0, +20),  
    }
for event in pygame.event.get():
    if event.type == pygame.KEYDOWN:
        deltax, deltay = delta.get(event.key, (0, 0))
        ball.speed[0] += deltax
        ball.speed[1] += deltay

您还可以将与图像移动相关的所有逻辑放入一个类中：

class Ball(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self) 
        self.image = pygame.image.load(image_file)
        self.rect = self.image.get_rect()
        self.speed = [0, 0]
        area = pygame.display.get_surface().get_rect()
        self.width, self.height = area.width, area.height

    def update(self):
        self.rect = self.rect.move(self.speed)
        if self.rect.left < 0 or self.rect.right > self.width:
            self.speed[0] = -self.speed[0]
        if self.rect.top < 0 or self.rect.bottom > self.height:
            self.speed[1] = -self.speed[1]
        self.rect.left = clip(self.rect.left, 0, self.width)
        self.rect.right = clip(self.rect.right, 0, self.width)        
        self.rect.top = clip(self.rect.top, 0, self.height)
        self.rect.bottom = clip(self.rect.bottom, 0, self.height)                

---

到目前为止，你尝试了什么来实现重力？当精灵被认为“在空中”时，重力的“你好世界”通过应用负caty来工作。但我重申，到目前为止，你做了哪些尝试？

class Ball(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self) 
        self.image = pygame.image.load(image_file)
        self.rect = self.image.get_rect()
        self.speed = [0, 0]
        area = pygame.display.get_surface().get_rect()
        self.width, self.height = area.width, area.height

    def update(self):
        self.rect = self.rect.move(self.speed)
        if self.rect.left < 0 or self.rect.right > self.width:
            self.speed[0] = -self.speed[0]
        if self.rect.top < 0 or self.rect.bottom > self.height:
            self.speed[1] = -self.speed[1]
        self.rect.left = clip(self.rect.left, 0, self.width)
        self.rect.right = clip(self.rect.right, 0, self.width)        
        self.rect.top = clip(self.rect.top, 0, self.height)
        self.rect.bottom = clip(self.rect.bottom, 0, self.height)                

"""
http://stackoverflow.com/a/15459868/190597 (unutbu)
Based on http://www.pygame.org/docs/tut/intro/intro.html
Draws a red ball bouncing around in the window.
Pressing the arrow keys moves the ball
"""

import sys
import pygame
import os


image_file = os.path.expanduser("~/pybin/pygame_examples/data/ball.png")

delta = {
    pygame.K_LEFT: (-20, 0),
    pygame.K_RIGHT: (+20, 0),
    pygame.K_UP: (0, -20),
    pygame.K_DOWN: (0, +20),  
    }

gravity = +1

class Ball(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self) 
        self.image = pygame.image.load(image_file)
        self.rect = self.image.get_rect()
        self.speed = [0, 0]
        area = pygame.display.get_surface().get_rect()
        self.width, self.height = area.width, area.height

    def update(self):
        self.rect = self.rect.move(self.speed)
        if self.rect.left < 0 or self.rect.right > self.width:
            self.speed[0] = -self.speed[0]
        if self.rect.top < 0 or self.rect.bottom > self.height:
            self.speed[1] = -self.speed[1]
        self.rect.left = clip(self.rect.left, 0, self.width)
        self.rect.right = clip(self.rect.right, 0, self.width)        
        self.rect.top = clip(self.rect.top, 0, self.height)
        self.rect.bottom = clip(self.rect.bottom, 0, self.height)                

def clip(val, minval, maxval):
    return min(max(val, minval), maxval)

class Main(object):
    def __init__(self):
        self.setup()
    def setup(self):
        pygame.init()
        size = (self.width, self.height) = (640,360)
        self.screen = pygame.display.set_mode(size, 0, 32)
        self.ball = Ball()
        self.setup_background()
    def setup_background(self):
        self.background = pygame.Surface(self.screen.get_size())
        self.background = self.background.convert()
        self.background.fill((0, 0, 0))
        self.screen.blit(self.background, (0, 0))
        pygame.display.flip()
    def draw(self):
        self.screen.blit(self.background, (0, 0))
        self.screen.blit(self.ball.image, self.ball.rect)
        pygame.display.flip()
    def event_loop(self):
        ball = self.ball
        friction = 1
        while True:
            for event in pygame.event.get():
                if ((event.type == pygame.QUIT) or 
                    (event.type == pygame.KEYDOWN and 
                     event.key == pygame.K_ESCAPE)):
                    sys.exit()
                elif event.type == pygame.KEYDOWN:
                    deltax, deltay = delta.get(event.key, (0, 0))
                    ball.speed[0] += deltax
                    ball.speed[1] += deltay
                    friction = 1
                elif event.type == pygame.KEYUP:
                    friction = 0.99

            ball.speed = [friction*s for s in ball.speed]
            ball.speed[1] += gravity
            ball.update()
            self.draw()
            pygame.time.delay(10)

if __name__ == '__main__':
    app = Main()
    app.event_loop()