Pygame开发问题：重力效果反向，角色向上而非向下移动

问题根源 #

Pygame的坐标系规则和日常直觉相反：屏幕左上角是坐标原点(0,0)，y轴数值越往下越大。你给gravity设了-2，相当于让角色的y坐标每次循环减2，自然就会向上移动。

修复方法 #

直接把重力值改成正数即可：

# 将原来的gravity = -2修改为
gravity = 2

额外优化建议 #

你的代码里有大量冗余内容（比如后面的dt、x/y变量，以及draw()、screen_bound()等未被调用的函数），这些代码不仅没用，还会增加阅读混乱，建议直接删除，只保留主循环相关的有效逻辑。

修正后的完整核心代码如下：

import pygame, sys
from pygame.locals import QUIT

background_colour = (255, 255, 255)
BLUE = (0, 0, 255)
RED = (255, 0, 0)
(width, height) = (800, 400)

window = pygame.display.set_mode((width, height))
clock = pygame.time.Clock()
background = pygame.Surface(window.get_size())
ts, w, h, c1, c2 = 50, *background.get_size(), (128, 128, 128), (64, 64, 64)
tiles = [((x*ts, y*ts, ts, ts), c1 if (x+y) % 2 == 0 else c2) for x in range((w+ts-1)//ts) for y in range((h+ts-1)//ts)]
[pygame.draw.rect(background, color, rect) for rect, color in tiles]

rect = pygame.Rect(0, 0, 20, 20)
rect.center = window.get_rect().center
speed = 3.4
speed2 = 5

# main application loop
run = True
while run:
    gravity = 2  # 改为正数实现向下重力
    clock.tick(100)
    
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    keys = pygame.key.get_pressed()
    rect.x += (keys[pygame.K_d] - keys[pygame.K_a]) * speed
    rect.y += (keys[pygame.K_s] - keys[pygame.K_w]) * speed2
    rect.y += gravity  # 简化写法，效果和rect.y = rect.y + gravity一致
    border_rect = window.get_rect()
    rect.clamp_ip(border_rect)

    window.blit(background, (0, 0))
    pygame.draw.rect(window, (255, 0, 0), rect)
    pygame.display.flip()

pygame.quit()
exit()

内容的提问来源于stack exchange，提问作者Pantherr