多年前写过一篇 Flash/Flex学习笔记(25)：摩擦力与屏幕环绕，可惜的当时上传的flash，服务器后来无人维护，现在flash链接都失效了。本篇用pygame重新实现了一个：
原理是类似，但要注意的是：pygame中旋转的角度采用逆时针系统 ，即：逆时针方向旋转，角度为正，反之为负。所以在外理角度时，y轴方向的速度要取反。
素材图（2张）：
飞船熄火
飞船点火
需求：按向上键点火，飞船启动，一直加速；无按键时，飞船熄火，速度慢慢降下来（设置摩擦系数）；左右键控制转向；飞出屏幕时，从另一侧切回来。
代码：
import os
import pygame
import sys
import math pygame.init() clock = pygame.time.Clock() SIZE = WIDTH, HEIGHT = 400, 400
GRAY = (200, 200, 200)
RED = (255, 0, 0)
screen = pygame.display.set_mode(SIZE)
pygame.display.set_caption("ship")
img_base_path = os.getcwd() + '/img/' class Ship(object):
def __init__(self, img_base_path, screen):
self.vx = 0
self.vy = 0
# 旋转角速度
self.vr = 0
# 推进力
self.thrust = 0
self.angle = 0
self.show_flame = False
self.scale = 1.0
# 是否显示辅助边框
self.show_rect = False self.img_src = pygame.image.load(img_base_path + 'ship.png')
self.img_flame_src = pygame.image.load(img_base_path + 'ship_flame.png') self.img = self.img_src
self.rect = self.img_src.get_rect() self.img_new = self.img
self.rect_new = self.img_new.get_rect() self.rect = self.rect.move((WIDTH - self.rect.width) * 0.5, (HEIGHT - self.rect.height) * 0.5) def draw(self, screen):
screen.blit(self.img_new, self.rect_new)
if self.show_rect:
pygame.draw.rect(screen, GRAY, ship.rect, 1)
pygame.draw.rect(screen, RED, ship.rect_new, 1) def move(self):
self.rect = self.rect.move(self.vx, self.vy)
self.rect_new = self.rect_new.move(self.vx, self.vy)
# 向左飞出边界
if self.rect_new.right < 0 and ship.vx < 0:
self.rect_new.left = WIDTH
self.rect.left = WIDTH
# 向右飞出边界
if self.rect_new.left > WIDTH and ship.vx > 0:
self.rect_new.right = 0
self.rect.right = 0
# 向下飞出边界
if self.rect_new.top > HEIGHT and ship.vy > 0:
self.rect_new.bottom = 0
self.rect.bottom = 0
# 向上飞出边界
if self.rect_new.bottom < 0 and ship.vy < 0:
self.rect_new.top = HEIGHT
self.rect.top = HEIGHT def rotate_zoom(self):
# rotozoom=旋转+缩放
self.img_new = pygame.transform.rotozoom(self.img, self.angle, self.scale)
self.rect_new = self.img_new.get_rect(center=self.rect.center)
if math.fabs(self.angle) == 360:
self.angle = 0 def set_flame(self, show_flame=False):
self.show_flame = show_flame
if self.show_flame:
self.img = self.img_flame_src
else:
self.img = self.img_src def get_speed(speed):
if speed > 0:
return math.ceil(speed)
if speed < 0:
return math.floor(speed)
return speed ship = Ship(img_base_path, screen)
ship.scale = 0.5
ship.show_rect = True
# 摩擦系数
friction = 0.995
while True:
clock.tick(60) for event in pygame.event.get():
if event.type == pygame.QUIT:
sys.exit()
elif event.type == pygame.KEYUP:
# KEYUP时，熄火，动力归0
ship.vr = 0
ship.thrust = 0
ship.set_flame(False)
elif event.type == pygame.KEYDOWN:
keys = pygame.key.get_pressed()
if keys[pygame.K_LEFT]:
ship.vr = 5
elif keys[pygame.K_RIGHT]:
ship.vr = -5
if keys[pygame.K_UP]:
# 按向上键时，点火，动力为0.3
ship.set_flame(True)
ship.thrust = 0.3
else:
ship.set_flame(False) # 将每一帧的底色先填充成白色
screen.fill((255, 255, 255)) pygame.draw.line(screen, GRAY, (0, HEIGHT / 2), (WIDTH, HEIGHT / 2), 1)
pygame.draw.line(screen, GRAY, (WIDTH / 2, 0), (WIDTH / 2, HEIGHT), 1) ship.angle += ship.vr
ax = math.cos(ship.angle * math.pi / 180) * ship.thrust
# 注：pygame中，角度是逆时针转的，所以垂直加速度要取反
ay = -1 * math.sin(ship.angle * math.pi / 180) * ship.thrust
ship.vx += ax
ship.vy += ay # 摩擦系数
if math.fabs(ship.vx) > 0.001:
ship.vx = ship.vx * friction
if math.fabs(ship.vy) > 0.001:
ship.vy = ship.vy * friction print("vx:", ship.vx) ship.rotate_zoom()
ship.move()
ship.draw(screen) # 更新画布
pygame.display.update()
如果把背景变成黑色，辅助边框去掉，看上去更有漆黑宇宙的感觉:)
源代码地址： https://github.com/yjmyzz/pygame_tutorial/blob/master/move_02.py