pygame-KidsCanCode系列jumpy-part4-弹跳

终于要到弹跳环节了，向上弹跳其实很简单，按下空格触发时，只要把y轴速度给一个向上的速度即可。

Player类，新加一个jump()方法：

    def jump(self):
        self.vel.y = -25

调用该方法，会使方块具有向上25px的速度，然后由于重力依然在起作用，所以二者结合，就会形成向上弹跳的效果。

然后在main.py中按空格键时，调用jump方法，为了更有趣味性，我们多加几个档板，而且为了简化代码，把档板的位置及长宽参数，都定义在settings.py中

# game options

SIZE = WIDTH, HEIGHT = 320, 480
FPS = 60
DEBUG = False

TITLE = "Jumpy!"

# Player properties
PLAYER_ACC = 0.6
PLAYER_GRAVITY = 2
PLAYER_FRICTION = -0.06

# 档板列表
PLATFORM_LIST = [(0, HEIGHT - 30, WIDTH, 30),
                 (WIDTH / 2 - 50, HEIGHT * 0.75, 100, 15),
                 (WIDTH * 0.12, HEIGHT * 0.5, 60, 15),
                 (WIDTH * 0.65, 200, 80, 10),
                 (WIDTH * 0.5, 100, 50, 10)]

# define color
BLACK = 0, 0, 0
WHITE = 255, 255, 255
RED = 255, 0, 0
GREEN = 0, 255, 0
BLUE = 0, 0, 255
YELLOW = 255, 255, 0

main.py内容如下：

from part_04.sprites import *
from part_04.settings import *

class Game:

    def __init__(self):
        pg.init()
        pg.mixer.init()
        self.screen = pg.display.set_mode(SIZE)
        pg.display.set_caption(TITLE)
        self.clock = pg.time.Clock()
        self.running = True
        self.playing = False

    def new(self):
        self.all_sprites = pg.sprite.Group()
        self.platforms = pg.sprite.Group()
        self.player = Player(self)
        self.all_sprites.add(self.player)

        # 多放几块档板
        for plat in PLATFORM_LIST:
            p = Platform(*plat)
            self.all_sprites.add(p)
            self.platforms.add(p)

        self.run()

    def run(self):
        self.playing = True
        while self.playing:
            self.clock.tick(FPS)
            self.events()
            self.update()
            self.draw()

    def update(self):
        self.all_sprites.update()
        hits = pg.sprite.spritecollide(self.player, self.platforms, False)
        if hits:
            self.player.pos.y = hits[0].rect.top
            self.player.vel.y = 0

    def events(self):
        for event in pg.event.get():
            if event.type == pg.QUIT:
                if self.playing:
                    self.playing = False
                self.running = False
            if event.type == pg.KEYDOWN:
                if event.key == pg.K_SPACE:
                    # 按空格键时，向上跳
                    self.player.jump()

    def draw(self):
        self.screen.fill(BLACK)
        self.all_sprites.draw(self.screen)
        self.debug()
        pg.display.flip()

    def debug(self):
        if DEBUG:
            font = pg.font.SysFont('Menlo', 25, True)
            pos_txt = font.render(
                'Pos:(' + str(round(self.player.pos.x, 2)) + "," + str(round(self.player.pos.y, 2)) + ")", 1, GREEN)
            vel_txt = font.render(
                'Vel:(' + str(round(self.player.vel.x, 2)) + "," + str(round(self.player.vel.y, 2)) + ")", 1, GREEN)
            acc_txt = font.render(
                'Acc:(' + str(round(self.player.acc.x, 2)) + "," + str(round(self.player.acc.y, 2)) + ")", 1, GREEN)
            self.screen.blit(pos_txt, (20, 10))
            self.screen.blit(vel_txt, (20, 40))
            self.screen.blit(acc_txt, (20, 70))
            pg.draw.line(self.screen, WHITE, (0, HEIGHT / 2), (WIDTH, HEIGHT / 2), 1)
            pg.draw.line(self.screen, WHITE, (WIDTH / 2, 0), (WIDTH / 2, HEIGHT), 1)

    def show_start_screen(self):
        pass

    def show_go_screen(self):
        pass

g = Game()
g.show_start_screen()
while g.running:
    g.new()
    g.show_go_screen()

pg.quit()

效果如下：

基本的弹跳实现了，但是有2个明显的问题：

1. 可以在空中，不借助任何档板的情况下，连环跳，这不太合理，比较贴近现实的预期效果应该是，只在在档板上，才允许起跳，不能凭空跳跃。
2. 向上跳时，如果上方有档板，永远不可能跳过档板，只要一接近档板，就自动吸附上去了（仔细看gif最后那段跳跃），这个看上去比较奇怪。

原因如下：

问题1，是因为jump方法中未作任何约束，不管什么时候调用，总是能获取向上的速度，可以改进为：检测方法是否站在档板上（仍然通过碰撞检测，方块站在档板上，肯定就发生了碰撞），只有站在档板上，调用jump时，才能获取向上的弹跳速度。

问题2，是因为main.py中，一直在检测碰撞，向上跳的过程中，如果头顶有档板，一碰到档板，代码逻辑就强制把方块固定在档板上了（即：认为方块落在档板上了）。改进方法：仅在下降过程中，才做碰撞检测。

调试后的sprites.py代码如下：

from part_04.settings import *
import pygame as pg
import math

vec = pg.math.Vector2

class Player(pg.sprite.Sprite):
    def __init__(self, game):
        pg.sprite.Sprite.__init__(self)
        # 初始化时，要把Game类的实例传过来
        self.game = game
        self.image = pg.Surface((30, 30))
        self.image.fill(YELLOW)
        self.rect = self.image.get_rect()
        self.rect.center = WIDTH / 2, HEIGHT / 2
        self.pos = self.rect.center
        self.vel = vec(0, 0)
        self.acc = vec(0, 0)
        self.width = self.rect.width
        self.height = self.rect.height

    def jump(self):
        # 只有碰撞了，才能向上跳（即：只有Player站在档板上了，才能起跳）
        hits = pg.sprite.spritecollide(self, self.game.platforms, False)
        if hits:
            self.vel.y = -22

    def update(self):
        self.acc = vec(0, PLAYER_GRAVITY)
        keys = pg.key.get_pressed()
        if keys[pg.K_LEFT]:
            self.acc.x = -PLAYER_ACC
        if keys[pg.K_RIGHT]:
            self.acc.x = PLAYER_ACC

        self.acc.x += self.vel.x * PLAYER_FRICTION

        self.vel += self.acc
        self.pos += self.vel

        if self.rect.left > WIDTH:
            self.pos.x = 0 - self.width / 2
        if self.rect.right < 0:
            self.pos.x = WIDTH + self.width / 2

        #
        if math.fabs(self.rect.bottom - self.pos.y) >= 1:
            self.rect.bottom = self.pos.y
        self.rect.x = self.pos.x - self.width / 2

class Platform(pg.sprite.Sprite):
    def __init__(self, x, y, w, h):
        pg.sprite.Sprite.__init__(self)
        self.image = pg.Surface((w, h))
        self.image.fill(GREEN)
        self.rect = self.image.get_rect()
        self.rect.x = x
        self.rect.y = y

main.py代码如下：

from part_04.sprites import *
from part_04.settings import *

class Game:

    def __init__(self):
        pg.init()
        pg.mixer.init()
        self.screen = pg.display.set_mode(SIZE)
        pg.display.set_caption(TITLE)
        self.clock = pg.time.Clock()
        self.running = True
        self.playing = False

    def new(self):
        self.all_sprites = pg.sprite.Group()
        self.platforms = pg.sprite.Group()
        self.player = Player(self)
        self.all_sprites.add(self.player)

        for plat in PLATFORM_LIST:
            p = Platform(*plat)
            self.all_sprites.add(p)
            self.platforms.add(p)

        self.run()

    def run(self):
        self.playing = True
        while self.playing:
            self.clock.tick(FPS)
            self.events()
            self.update()
            self.draw()

    def update(self):
        self.all_sprites.update()
        # 只有向下落时，才做碰撞检测(防止向上跳时，被上方档板自动吸附）
        if self.player.vel.y > 0:
            hits = pg.sprite.spritecollide(self.player, self.platforms, False)
            if hits:
                self.player.pos.y = hits[0].rect.top
                self.player.vel.y = 0

    def events(self):
        for event in pg.event.get():
            if event.type == pg.QUIT:
                if self.playing:
                    self.playing = False
                self.running = False
            if event.type == pg.KEYDOWN:
                if event.key == pg.K_SPACE:
                    self.player.jump()

    def draw(self):
        self.screen.fill(BLACK)
        self.all_sprites.draw(self.screen)
        self.debug()
        pg.display.flip()

    def debug(self):
        if DEBUG:
            font = pg.font.SysFont('Menlo', 25, True)
            pos_txt = font.render(
                'Pos:(' + str(round(self.player.pos.x, 2)) + "," + str(round(self.player.pos.y, 2)) + ")", 1, GREEN)
            vel_txt = font.render(
                'Vel:(' + str(round(self.player.vel.x, 2)) + "," + str(round(self.player.vel.y, 2)) + ")", 1, GREEN)
            acc_txt = font.render(
                'Acc:(' + str(round(self.player.acc.x, 2)) + "," + str(round(self.player.acc.y, 2)) + ")", 1, GREEN)
            self.screen.blit(pos_txt, (20, 10))
            self.screen.blit(vel_txt, (20, 40))
            self.screen.blit(acc_txt, (20, 70))
            pg.draw.line(self.screen, WHITE, (0, HEIGHT / 2), (WIDTH, HEIGHT / 2), 1)
            pg.draw.line(self.screen, WHITE, (WIDTH / 2, 0), (WIDTH / 2, HEIGHT), 1)

    def show_start_screen(self):
        pass

    def show_go_screen(self):
        pass

g = Game()
g.show_start_screen()
while g.running:
    g.new()
    g.show_go_screen()

pg.quit()

效果如下: