pygame-KidsCanCode系列jumpy-part4-彈跳

終於要到彈跳環節了，向上彈跳其實很簡單，按下空格觸發時，只要把y軸速度給一個向上的速度即可。

Player類，新加一個jump()方法：

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

調用該方法，會使方塊具有向上25px的速度，然后由於重力依然在起作用，所以二者結合，就會形成向上彈跳的效果。

然后在main.py中按空格鍵時，調用jump方法，為了更有趣味性，我們多加幾個檔板，而且為了簡化代碼，把檔板的位置及長寬參數，都定義在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

# 檔板列表
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內容如下：

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)

        # 多放幾塊檔板
        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:
                    # 按空格鍵時，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：

基本的彈跳實現了，但是有2個明顯的問題：

1. 可以在空中，不借助任何檔板的情況下，連環跳，這不太合理，比較貼近現實的預期效果應該是，只在在檔板上，才允許起跳，不能憑空跳躍。
2. 向上跳時，如果上方有檔板，永遠不可能跳過檔板，只要一接近檔板，就自動吸附上去了（仔細看gif最后那段跳躍），這個看上去比較奇怪。

原因如下：

問題1，是因為jump方法中未作任何約束，不管什么時候調用，總是能獲取向上的速度，可以改進為：檢測方法是否站在檔板上（仍然通過碰撞檢測，方塊站在檔板上，肯定就發生了碰撞），只有站在檔板上，調用jump時，才能獲取向上的彈跳速度。

問題2，是因為main.py中，一直在檢測碰撞，向上跳的過程中，如果頭頂有檔板，一碰到檔板，代碼邏輯就強制把方塊固定在檔板上了（即：認為方塊落在檔板上了）。改進方法：僅在下降過程中，才做碰撞檢測。

調試后的sprites.py代碼如下：

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)
        # 初始化時，要把Game類的實例傳過來
        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站在檔板上了，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代碼如下：

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()
        # 只有向下落時，才做碰撞檢測(防止向上跳時，被上方檔板自動吸附）
        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: