Pygame中方向相反时，玩家移动停止

Question

I am messing around with pygame and I am eventually working towards a pong clone. I implemented player movement with the arrow keys and when ever I switch from going up to immediately going down, my player freezes and won't move again until I press that direction key again. Here is my code:

import sys, pygame

pygame.init()

display_width = 640
display_height = 480

display = pygame.display.set_mode((display_width,display_height))
pygame.display.set_caption("Test Game")

black = (0,0,0)
white = (255,255,255)

clock = pygame.time.Clock()

running = True

class Player:

    def __init__(self,x,y,hspd,vspd,color,screen):
        self.x = x
        self.y = y
        self.hspd = hspd
        self.vspd = vspd
        self.color = color
        self.screen = screen

    def draw(self):
        pygame.draw.rect(self.screen,self.color,(self.x,self.y,32,32))

    def move(self):
        self.x += self.hspd
        self.y += self.vspd

player = Player(0,0,0,0,black,display)

while running:

    clock.tick(60)

    for event in pygame.event.get():

        if event.type == pygame.QUIT:
            running = False

        if event.type == pygame.KEYUP:
            if event.key == pygame.K_RIGHT:
                player.hspd = 0
            if event.key == pygame.K_LEFT:
                    player.hspd = 0
            if event.key == pygame.K_UP:
                player.vspd = 0
            if event.key == pygame.K_DOWN:
                player.vspd = 0

        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_RIGHT:
                player.hspd = 4
            if event.key == pygame.K_LEFT:
                player.hspd = -4
            if event.key == pygame.K_UP:
                player.vspd = -4
            if event.key == pygame.K_DOWN:
                player.vspd = 4


    #Clear the screen
    display.fill(white)

    #Move objects
    player.move()
    #Draw objects
    player.draw()

    #Update the screen
    pygame.display.flip()

print "I made it!"
pygame.quit()
sys.exit()

Answer 1

I suggest you work with key.get_pressed() to check for the current set of pressed keys.

In your scenario - when you press down and release up (in that order) - the speed is set to 0, so you need to inspect the keys pressed not just by the current event.

Here is a working version of the relevant part:

def current_speed():
    # uses the fact that true = 1 and false = 0
    currently_pressed = pygame.key.get_pressed()
    hdir = currently_pressed[pygame.K_RIGHT] - currently_pressed[pygame.K_LEFT]
    vdir = currently_pressed[pygame.K_DOWN] - currently_pressed[pygame.K_UP]
    return hdir * 4, vdir * 4

while running:

    clock.tick(60)

    for event in pygame.event.get():

        if event.type == pygame.QUIT:
            running = False

        player.hspd, player.vspd = current_speed()

    #Clear the screen
    display.fill(white)

    #Move objects
    player.move()
    #Draw objects
    player.draw()

    #Update the screen
    pygame.display.flip()

Answer 2

your problem is here:

if event.type == pygame.KEYUP:
        if event.key == pygame.K_RIGHT:
            player.hspd = 0
        if event.key == pygame.K_LEFT:
                player.hspd = 0
        if event.key == pygame.K_UP:
            player.vspd = 0
        if event.key == pygame.K_DOWN:
            player.vspd = 0

if event.type == pygame.KEYDOWN:
        if event.key == pygame.K_RIGHT:
            player.hspd = 4
        if event.key == pygame.K_LEFT:
            player.hspd = -4
        if event.key == pygame.K_UP:
            player.vspd = -4
        if event.key == pygame.K_DOWN:
            player.vspd = 4  

I am guessing that your key event down is still consumed when u switch the keys immediately, meaning no other key down event is getting triggered as long as the first event didn't fire its key up event yet.

EDIT: maybe its better to check if the player is moving and if so just reverse speed . Then you would only need to check the down event. Otherwise your event will be consumed and not checked properly. For your method you would need to store the occurred key events since the last frame and check that list.

Answer 3

To expand on LPK's answer, your key down (for event.key == pygame.K_DOWN) is likely being processed before your key up (from event.key == pygame.K_UP) is processed. So while both are down (and you can confirm this), you may experience movement, until you release the up key.