pygame - on hold button down

问题:

I found a solution to make a sprite move when you hold a key down. The problem is that it forces writing ugly duplicated code. The current solution I found is:

       for event in pygame.event.get():
            if event.type == KEYDOWN:
                keystate = pygame.key.get_pressed()
                while keystate[K_RIGHT]:
                    screen.fill((255,255,255))
                    pygame.event.get()

                    for sprite in sprites:
                        rimage = sprite[1].getimage()

                        if sprite[2] is None:
                            x+=3
                            sprite[1].update(time)
                            screen.blit(rimage, (x,y))
                            if sprite[1].isfinished() == True:
                                sprite[1].reset()
                            last_dir = "right"
                            if x >= screen_width - rimage.get_width():
                                x = screen_width - rimage.get_width()

                    #update player sprite movement
                    #update player sprite animation
                    #update rest of game map

                    keystate = pygame.key.get_pressed()
                    time = pygame.time.get_ticks()


                    pygame.display.update()

The problem is that the while keystate block. It has to be repeated for each direction and the game world needs to be updated in each while block. That is five places where the same code needs to be duplicated....4 directions plus if a key is not pressed. I could wrap it in a function but I was wondering if there was a better way to handle holding down a button in pygame.

回答1:

The usual way program in pygame is use the events to update the direction, then write the update position code outside events, that way you don't need replicated code.

clock = pygame.time.Clock()

direction = (0,0)

while True:    # main loop

   for event in pygame.event.get():

        if event.type == KEYDOWN:
            if event.key == K_RIGHT:
                direction = (3, 0)
            elif event.key == K_LEFT:
                direction = (-3, 0)
            elif event.key == K_UP:
                direction = (0, 3)
            elif event.key == K_DOWN:
                direction = (0, -3)
            else:
                print "Unrecognized key"

        if event.type == KEYUP:
            direction = (0, 0)

    screen.fill((255,255,255))

    for sprite in sprites:
        rimage = sprite[1].getimage()

        if sprite[2] is None:

            # Check if new position is inside the screen
            new_pos = x + direction[0], y + direction[1]
            if new_pos[0] + rimage.get_width() < screen_width:
                x = new_pos[0]
            if new_pos[1] + rimage.get_height() < screen_height:
                y = new_pos[1]

            # Draw the sprite
            sprite[1].update(time)
            screen.blit(rimage, (x,y))
            if sprite[1].isfinished() == True:
                sprite[1].reset()
                last_dir = direction

    #update player sprite movement
    #update player sprite animation
    #update rest of game map

    time = pygame.time.get_ticks()

    pygame.display.update()

    clock.tick(40)  # Keep game running at 40 fps

If you want you can achieve the same with keystate, in such case you don't need to process key events.

回答2:

Pygame suggests or implies the division of programs into 3 parts:

The event handling, updating and drawing. As pmoleri already said, you simply change the direction of the movement. In the update function, you should pass in a delta time parameter, to move all the sprites according to the time passed. It is quite important, since the other technique doesn't take into account the variable speed of the processor. Games in DOS have been made this way, so now we need emulators to artificially slow down the processor. The draw part simply draws all the sprites.

This way you have a clear division between these 3 distinc parts in games: player input, game logic(movement, collision, actions etc.) and drawing.

回答3:

Additionally, pygame.key.get_pressed() can be used.

This returns a list of all the keys currently being held down.

keys = pygame.key.get_pressed()

if keys[pygame.K_w]:
  # Move Up
if keys[pygame.K_a]:
  # Move Down
... etc ...

This does not need to be in the event section, but probably where the player updates.

This can make the code less clunky and (possible) be more efficient

-Hope I helped!