Pygame Random Terrain Movement

Question

I'm trying to create a game in which there are rocks on the screen that move when the player moves, as the player is centered in the screen, and instead of the player moving, the terrain does. The problem that I have is that whenever a key is pressed down, about only half of the rocks shift up 2 more pixels, and when released, they go back to the original state. Here is the code for the player update function that controls the movement of terrain, where obx and oby are the coordinates added onto the terrain when moving:

    if forward == True:
        grassx += 2
        obx += 2
        self.forward_walk += 1
        if 15 >= self.forward_walk >= 0:
            self.image = pygame.image.load("person_left_walk_1.png")
        if 30 >= self.forward_walk >= 15:
            self.image = pygame.image.load("person_left_walk_2.png")
        if self.forward_walk >= 30:
            self.forward_walk = 0
    if back == True:
        grassx -= 2
        obx -= 2
        self.backward_walk += 1
        if 15 >= self.backward_walk >= 0:
            self.image = pygame.image.load("person_right_walk_1.png")
        if 30 >= self.backward_walk >= 15:
            self.image = pygame.image.load("person_right_walk_2.png")
        if self.backward_walk >= 30:
            self.backward_walk = 0
    if up == True:
        grassy += 2
        oby += 2
        self.up_walk += 1
        if 15 >= self.up_walk >= 0:
            self.image = pygame.image.load("person_back_walk_1.png")
        if 30 >= self.up_walk >= 15:
            self.image = pygame.image.load("person_back_walk_2.png")
        if self.up_walk >= 30:
            self.up_walk = 0
    if down == True:
        grassy -= 2
        oby -= 2
        self.down_walk += 1
        if 15 >= self.down_walk >= 0:
            self.image = pygame.image.load("person_down_walk_1.png")
        if 30 >= self.down_walk >= 15:
            self.image = pygame.image.load("person_down_walk_2.png")
        if self.down_walk >= 30:
            self.down_walk = 0

This is the rock class, it uses the obx and oby from the previous function (they are global variables):

class Obstacle(pygame.sprite.Sprite):
original_x = 0
original_y = 0
def __init__(self,image,x,y):
    pygame.sprite.Sprite.__init__(self)
    self.image = pygame.image.load(image)
    self.rect = self.image.get_rect()
    self.rect.x = x
    self.rect.y = y
    self.original_x = self.rect.x
    self.original_y = self.rect.y
    self.mask = pygame.mask.from_surface(self.image)

def update(self):
    self.rect.x = self.original_x + obx
    self.rect.y = self.original_y + oby

Ask me if you need any further information. Thanks!

Where do the variables oby and obx come from in the Obstacle.update function? It appears to me that they are never initialized, unless they are globals. — Anthony
– Anthony, Commented Apr 10, 2015 at 22:17
Oh sorry. Perhaps you should make them local at least for the update function. Try def update(obx,oby) then calling update each time you want to change the coordinates. For instance: if up == True: oby+=1 Obstacle_instance.update(0,oby). — Anthony
– Anthony, Commented Apr 10, 2015 at 22:22
Thanks! You solved the problem, something so simple that I never even thought of. Post it as an answer, I'll mark it as correct. — Bagel
– Bagel, Commented Apr 10, 2015 at 22:36

Anthony · Accepted Answer · 2015-04-10 22:51:47Z

1

You need to make the variables obx and oby local variables, at least in the update function. They you need to call the update function each time you want to move the obstacles.

class Obstacle...
...
    def update(self, obx, oby):
        ...

and then

if forward == True:
    grassx += 2
    obx += 2
    Obstacle_instance.update(obx,0)
        ...

etc.

Im sorry I can't provide an in depth explanation of why this is the case, but my guess is that your main problem was the placement of the update function. My guess is that the update function would update it, then the global variable would change back and the update function would shift the objects accordingly.

answered Apr 10, 2015 at 22:51

Anthony

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