Why is this small (155 lines-long) Pacman game on Python running so slow?

Question

I have already cut everything I could from the main loop. I also optimized collisions for dynamic and static objects, reducing considerably the number of iterations. But it is still slow on his machine. I'll post the entire file for the case someone wants to test it, but you can just jump to the main loop at "while Exit==false:".

import pygame
from pyeuclid import Vector2
from math import sin,cos,pi
from random import random

class Thing:
    def __init__(self,pos):
        self.pos = pos
        things.append(self)
    def update(self): pass
    def draw(self,img): pass
    def collide(self,who): pass

class DynamicThing(Thing):
    def __init__(self,pos):
        Thing.__init__(self,pos)
        self.vel = Vector2(0,0)
        self.lastPos = pos
        self.col = (255,255,0)
        self.r = 12
        dynamic_things.append(self)
    def update(self):
        self.lastPos = self.pos
        self.pos = self.pos + self.vel
    def draw(self,img):
        pygame.draw.circle(img, (0,0,0), [int(n) for n in self.pos], self.r, self.r)
        pygame.draw.circle(img, self.col, [int(n) for n in self.pos], self.r-2, self.r-2)
    def collide(self,obj):
        Thing.collide(self,obj)
        if isinstance(obj,Wall): 
            self.pos = self.lastPos

class Wall(Thing):
    def draw(self,img):
        x,y = self.pos.x, self.pos.y
        pygame.draw.rect(img, (90,90,200), (x-16,y-16,32,32), 0)

class Pacman(DynamicThing):
    def __init__(self):
        DynamicThing.__init__(self,Vector2(32*9+16,32*12+16))
        self.col = (255,255,0)
    def update(self):
        DynamicThing.update(self)
        if (keyPressed[pygame.K_LEFT]): self.vel.x = -1
        if (keyPressed[pygame.K_RIGHT]): self.vel.x = 1
        if (keyPressed[pygame.K_DOWN]): self.vel.y = 1
        if (keyPressed[pygame.K_UP]): self.vel.y = -1
        if (self.vel.x==-1 and not keyPressed[pygame.K_LEFT]): self.vel.x = 0
        if (self.vel.x==1 and not keyPressed[pygame.K_RIGHT]): self.vel.x = 0
        if (self.vel.y==1 and not keyPressed[pygame.K_DOWN]): self.vel.y = 0
        if (self.vel.y==-1 and not keyPressed[pygame.K_UP]): self.vel.y = 0
    def collide(self,obj):
        DynamicThing.collide(self,obj)
        if isinstance(obj,Ghost):
            self.pos = Vector2(32*9+16,32*12+16)

class Ghost(DynamicThing):
    def __init__(self):
        DynamicThing.__init__(self,Vector2(32*9+16,32*10+16))
        self.col = (int(random()*255),int(random()*255),int(random()*255))
        self.vel = Vector2(0,-2)
    def update(self):
        DynamicThing.update(self)
        if random()<0.01:
            self.vel = [Vector2(2,0),Vector2(-2,0),Vector2(0,2),Vector2(0,-2)][int(random()*4)]
    def collide(self,obj):
        DynamicThing.collide(self,obj)
        if isinstance(obj,Wall):
            self.vel = [Vector2(2,0),Vector2(-2,0),Vector2(0,2),Vector2(0,-2)][int(random()*4)]

def thingAtPos(pos):
    tile_pos = Vector2(int(pos.x/32),int(pos.y/32))
    return map[tile_pos.y][tile_pos.x]

# initializate stuff
pygame.init()
clock = pygame.time.Clock()
screen = pygame.display.set_mode([32*19,32*22])
points_in_unit_circle_border = [Vector2(cos(float(a)/8*2*pi),sin(float(a)/8*2*pi)) for a in xrange(8)]
things = []
dynamic_things = []
exit = False

map =  [[1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1],
        [1,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,1],
        [1,0,1,1,0,1,1,1,0,1,0,1,1,1,0,1,1,0,1],
        [1,0,1,1,0,1,1,1,0,1,0,1,1,1,0,1,1,0,1],
        [1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1],
        [1,0,1,1,0,1,0,1,1,1,1,1,0,1,0,1,1,0,1],
        [1,0,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,0,1],
        [1,1,1,1,0,1,1,1,0,1,0,1,1,1,0,1,1,1,1],
        [1,1,1,1,0,1,0,0,0,0,0,0,0,1,0,1,1,1,1],
        [1,1,1,1,0,1,0,1,1,0,1,1,0,1,0,1,1,1,1],
        [1,0,0,0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,1],
        [1,1,1,1,0,1,0,1,1,1,1,1,0,1,0,1,1,1,1],
        [1,1,1,1,0,1,0,0,0,0,0,0,0,1,0,1,1,1,1],
        [1,1,1,1,0,1,0,1,1,1,1,1,0,1,0,1,1,1,1],
        [1,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,1],
        [1,0,1,1,0,1,1,1,0,1,0,1,1,1,0,1,1,0,1],
        [1,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,1],
        [1,1,0,1,0,1,0,1,1,1,1,1,0,1,0,1,0,1,1],
        [1,0,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,0,1],
        [1,0,1,1,1,1,1,1,0,1,0,1,1,1,1,1,0,0,1],
        [1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1],
        [1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1]]


#create pacman, walls, ghosts
pacman = Pacman()
for y in xrange(len(map)):
    for x in xrange(len(map[y])):
        if (map[y][x]==1):
            map[y][x] = Wall(Vector2(x*32+16,y*32+16))
for i in xrange(4):
    Ghost()

while exit==False:
    clock.tick(45)

    screen.fill([255,255,255])
    keyPressed = pygame.key.get_pressed()

    # events
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            exit = True
        if event.type == pygame.KEYDOWN and event.key == pygame.K_ESCAPE:
            exit = True

    # more ghosts
    if random()<0.001: Ghost()

    # updates e draws
    for thing in things:
        thing.update()
        thing.draw(screen)

    # collisions
    for A in dynamic_things:
        #dynamic vs dynamic
        for B in dynamic_things:
            if A!=B and abs(A.pos-B.pos)<(A.r+B.r):
                A.collide(B)
                B.collide(A)
        #dynamic vs walls
        for circle_point in points_in_unit_circle_border:
            thing_in_a_border = thingAtPos(A.pos+circle_point*12)
            if isinstance(thing_in_a_border,Wall):
                A.collide(thing_in_a_border)

    pygame.display.flip()

pygame.quit ()

Have you tried to profile the code to see where the bottleneck is occurring? — Levon, Apr 30 '12 at 05:58
Unrelated to the question, I just noted some other thing in the code you should be aware of: Under "# more ghosts" you *should not* use unbounded randomness in a game. Define a randomized interval (eg. 10-30 seconds) between each ghost spawn instead. — Deestan, Apr 30 '12 at 06:01
Levon, how? Ignacio, can you elaborate this and propose an alternative? Deestan sure, thanks. — MaiaVictor, Apr 30 '12 at 06:07
Take a look at these links to get started: http://stackoverflow.com/q/582336/1209279 and http://docs.python.org/library/profile.html. This way you can concentrate your efforts on the code that will yield the most potential speedup. — Levon, Apr 30 '12 at 06:16

score 2 · Accepted Answer · answered May 04 '12 at 16:14

You are redrawing and fliping the whole screen in every loop. I didn't test your program, but on the pacman I know, there are only 5 moving sprites on the screen, you should try to only blit those every frame (and of course if something else changes, that too). And don't display.flip(), just update the areas of the screen that you changed (that normally speeds up a lot).

Of course you need to stop blanking the screen every frame for that, and there will be much management of what to update. There is some extra support for dirty sprites in pygame http://www.pygame.org/docs/ref/sprite.html#pygame.sprite.DirtySprite that help you with that. Or you could maybe just update all 'active' sprites by blanking the position they where and redrawing them in the new position (and obviously everything that also is in those two areas). Collect the effected rects in a list and pass that to update_rects() instead of flipping the screen. There should be no need in drawing the walls in a pacman game in every frame...

score 0 · Answer 2 · answered Apr 30 '12 at 18:50

0

Probably not a big source of slowness, but "while exit==False:" requires a little more bytecode to execute than "while not exit:".

answered Apr 30 '12 at 18:50

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Why is this small (155 lines-long) Pacman game on Python running so slow?

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