Python Recursion Function Causes Pygame to Freeze

Question

I have a really complex mock paint program in python that is roughly 350 lines long. However, when I use my fill bucket tool it fills the shape I've drawn and then freezes the Pygame Window no matter the size of the shape. I can still move the mouse and the window, and the title does NOT change to "Not responding." But when my mouse hovers over the window, the cursor changes to the spinning wheel.

My fill bucket tool is a recursion program that flood fills the surrounding pixels and stops when the color is different.

I've increased the recursion limit and the stack size is 64 mB.

Here is a simplified version of it:

from pygame import *
from sys import *
from math import *
from threading import *

screen = display.set_mode((800,600)) #Same size as my real paint canvas
white = (255,255,255)
red = (255,0,0)
brush = Rect(0,0,25,25)
bucket = Rect(30,0,25,25)
running = True
tool = 1

setrecursionlimit(20000)
stack_size(67108864)
screen.fill(white)
draw.rect(screen,0,(0,0,25,25),0)
draw.rect(screen,0,(30,0,25,25),0)

def fill(x,y,oldColor,newColor,n1,n2,n3,n4):
    if n1 >=800 : #Stops flooding right when it exceeds width
        return
    if n2 <= 0: #Stops flooding left
        return
    if n3 >= 600: #Stops down
        return
    if n4 <= 0: #Stops up
        return
    try:
        if screen.get_at((x,y)) != oldColor:
        return
    except IndexError:
        return
    draw.rect(screen,newColor,(x,y,1,1),0)
    fill(x+1,y,oldColor,newColor,n1=n1+1,n2=n2,n3=n3,n4=n4) #Floods right
    fill(x-1,y,oldColor,newColor,n1=n1,n2=n2-1,n3=n3,n4=n4) #Left
    fill(x,y+1,oldColor,newColor,n1=n1,n2=n2,n3=n3+1,n4=n4) #Down
    fill(x,y-1,oldColor,newColor,n1=n1,n2=n2,n3=n3,n4=n4+1) #Up

while running:
    for e in event.get():
        if e.type == QUIT:
            running = False
    mb = mouse.get_pressed()
    mx,my = mouse.get_pos()
    if brush.collidepoint(mx,my) and mb[0] == 1:
        tool = brush
    if bucket.collidepoint(mx,my) and mb[0] == 1:
        tool = fill
    if tool == brush and mb[0] == 1:
        draw.circle(screen,red,(mx,my),5,0)
    if tool == fill and mb[0] == 1:
        pixel = screen.get_at((mx,my))
        fill(mx,my,pixel,red,mx,mx,my,my)
    display.flip()
quit()

Anyone know why Pygame freezes after I fill a shape?

Answer 1

Your typo with regard to n4 (n4 = n4 + 1) doesn't properly bounds check going off the top of the screen. Your rectangle that you're drawing and presumably clicking on to test this touches the top of the screen. It recurses upwards forever.

I also made some other comments above on how to clean this up significantly.

Answer 2

instead of this:

for e in event.get():
        if e.type == QUIT:
            running = False

try this:

if e.type == pygame.KEYDOWN:
       if e.key == pygame.K_ESCAPE:
           running = False

that helps me stop lag and the wheel of death.