[pygame] Fullscreen vs Windowed Alpha Blit speed?

[Fred Burton <flbl@xxxxxxxxxxxxxx>]

I was writing a simple slideshow program last night (which fades images 
in and out),
and was wondering why for some reason bliting with alpha seems to run 
much slower when in fullscreen than when not.

Can someone tell me how to make it run as fast in fullscreen as in a 
window? (I tried a few things last night, but none of them seemed to help)

import pygame
import os

fade_time = 1000
hang_time = 10000
imgdir = 'images/'

fullscreen = 0
bgcolor = 0

# 20 minute software by Fred Burton: flbl@xxxxxxxxxxxxxx


files = os.listdir(imgdir)

pics = []
for pic in files:
    if pic.lower()[-4:] == '.jpg':
        pics.append(pic)

pics.sort()


class ErrorQuit:
    pass

skip = '*'

def think():
    global gamequit
    global skip
    remainingEvents = pygame.event.get()
    for event in remainingEvents:
        if event.type == pygame.QUIT:
            raise ErrorQuit
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_ESCAPE:
                raise ErrorQuit
            if event.key == pygame.K_SPACE:
                skip = 1
            if event.key == pygame.K_n:
                skip = 1
            if event.key == pygame.K_p:
                skip = -1
            if event.key == pygame.K_b:
                skip = -1
        if event.type == pygame.MOUSEBUTTONDOWN:
                if event.button == 1:
                    skip = 1
                if event.button == 3:
                    skip = -1            



def find_pred(name):
    dl = pics
    if len(dl) == 0:
        return None
    try:
        i = dl.index(name)
    except:
        return dl[-1]
    i -= 1
    if i<0:
        i = -1
    return dl[i]

def find_succ(name):
    dl = pics
    if len(dl) == 0:
        return None
    try:
        i = dl.index(name)
    except:
        return dl[0]
    i += 1
    if i>=len(dl):
        i = 0
    return dl[i]


try:
    
    pygame.init()
    if fullscreen:
        screen = pygame.display.set_mode((1024,768), pygame.DOUBLEBUF | pygame.FULLSCREEN)
    else:
        screen = pygame.display.set_mode((1024,768), pygame.DOUBLEBUF)
        
    ifname = pics[0]
    while (1):
        if skip == -1:
            ifname = find_pred(ifname)
        elif skip != '*':
            ifname = find_succ(ifname)
        skip = 0
            
        img = pygame.image.load(imgdir+ifname)
#        pos = (0,0)
        pos = (0.5*(screen.get_width()-img.get_width()), 0.5*(screen.get_height()-img.get_height()))
        
        t0 = pygame.time.get_ticks()
        t1 = t0
        while (t1-t0)<fade_time:
            n = (255*(t1-t0))/fade_time
            screen.fill(bgcolor)
            img.set_alpha(int(n))
            screen.blit(img, pos)
            pygame.display.flip()
            think()

            pygame.time.wait(1)
            t1 = pygame.time.get_ticks()
        
        img.set_alpha(255)
        screen.blit(img, pos)
        pygame.display.flip()
        
        t0 = pygame.time.get_ticks()
        t1 = t0
        while ((t1-t0)<hang_time) and (skip == 0):
            n = (255*(t1-t0))/fade_time
            think()
            pygame.time.wait(10)
            t1 = pygame.time.get_ticks()
        
        t0 = pygame.time.get_ticks()
        t1 = t0
        while (t1-t0)<fade_time:
            n = 255-((255*(t1-t0))/fade_time)
            screen.fill(bgcolor)
            img.set_alpha(int(n))
            screen.blit(img, pos)
            pygame.display.flip()
            pygame.time.wait(1)
            think()
            t1 = pygame.time.get_ticks()
        
        screen.fill(bgcolor)
        pygame.display.flip()

finally:
    pygame.quit()