PyGame: графики рисуются "перевернутыми"

import pygame
import math
 
def scale(x, A0, B0, A1, B1):
    return float(x-A0)/(B0-A0)*(B1-A1)+A1
 
SIZE = 760, 540
 
pygame.init()
screen = pygame.display.set_mode(SIZE)
 
print('Enter function:')
txtfunc = input()
 
print('Enter ODZ a,b:')
odz = input().split(',')
 
a = int(odz[0])
b = int(odz[1])
fmin = 100000000
fmax = -100000000
N = 50
step = (b - a) / N
pointlist = list()
x = a
while x <= b:
    if eval(txtfunc) < fmin:
        fmin = eval(txtfunc)
    if eval(txtfunc) > fmax:
        fmax = eval(txtfunc)
    x = x + step
x = a
while x <= b:
    bx = scale(x, a, b, 0, 760)
    by = scale(eval(txtfunc), fmin, fmax, 0, 540)
    pointlist.append([bx,by])
    x = x + step
print(pointlist)
pygame.draw.lines(screen, pygame.Color("tomato"), False, pointlist)
 
 
 
pygame.display.flip()
 
while True:
    ev = pygame.event.wait()
    if ev.type is pygame.QUIT:
        break

bx = scale(760-x, a, b, 0, 760)

pointlist.append([760-bx, by])

pointlist.append([bx, 540-by])

import pygame
from math import *
# l"x:sin(x)"
 
def get_input():
    #return eval("lambda x: "+input())
    return eval("lambda "+input())
 
def scale(x,sec1,sec2):
    return sec2[0]+(sec2[1]-sec2[0])*(x-sec1[0])/(sec1[1]-sec1[0])
 
pygame.init()
display=pygame.display.set_mode((640,480))
fun = sin # надо вводить
 
A,B=-7,7 #надо вводить
YA,YB=-1,1 #fun(argument)
approx=150 #надо вводить
X = [A+(B-A)*i/(approx-1) for i in range(approx)]
D = [(x,fun(x)) for x in X]
graph = [(scale(x,(A,B),(0,640)),scale(y,(YA,YB),(290,0))) for x,y in D]
pygame.draw.aalines(display,(255,50,50,255),False,graph)
 
while pygame.event.wait().type !=pygame.QUIT:
         pygame.display.flip()

import pygame
 
pygame.init()
 
screen_width, screen_heigth = 760, 540
screen = pygame.display.set_mode((screen_width, screen_heigth)) #окно игры
 
blue = 0, 0, 255
point1 = 10, 530
point2 = 750, 530
 
point3 = 10, 530
point4 = 10, 10
 
runtime = True
 
while runtime:
        for e in pygame.event.get():
            if e.type == pygame.QUIT or e.type == pygame.KEYDOWN and e.key == pygame.K_ESCAPE:
                    runtime = False
          
        screen.fill((0,0,0))
 
        pygame.draw.line(screen, blue, point1, point2)
        pygame.draw.line(screen, blue, point3, point4)
 
        for i in range(20,750, 10):
            pygame.draw.line(screen, blue, (i, 525), (i,535))
 
        for i in range(520,10, -10):
            pygame.draw.line(screen, blue, (5, i), (15,i))
 
        pygame.display.flip()
 
pygame.quit()