[Python] How do I make objects in pygame scroll while focusing on a single object? [duplicate]

I'm creating a game in pygame, in which you have to stop the ball from falling out of the screen and keep it up for as long as possible by creating line segments from which it bounces off. I have done most of the physics and logic stuff, but I want to make the lines move down instead of the ball moving up (which creates a similar effect). The ball should stay stationary in one place and all the other objects should "scroll" downwards.

main.py

import pygame
import colorspy
from line import Line, THICKNESS
import random

pygame.init()

WIDTH, HEIGHT = 500, 800
win = pygame.display.set_mode((WIDTH, HEIGHT))
pygame.display.set_caption("Linez")

last_pos = (192, 500)
circles = [last_pos]
lines = []
current_line = None

ball = pygame.Vector2(200, 80)
radius = 10
touching = False
vel = pygame.Vector2()
G = 440

offset = pygame.Vector2(0, 0)

clock = pygame.time.Clock()
run = True
while run:
dt = clock.tick(60)/1000
touching = False

for event in pygame.event.get():
if event.type == pygame.QUIT:
run = False

if event.type == pygame.MOUSEBUTTONDOWN:
current_pos = pygame.mouse.get_pos()
if current_pos != last_pos:
circles.append(current_pos)
lines.append(Line(last_pos, current_pos))
last_pos = current_pos
current_line = lines[-1]

win.fill(colorspy.midnight_blue)

for circle in circles:
pygame.draw.circle(win, colorspy.white, circle, 8)

for line in lines:
pygame.draw.line(win, colorspy.white, line.p1, line.p2, THICKNESS)

pygame.draw.circle(win, colorspy.dark_orange, ball, radius)

touching = False
if current_line != None:
if current_line.collide(ball, radius):
normal = pygame.Vector2(-current_line.normal.y, current_line.normal.x)

dot = vel.dot(normal)
vel = vel - 2 * dot * normal

# Nudge the ball out to prevent sticking
#ball += normal * 2

touching = True

if not touching:
vel.y += G * dt
ball += vel * dt

offset.y += vel.y * dt

if ball.x - radius > WIDTH:
ball.x = -radius
elif ball.x + radius < 0:
ball.x = WIDTH + radius

pygame.display.update()

pygame.quit()


line.py

import pygame
import math


THICKNESS = 5
ACC = 0.2


class Line:
def __init__(self, start, end):
self.p1 = pygame.Vector2(start)
self.p2 = pygame.Vector2(end)
self.res = self.p2 - self.p1
self.length = self.p1.distance_to(self.p2)
self.angle = math.atan2(self.res.y, self.res.x)
self.normal = self.res.normalize()

def point_circle(self, px, py, ball, r):
return ball.distance_to(pygame.Vector2(px, py)) <= r

def line_point(self, ball):
dist1 = ball.distance_to(self.p1)
dist2 = ball.distance_to(self.p2)

return (dist1 + dist2) > self.length - ACC and (dist1 + dist2) < self.length + ACC

def collide(self, ball, radius):
inside1 = self.point_circle(self.p1.x, self.p1.y, ball, radius)
inside2 = self.point_circle(self.p2.x, self.p2.y, ball, radius)

if inside1 or inside2:
return True

dot = ( ((ball.x-self.p1.x)*(self.p2.x-self.p1.x)) + ((ball.y-self.p1.y)*(self.p2.y-self.p1.y)) ) / (self.length * self.length)

x = self.p1.x + (dot * (self.p2.x - self.p1.x))
y = self.p1.y + (dot * (self.p2.y - self.p1.y))

on_segment = self.line_point(pygame.Vector2(x, y))
if not on_segment:
return False

dist = ball.distance_to(pygame.Vector2(x, y))

return dist <= radius


I tried creating an offset vector with the velocity of the ball and adding it to all the objects, but it didn't seem to work properly. Is there a way I could implement this without redoing my entire code?

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