def check_intersection(x1, y1, x2, y2, x3, y3, x4, y4):
    # Compute denominator
    denominator = (x1 - x2) * (y3 - y4) - (y1 - y2) * (x3 - x4)

    # If denominator is zero, lines are parallel or coincident
    if denominator == 0:
        return False

    # Compute t and u
    t = ((x1 - x3) * (y3 - y4) - (y1 - y3) * (x3 - x4)) / denominator
    u = ((x1 - x2) * (y1 - y3) - (y1 - y2) * (x1 - x3)) / denominator

    # Check if intersection occurs within segment bounds
    return 0 <= t <= 1 and 0 <= u <= 1

# Player movement segment
x1, y1 = player.old_x, player.old_y
x2, y2 = player.new_x, player.new_y

crossed_border = False

# Check against all border segments
for border in border_list:
    x3, y3 = border.x1, border.y1
    x4, y4 = border.x2, border.y2

    if check_intersection(x1, y1, x2, y2, x3, y3, x4, y4):
        crossed_border = True
        break  # Stop checking after first intersection

# If crossed, revert movement
if crossed_border:
    player.new_x = player.old_x
    player.new_y = player.old_y