CHALLENGE 2: Moving Downward and Printing Once
====================================================================

TASK
----
Write a script attached to a Sprite2D that continuously moves it
downward at 80 pixels per second using _physics_process. Once its
position.y passes 400, print "Reached the bottom" exactly once (not
on every frame after).

SOLUTION CODE (attached to the Sprite2D)
--------------------------------------------
extends Sprite2D

const SPEED = 80.0

var has_reached_bottom: bool = false

func _physics_process(delta: float) -> void:
    position.y += SPEED * delta

    if position.y > 400 and not has_reached_bottom:
        print("Reached the bottom")
        has_reached_bottom = true

WHY THIS WORKS AS AN ANSWER
----------------------------
position.y += SPEED * delta is the same frame-rate-independent
movement pattern from the chapter, applied to the Y axis instead of
X - since Y increases downward in Godot, continuously adding to it
moves the sprite down the screen over time, exactly as the task
describes.

The tricky part of this challenge is the "exactly once" requirement.
_physics_process runs many times per second, so a plain
"if position.y > 400: print(...)" would print on every single frame
after the sprite passes y=400, not just the first one. The
has_reached_bottom boolean flag solves this: it starts false, and
the print only happens when position.y > 400 AND has_reached_bottom
is still false. The moment it prints, has_reached_bottom is flipped
to true, so every subsequent frame's check fails on the second
condition even though position.y > 400 remains true forever after -
guaranteeing the message appears exactly once.