CHALLENGE 3: A Full Player Controller That Faces Its Direction
====================================================================

TASK
----
Build the full four-directional player controller from this
chapter. Extend it so that whenever direction.x is negative, the
sprite's flip_h (from Chapter 4) is set to true, and false whenever
it's positive - so the character visually faces the direction it's
moving.

SETUP
-----
Input Map actions: move_left, move_right, move_up, move_down, each
bound to the arrow keys (or WASD).

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

const SPEED = 200.0

func _physics_process(delta: float) -> void:
    var direction := Input.get_vector("move_left", "move_right", "move_up", "move_down")
    position += direction * SPEED * delta

    if direction.x < 0:
        flip_h = true
    elif direction.x > 0:
        flip_h = false

WHY THIS WORKS AS AN ANSWER
----------------------------
The movement half is unchanged from the chapter's own player
controller: Input.get_vector() returns a normalized direction from
the four named actions, and position += direction * SPEED * delta
applies it every physics frame.

The facing logic is a straightforward if/elif check on direction.x,
the horizontal component of that same Vector2 - if it's negative,
the player is moving left, so flip_h is set true to mirror the
sprite; if it's positive, moving right, so flip_h is set false to
show it unflipped. Deliberately using if/elif rather than if/else
here matters: when direction.x is exactly 0 (moving purely up, down,
or not moving at all), neither branch runs, which correctly leaves
flip_h exactly as it already was - the character keeps facing
whichever way it was last facing horizontally, rather than snapping
back to a default orientation every time it moves purely vertically.