CHALLENGE 1: A Player That Stops at Walls
====================================================================

TASK
----
Build a CharacterBody2D with a CollisionShape2D (a real shape
assigned), plus a couple of static wall nodes with their own
collision shapes nearby. Attach the four-directional
move_and_slide() controller from this chapter and confirm the
character stops at the walls instead of passing through.

SCENE STRUCTURE
----------------
Root (Node2D)
|-- Player (CharacterBody2D)
|   |-- Sprite2D
|   |-- CollisionShape2D  (Shape: RectangleShape2D, sized to the sprite)
|-- Wall1 (StaticBody2D)
|   |-- CollisionShape2D  (Shape: RectangleShape2D)
|-- Wall2 (StaticBody2D)
    |-- CollisionShape2D  (Shape: RectangleShape2D)

(StaticBody2D is the node type used for immovable scenery like
walls and floors - it participates in collision but, unlike
RigidBody2D, never moves on its own.)

SOLUTION CODE (attached to Player)
--------------------------------------
extends CharacterBody2D

const SPEED = 200.0

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

TESTING IT
----------
Run the scene and move the Player toward Wall1 or Wall2 using the
arrow keys / WASD. The character should stop right at the wall's
edge - it can slide along the wall if approaching at an angle, but
it can never pass through it.

WHY THIS WORKS AS AN ANSWER
----------------------------
Because Player extends CharacterBody2D (not Sprite2D directly, as
in earlier chapters), setting velocity and calling move_and_slide()
does real, collision-aware movement instead of blindly changing
position. move_and_slide() checks the Player's own CollisionShape2D
against every other collision shape in the scene - including
Wall1's and Wall2's - and stops (or slides along) the movement the
moment it would overlap one of them.

This only works because every node involved has a real Shape
assigned to its own CollisionShape2D, per this chapter's own warning
- an empty CollisionShape2D on either the Player or a wall would
make that node invisible to collision entirely, and the character
would pass straight through as if the wall weren't there.