in scripts/Player.cs [19:27]
public override void _PhysicsProcess(double delta)
{
// Move up and down based on input.
var input = Input.GetActionStrength("ui_down") - Input.GetActionStrength("ui_up");
var position = Position; // Required so that we can modify position.y.
position += new Vector2(0, (float)(input * moveSpeed * delta));
position.Y = Mathf.Clamp(position.Y, 16, GetViewportRect().Size.Y - 16);
Position = position;
}