compsci_godot_albert/_subsections/sec03/lesson-30.org

#+title: Section 03 - Lesson 30 | Section Review
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* Links
- [[../../toc.org][TOC - Godot Notes]]
- [[https://www.udemy.com/course/jumpstart-to-2d-game-development-godot-4-for-beginners/learn/lecture/45070537#overview][S03:L42.30 - Section Review]]

* Notes

** paddle scene
*** node composition
- root: Area2D
- Sprite2D
- CollisionShape2D

*** script view: paddle.gd
- extends Area2D

**** use *@export* to create speed variable
  - can be modified in Inspector
  - give default value

**** override _process function
  - check if =Input.is_action_pressed=
    - is 'left'
    - is 'right'

  - move paddle
    - get the Node2D.position property
      - multiply speed by delta and add or subtract it from position.x
      - delta is number of seconds that elapsed since the previous frame

** gem scene
*** node composition
- root: Area2D
- Sprite2D
- CollisionShape2D

*** script view: gem.gd
- extends Area2D

**** set class name
- =class_name Gem=
- this allows us to instantiate Gem objects in scripts

**** set a signal property
- =signal on_gem_off_screen=
- allows us to attach listeners who will be notified when we emit a signal

**** set export property
- =@export var speed=
- lets us set the speed in the Inspector

*** modify _process
**** determine if the gem has gone out of bounds
- this is going to be the edge of the viewport
- check position property against the viewport rect property
  #+begin_src gdscript
  if position.y > get_viewport_rect().size.y
  #+end_src

**** if gem went out of bounds
***** emit signal
#+begin_src gdscript
on_gem_off_screen.emit()
#+end_src

***** stop the gem and remove it from the node tree
- stop going through the process function
- delete node at the end of the current frame
#+begin_src gdscript
set_process(false)
queue_free()
#+end_src

** Game scene
*** preload assets
- using const to set builtin preload function
 #+begin_src gdscript
  const EXPLOSDE = preload("res://assets/explode.wav")
 #+end_src

*** add a PackedScene variable
  - allows us to instantiate gem scenes
  - export allows us to drag and drop the scene we want into the inspector
      #+begin_src gdscript
      @export var gem_scene: PackedScene

	      # when time comes to use it
	      gem_scene.instantiate()
	      add_child(gem_scene)
      #+end_src

  - otherwise we would have to preload it
      #+begin_src gdscript
	      gem_scene = preload("res://somescene.tscn").instantiate()
	      add_child(gem_scene)
      #+end_src

*** use onready to add nodes in tree scene
#+begin_src gdscript
@onready var label: Label = $Label
@onready var timer: Timer = $Timer
@onready var audio_stream_player_2d: AudioStreamPlayer2D = $AudioStreamPlayer2D
#+end_src

- these are all scenes in the Game tree
- use onready to attach them to variables for use in game script
- onready makes sure it's available so we dont end up with a null reference

*** spawn gem at _ready
- in the ready function immediately call spawn_gem
- spawn Gem instantiates a gem scene and type casts it to a Gem class
- connect any signals
- set it's position
- add it as a child
  #+begin_src gdscript
  var new_gem: Gem = gem_scene.instantiate()
  new_gem.on_gem_off_screen.connect(game_over)
  new_gem.position = Vector2(xpos, ypos)
  add_child(new_gem)
  #+end_src

*** stop all function
- stop the timer
- run through all children and set process to false
  #+begin_src gdscript
  timer.stop()
  for child in get_children():
	  child.set_process(false)
  #+end_src

*** turn off audio
- get references to audio and call 'stop' function
- you can also set another sound for ending and play that

#+begin_src gdscript
 audio_stream_player_2d.stop()
 audio_stream_player_2d.stream = EXPLODE
 audio_stream_player_2d.play()
#+end_src

*** whenever timer times out spawn a gem
- we attached the timer to a signal to call a function that calls spawn gem

*** when the paddle gets hit by a gem
- increase score
- set the position of where the paddle got hit to the audio and play a sound
- free up the hit object (the gem)

#+begin_src gdscript
func _on_padd_area_entered(area: Area2D) -> void:
	_score += 1
	label.text = "%05d" % _score
	audio_stream_player_2d.position = area.position
	audio_stream_player_2d.play()
	area.queue_free()
#+end_src