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#+title: Lesson 12: Player-Enemy Collisions


* Links
- [[../../arpg/toc.org][< Back to Main TOC]]
- [[https://youtu.be/WVQkOWY3zxQ?si=UILX6fBQ_Zw1cZoK][Player-enemy collision]]



* Notes
** add collision shape to enemy sprite
- add CollisionShape2D to sprite root

*** add shape
- select collision shape 2D node from Scene Panel
- Go to Inspector->CollisionShape2D->Shape
- select 'CapsuleShape2D' from dropdown

*** modify shape
- Inspector->CollisionShape2D->Node2D->Transform
- Go to Rotation and set to 90 degrees
- Modify shape via handles to adjust it over sprite

*** set the z-index
- in CollisionShape2D to 0
- in sprite root node to 1

*** make sure collision shape fits all the animation frames
- go to the AnimateSprit2D node
- Inspector->AnimatedSprite2D->Animation->Frame
- scroll through the frames to see if they fit the collision shape properly

** */method 1/*: using character bodies and collision shapes

*** default collision code
- default collision handling occurs between two CharacterBody2D nodes
- limits each others movements
- occurs after the =move_and_slide= function is called

*NOTE: you are not expected to put this into the script!!!*

#+begin_src godot
# Using move_and_collide.
var collision = move_and_collide(velocity * delta)
if collision:
    print("I collided with ", collision.get_collider().name)
#+end_src

*** handle collisions (scaffolding)
- first get the number of collisions that occurred
  - this is in =get_slide_collision_count()= function
- loop through the number with an index
  - in each loop get the /collision info object/ for that index with =get_slide_collisions()=
    - =get_slide_collision= takes an index
  - to get the /collider/ call =get_collider()= on the /collision info object/

- the function scaffolding:
#+begin_src godot
# this is the basic function
func handleCollision():
    for i in get_slide_collision_count():
        var collision = get_slide_collision(i)
        var collider = collision.get_collider()
        priint_debug(collider.name)
#+end_src

- place this function in =func _physics_process(delta)=
  - put it after =move_and_slide= but before =updateAnimation=
  - example:
#+begin_src godot
func _physics_process(delta):
    handleInput()
    move_and_slide()
    handleCollision()
    updateAnimation()
#+end_src

*** problems
- the player sprite might only have the shape on the lower part of his body and not the upper
  - this is to allow him to move the body against a tree or other object and only block by the feet
- this causes the enemy sprite to walk directly through the player

** layer and mask

*** change collision layer and mask for players
- [Player Root Node]->Inspector->CharacterBody2D->Layers
- How Layers work
  - the numbers of the layers selected determines what he looks for
  - you can change the name of the layer by clicking on the three dots to the right
- change the layers names
  - Layer 1: 'player'
  - Layer 2: 'enemy'

*** change the collision layer and mask for enemies
- [Enemy Sprite] -> [Enemy Root Node] -> Inspector -> CollisionObject2D -> Collision -> Layers
- move the sprites layer and mask to '2'

*** enabling enemy sprites to collide with tilemap
- make all enemy sprites children of the tilemap
- [Tilemap Node] -> Inspector -> TileMapLayer -> TILESET
  - INSIDE the "tileset" dropdown, click on whatever element was selected
  - this will open up the physics layer
  - set the layers and masks to /*BOTH*/ "1" and "2"

** method2: hurt box and hit box
*** basic
- add hurt box to player
- add hit box to enemy

*** create hurt box
- add Area2D node to [Player Scene]
  - you can rename it 'hurtBox'
- add a CollisionShape2D to the Area2D node
  - [hurtBox node] -> CollisionsShape2D -> Inspector -> CollisionShape2D -> Shape
    - select what shape you want from the dropdown box
- set the collision properties for the hurt box
  - [hurtBox node] -> CollisionObject2D -> Collision
  - set /*ONLY*/ the mask to "1" and "2"

*** create hit box
- go to NPC sprite
- add Area2D node
  - rename 'hitBox'
  - add CollisionShape2D to Area2D node
    - rotate it 90

* in the case where animation frames change shape

** modify sprite scene
- add AnimationPlayer node to scene
- remove AnimatedSprite2D
- add regular Sprite2D node
  - set texture on sprite
    - drag sprite texture to Sprite2D->Inspector->Sprite2D->Texture
  - set Hframes and Vframes correctly
    - Sprite2D->Inspector->Sprite2D->Animation

  - move sprite up over center of scene

** MOVE THE AREA2D FOR PROPER DRAWING
- area2D node must be lower than the Sprite2D node
- this will draw it on top of the sprite
- make it easier to animate properly

** modify AnimationPlayer node
- select node
- in lower pane, find "Animation" dropdown
  - select "New"
  - call it "walkDown"
#+attr_html: :width 400px
[[../../_share/media/img/ch12/g12_animation.png]]

- set snap to 0.2
  #+attr_html: :width 400px
  [[../../_share/media/img/ch12/animation_snap.png]]

** add sprite animations
- [Sprite2D node] -> Inspector -> Sprite2D -> Animation
- select the X and Y of Frame Coords
- click the key button
  #+attr_html: :width 250px
  [[../../_share/media/img/ch12/frame_coords.png]]

- screen should look like
  #+attr_html: :width 600px
  [[../../_share/media/img/ch12/animation_timeline.png]]

- set animation length to 0.8
- enable looping
  #+attr_html: :width 600px
  [[../../_share/media/img/ch12/length_looping.png]]

** add collision detection to the frames
- select Area2D->CollisionShape2D node
- Inspector-> Node2D-> Transform
- make sure the bottom animation panel is visible
  - select the first frame
- lock properties to the frames using key buttons
  - position
  - scale

    #+attr_html: :width 250px
    [[../../_share/media/img/ch12/lock_properties.png]]

    #+attr_html: :width 600px
    [[../../_share/media/img/ch12/lock_animation.png]]

*** go to the next FRAME in the animation panel
- adjust the shape of the collision area
- lock the properties as before

*** changing shape
- changing shape is IMPOSSIBLE
  - we must change scale
- click the chains to allow you to change x and y axis independently
- click on the text box for each to change it

*** discreate changes
- the shape will appear to not change properly with the sprite
- this is because it's update mode is set to 'continuous'
- change it to discrete on both scaling and positioning
  #+attr_html: :width 300px
  [[../../_share/media/img/ch12/discrete.png]]

*** update the rest of the animations
- duplicate the current animation
- modify and set whatever properties are necessary for each animation

** modify script
- set the animations variable from $AnimatedSprite2D to $AnimationPlayer

* Video Contents

[[https://www.youtube.com/watch?v=WVQkOWY3zxQ][Lesson Link]]

#+attr_html: :class content
- [[https://www.youtube.com/watch?v=WVQkOWY3zxQ][00:00 Introduction]]
- [[https://youtu.be/WVQkOWY3zxQ?si=vhyjv3xTfYhvAMmE&t=28][00:28 body-body collision]]
- [[https://youtu.be/WVQkOWY3zxQ?si=qLZquUVuAC-yYN1t&t=238][03:57 layer and mask]]
- [[https://youtu.be/WVQkOWY3zxQ?si=GqVUob9wQvm1YH_9&t=298][04:58 hurt boxy and hit box]]
- [[https://youtu.be/WVQkOWY3zxQ?si=rhqR5crCcWh7vgSH&t=394][06:34 hit box animation]]
- [[https://youtu.be/WVQkOWY3zxQ?si=DIBeG4TRZdhcds0g&t=711][11:51 fixing move animation]]
- [[https://youtu.be/WVQkOWY3zxQ?si=CTRznDX_bRokCO0d&t=751][12:31 hurt-hit box collisions]]
- [[https://youtu.be/WVQkOWY3zxQ?si=fUUy5KhrAFLzbWdA&t=827][13:47 outro]]