Arcadia's Hello World

Douglas P. Fields, Jr.
symbolics at lisp.engineer

1. Create a new, blank Unity 2D game, using Unity 5.4.0f3.

2. Unity menu: Edit -> Project Settings -> Player

   • Resolution & Presentation -> Run in Background* -> CHECK
   • Other Settings -> Api Compatibility Level -> .NET 2.0

3. Clone Arcadia Github into Assets directory and let Unity load it (be patient)

4. cd Assets/Arcadia/Infrastructure and run the ./repl program there, then

   • (require '[arcadia.core :refer :all])
   • Leave the REPL open for later

5. Drag a (random, small) image into your Unity Assets pane/window

6. Drag that image from the Assets window into the Scene pane/window, on top of the camera icon.

   • Confirm that the Hierarchy pane shows your image (it will be a Sprite now)

7. Rename that in the Hierarchy window to object-1

8. Create a new Clojure file in pathname Assets/minimal/core.clj with the contents below.

9. In the REPL, run this: (require '[minimal.core :refer :all]) to load it into the REPL

10. Now the magic happens: We're going to have the function first-callback get called every frame by linking (hooking) it to the object-1 object in the scene. This can only be done in the REPL for now, but the hook will show up in the Scene in the inspector. This will, for now, just spam the Unity Console window with boring messages.

11. We can access game objects by name using the Arcadia function objects-named. This returns a list. REPL: user=> (objects-named "object-1") -> (#unity/GameObject -22008)

12. Add the hook for the function in our minimal/core.clj file to the sprite we named object-1 in the REPL: user=> (hook+ (first (objects-named "object-1")) :update #'minimal.core/first-callback) -> #unity/GameObject -22008

13. Confirm this by clicking on object-1 in the Unity Hierarchy window and note in the Inspector that it says Update Hook (Script) with #'minimal.core/first-callback.

14. Make sure the Console window is showing. Click Play icon in Unity. Be patient. After a short time, your first Arcadia app will start running and the Console window will start showing a lot of messages like: Hello, Arcadia from UnityEngine.Debug:Log(Object).

15. Save your scene (whatever name you want). Quit Unity. Restart Unity and load your project. Hit Play. Everything should still work.

Assets/minimal/core.clj v1

(ns minimal.core
  (:use arcadia.core arcadia.linear))

(defn first-callback [o]
  (arcadia.core/log "Hello, Arcadia"))

Getting Input

1. We need to enhance the namespace to use some Unity objects. Modify the ns in the top as per the minimal/core.clj v2 code below.

2. Write a function which reads keys and prints something.

   • Input/GetKey returns true every update when a key is held down.
   • Input/GetKeyDown returns true only the first update a key has been pressed
   • See code below for move-when-arrow-pressed

3. Remove our old Hello World hook to first-callback in the Unity GUI by clicking the gear icon next to Update Hook (Script) when object-1 is showing in the Inspector window. Choose Remove Component.

4. Tell Arcadia that our .clj file has changed by using this command in the REPL: (require 'minimal.core :reload). The Arcadia team will probably have a file watcher in the future that may obviate this step.

5. In the REPL, add our new hook: (hook+ (first (objects-named "object-1")) :update #'minimal.core/move-when-arrow-pressed)

   • Confirm this by checking the Inspector for object-1 in Unity

6. Run the game, and tap & hold various arrow keys.

Assets/minimal/core.clj v2

(ns minimal.core
  (:import [UnityEngine Input KeyCode Camera Physics Time Camera])
  (:use arcadia.core arcadia.linear))

;; Log a message when arrow keys are first pushed
(defn move-when-arrow-pressed [o]
  (when (Input/GetKeyDown KeyCode/UpArrow)
    (arcadia.core/log "Up pushed"))
  (when (Input/GetKeyDown KeyCode/DownArrow)
    (arcadia.core/log "Down pushed"))
  (when (Input/GetKeyDown KeyCode/RightArrow)
    (arcadia.core/log "Right pushed"))
  (when (Input/GetKeyDown KeyCode/LeftArrow)
    (arcadia.core/log "Left pushed")))

;; Hook our new move callback
#_
(hook+ (first (objects-named "object-1")) :update #'minimal.core/move-when-arrow-pressed)

Using Input

TODO: Use the input to modify the location of the object.

Programmatically Controlling Game Objects

TODO: Generate and remove game objects, and change the sprite they display, etc.