About Scheme REPL with Cocos2Dx
This is a demo for developers. Please don't give low ratings based on playability - it's not meant to be a complete game! It may still be entertaining though, you can drive a truck up hills and fall back down.
=== What this is about ===
We have wanted to try REPL-based game development for a long time, and this is our attempt.
A REPL is like a command-line interface to the inside of your running program. It's like having a debugger running constantly, but perhaps less troublesome.
REPL-based development should allow us to develop games and apps much faster. Your new code takes effect immediately, and can be executed on your target hardware.
Bret Victor has a very nice talk about immediate feedback in his "Inventing on Principle" talk: http://vimeo.com/36579366
This project is an attempt to accomplish this, and so far it seems to have worked fairly well!
=== How we are doing this ===
The demo combines three third-party libraries:
- Chicken Scheme for the REPL
- Cocos2Dx for graphics
- Chipmunk for physics
Cocos2Dx is a C++ library with 2D-games in mind. It lets you manage things like sprites, their animations and touch events. It is fast and portable (Android, iOS and others). Chipmunk is a physics engine writtten in C. It's fast with a very nice API. Chicken Scheme is a Scheme-to-C compiler and interpreter.
All should also run on iOS, but I don't have a Mac.
=== Bindings ===
The Cocos2Dx bindings are in an early-stage. Basic functions to manipulate sprites are available:
- (CCSprite::create "CloseNormal.png")
- (setPosition *sprite* x y)
- (getLocatino touch-event)
The Chipmunk API is more mature. You can read about the `chickmunk` project on https://github.com/kristianlm/chickmunk.
=== Try it yourself ===
You can connect to the REPL directly from your laptop if your phone is on the same WiFi, or use USB. Try Settings->Wireless Networks->Wifi Settings-> [Menu]->Advanced when looking for you phone's IP.
With netcat (or Emacs, with netcat [ip] [port] as your Scheme interpreter), you could try:
$ nc [phone ip] [port]
Alternatively, you could use USB with adb and forward:
$ adb forward tcp:1234 tcp:1234
$ nc localhost 1234
Once you see the REPL prompt @>, you can play around:
;; 'import' chipmunk bindings
(use chickmunk)
;; where is the player?
(body-get-pos truck)
;; redefine game-loop to pause game unless you're touching the screen
(define (*update*)
(if *touch-down* (space-step space (/ 1 120))))
;; now let's give the truck a gentle push
(body-set-ang-vel wf -20)
;; now touch the screen to watch it drift off
;; restart the app to revert your changes
(exit)
;; You can also manipulate the physics-world:
;; Drop a ball from the sky
(space-add space
`(body ((pos (320 700)))
(circle (density 0.001)
(friction 1)
(radius 10))))
;; Add a gentle but slippery slope
(space-add space
`(body ((static 1))
(segment (friction 0.1)
(endpoints ((250 500)
(800 550))))))
;; type this to see the touch-down state:
*touch-down*
;; it should be #f when your finger is off the screen, and touch-coordinates otherwise. evaluate it while holding the screen to try it out!
This is just a small example of what can be done. As a matter of fact, almost everything in the demo itself was developed this way: the REPL, Emacs and Inferior Scheme.
=== Source code ===
The source-code for the demo can be found on github: https://github.com/Adellica/cocoscheme.
Please give feedback, let us know if you like this! And please let us know of any similar efforts. Thanks!
Download and install
Scheme REPL with Cocos2Dx version 1.0 on your
Android device!
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Android package:
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by C####:
This game changed me