(The little gamer) Christian C-Keen Kellermann. FrOSCon s quasiconf the little gamer) FrOSCon /37

Transcription

1 the little gamer) FrOSCon /37 (The little gamer) Christian C-Keen Kellermann FrOSCon s quasiconf 2012

2 the little gamer) FrOSCon /37 Why program games? Definition of game: game noun: an amusement or pastime: children s games. webster s dictionary Games are known to ease learning So why not learn a language and have fun at the same time?

3 First steps ASCII Most programming introductions will tell you how to write text-based games They can get pretty fancy Unless you are a roguelike fan (like I am) or fond of text adventures, this will not hold attention span older machines, like the C64 did better I want pictures So why don t you get graphics in these books? Graphical IO (i.e. modern HW access) is complicated! (the little gamer) FrOSCon /37

4 SDL / GL / Allegro / WTF / BBQ Game engines and frameworks come by the dozen Different entry levels Many programming languages available Too much detail Advanced language features (the little gamer) FrOSCon /37

5 Available frameworks (a small selection) SDL Allegro Processing LÖVE How to design worlds (TeachScheme now!) (Your favourite one is probably missing... ) (the little gamer) FrOSCon /37

6 (the little gamer) FrOSCon /37 SDL This has been used by many many (more or less) popular games Fast, reliable, etc. Very low level Game loop needs to be implemented

7 (the little gamer) FrOSCon /37 Allegro Looks bigger than SDL Featurer complete, huge Supports Joysticks, Gamepads, Storage, Audio Game loop needs to be implemented

8 (the little gamer) FrOSCon /37 Processing Not really for games but visualisations Pseudo C like language + IDE Distribution is easy: Javascript, Java applet Lots of things have to be written from scratch

9 LÖVE Written in LUA Moderately big community Lots of new games Easy to get started Easy to distribute games (the little gamer) FrOSCon /37

10 How to design worlds Not really a game framework but a way of teaching programming Uses Racket as base Very nice emphasis on graphics Get the book for free (CC-BY-NC-SA 3.0) at Usage outside of classes unknown to me The exercises are fun to reprogram if you are bored. ( Why did the chicken cross the road... ) (the little gamer) FrOSCon /37

11 (the little gamer) FrOSCon /37 My favourite: CHICKEN Scheme A practical and portable Scheme system: Mailing lists: chicken-users, chicken-hackers Friendly helpers online: #chicken on freenode Comes with hundreds (> 500) extensions ( eggs ) Easy FFI to C/C++

12 (the little gamer) FrOSCon /37 Your options with CHICKEN Scheme Graphics SDL, OpenGL, GLUT Cairo Graphics Allegro simple-graphics doodle Sound OpenAL libsdlmixer Physics engines Box2D Chipmunk

13 (the little gamer) FrOSCon /37 Doodle My attempt to just open a window for graphics Goal: Find a convenient API / language / method for writing games 2D only Geared at the curious beginner and casual game programmer (like I am) Usable for games and visualisations, graphs, L-Systems, Turtlegraphics... A work in progress, still looking for the golden path...

14 (the little gamer) FrOSCon /37 Example L-Systems (define-l-system grass "F" ( "F" -> "F[+F]F[-F]F")) (draw-system grass 6 x: center-y y: h angle: -90 angle-step: 25.7 step-width: 2) (save-screenshot "grass.png")

15 Example Mouse events (the little gamer) FrOSCon /37

16 Example Tile set (the little gamer) FrOSCon /37

17 (the little gamer) FrOSCon /37 Sprites Not there yet, I am not sure of the API, demo:

18 Basic structure (use doodle) (new-doodle) ;; opens a window (define red ( )) ;; some nice transparent red (filled-circle (/ doodle-width 2) (/ doodle-height 2)) (show!) ;; If you want to save stuff (save-screenshot "circle.png") The easy way for visualisations: open a window draw things show window For games with interaction we have a game loop... (the little gamer) FrOSCon /37

19 (the little gamer) FrOSCon /37 Open the window (new-doodle #!key (width 680) (height 460) (title "Doodle") (background solid-black) (fullscreen #f)) Adjust to your own needs If background is a string, the file by that name will get loaded

20 The world Game loop (new-doodle) (world-inits (lambda ()...)) (world-changes (lambda (events dt exit-continuation)...) (world-ends (lambda ()...) (run-event-loop) Modelled after LÖVE and Processing, thanks! The world has three stages world-inits, world-changes, world-exits You can implement the ones you need Start the game loop with run-event-loop Those are (scheme) parameters, so you can reset them dynamically in the interpreter (the little gamer) FrOSCon /37

21 Drawing primitives Lines Circles Rectangles Text (True Type Fonts) Image blitting (the little gamer) FrOSCon /37

22 the little gamer) FrOSCon /37 An interactive example (use matchable doodle) (define *paint* #f) (define red ( )) (world-changes (lambda (events dt exit) (for-each (lambda (e) (match e (( mouse pressed x y 1) (set! *paint* #t) (filled-circle x y 10 red)) (( mouse released x y 1) (set! *paint* #f)) (( mouse moved x y) (when *paint* (filled-circle x y 10 red))) (( key pressed #\esc) (exit #t)) (else (void)))) events))) (new-doodle title: "Doodle paint" background: solid-white) (run-event-loop)

23 (the little gamer) FrOSCon /37 Beesteroids Heavily influenced by Andy Diver s CL version: Ships, Rockets, Space! Gets unnecessary cruel later in the game Was done in 333 lines of code (sloccount) A tiny portion of the code has to do with actual graphics or sound!

24 Beesteroids Screenshot (the little gamer) FrOSCon /37

25 (Poor) Design Choices No object system is used but regular scheme records All drawable objects are things All things have a velocity and a direction Vectors and points are just lists Things are drawn as polygons, which points are stored and transformed Objects should wrap around the screen when they leave, but only whole objects are drawn (the little gamer) FrOSCon /37

26 the little gamer) FrOSCon /37 The things: Like... a ship (define (make-ship #!key (angle (random 360)) heading (pos center) (radius 30) velocity (speed 0) (thrust 0)) (let* ((h (or heading angle)) (nose (radial-point-from pos radius h)) (left (radial-point-from pos radius (- h 130))) (right (radial-point-from pos radius (+ h 130))) (tail (radial-point-from pos (round (* radius 0.5)) (+ h 180))) (velocity (or velocity (map - (radial-point-from pos speed angle) pos)))) (make-thing ship pos velocity h thrust radius (list nose left tail right))))

27 (the little gamer) FrOSCon /37 Drawing things... ;; Draws a polygon from a list of points (define (draw-poly points) (unless (null? points) (let loop ((ps (cdr points)) (last (car points))) (cond ((null? ps) (line last (car points))) (else (line last (car ps)) (loop (cdr ps) (car ps))))))) ;; This draws the polygon of a thing (define (draw-thing thing) (draw-poly (thing-edges thing)) (when *debugging* (let ((pos (thing-pos thing))) (circle (first pos) (second pos) (* 2 (thing-bounding-radius thing)) ( )) (line pos (map + (map (cut * 100 <>) (thing-velocity thing)) pos))))) ;; Draw all things (define (draw-things. list-of-things) (for-each (lambda (things) (for-each draw-thing things)) list-of-things))

28 (the little gamer) FrOSCon /37 Dodging Bullets: Movement ;; Move one thing around (define (move-thing dt t) (let* ((pos (thing-pos t)) (thrust (* dt (thing-thrust t))) (heading (thing-heading t)) (velocity (thing-velocity t)) (thrust-vec (map - (radial-point-from pos thrust heading) pos)) (scaled-vel (map (cut * 100 <> dt) (map + velocity thrust-vec))) (new-vel (map + velocity thrust-vec))) (thing-pos-set! t (map + pos scaled-vel)) (thing-edges-set! t (map (lambda (e) (map + e scaled-vel)) (thing-edges t))) (thing-velocity-set! t new-vel))) ;; Move objects around (define (move-things time-delta. list-of-things) (for-each (lambda (things) (for-each (lambda (t) (move-thing time-delta t)) things)) list-of-things))

29 (the little gamer) FrOSCon /37 All the things belong somewhere... The world object holds asteroids, bullets, our ship and everything the game rules need. (define-record world paused? level lives score bullets-left shield bullets asteroids ship)

30 (the little gamer) FrOSCon /37 Hits and misses: Collision detection Works on the world, as it influences world state such as lives, score etc. (define (check-collisions world) (let ((bullets (world-bullets world)) (ship (world-ship world)) (asteroids (world-asteroids world))) (cond ((find (cut collides? ship <>) asteroids) => (lambda (a) (if (zero? (world-shield world)) (ship-wrecked) (begin (world-asteroids-set! world (delete a asteroids)) (asteroid-destroyed a)))))) (for-each (lambda (b) (cond ((find (cut collides? b <>) asteroids) => (lambda (a) (world-asteroids-set! world (delete a asteroids)) (world-bullets-set! world (delete b bullets)) (world-bullets-left-set! *w* (add1 (world-bullets-left *w*))) (asteroid-destroyed a))))) bullets)))

31 (the little gamer) FrOSCon /37 Putting it together DEMO!

32 Need it simpler? The simple-graphics extension by Alaric Snell-Pym gives you turtle graphics In a REPL! Easy to save pictures Approved by real children (the little gamer) FrOSCon /37

33 Adding sound OpenAL bindins and SDL mixer bindings available Beesteroids uses sdl-mixer The sdl-mixer extension is an attempt to make the API more scheme like There is one piece of music and there are samples, you can play them all at the same time (open-audio) (set! *thrust-sound* (load-sample "assets/thrusters.wav")) (set! *firing-sound* (load-sample "assets/firing-rocket.wav")) (set! *explosion-sound* (load-sample "assets/explosion.wav")) (set! *background-music* (load-music "assets/myveryowndeadship.ogg")) (play-music *background-music*) (music-finished (lambda () (play-music *background-music*))) ; meanwhile somewhere else... (when (< 0 bullets-left) (play-sample *firing-sound* channel: 2 duration: 1000)) ; much later... (close-audio) the little gamer) FrOSCon /37

34 Lessons learned so far during game sprints I always come back to a OO like model of the world no matter how hard I resist UI handling is not hard but cumbersome I am not there yet (the little gamer) FrOSCon /37

35 (the little gamer) FrOSCon /37 Things I would like to work on in the future Better collision detection support in doodle Direct access to the graphics engine w/o cairo (Optional) integration of sound

36 (the little gamer) FrOSCon /37 What to take home Game programming is easy if your language helps you Programming games in a lisp is fun There are options for evey skill level in CHICKEN Scheme

37 (the little gamer) FrOSCon /37 Where to go from here? Find these slides on the froscon pages or at: More doodle examples on my blog: Grab beesteroids and enhance it, play it, make it your own: $ git clone git@bitbucket.org:ckeen/beesteroids.git Flamewars criticisms, thoughts, questions can be directed to me also via C-Keen on IRC (drop by in #chicken on on twitter ckeen@pestilenz.org