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@@ -1,29 +1,28 @@ -* Sly +* Sly - The Living, Breathing Game Engine - Sly is a free software game engine written in GNU Guile Scheme. It + Sly is a free software game engine written in [[https://gnu.org/software/guile][Guile Scheme]]. It provides an abstraction layer above SDL and OpenGL for common game programming requirements such as: - - Meshes + - Animation - Shaders - Sprites - - Animation - Tilesets - Scene graph - - Keyboard/mouse input + - Keyboard/mouse/joystick input - Scripting - Sly differentiates itself from other game engines by providing an - interactive development environment via Guile's read-eval-print-loop - (REPL), exposing a functional API instead of an object-oriented one, - and encouraging reactive programming. + Sly differentiates itself from most other game engines by + encouraging [[http://toplap.org/about/][live coding]] and emphasizing [[http://elm-lang.org/learn/What-is-FRP.elm][functional reactive + programming]]. ** Inspiration Every programming language should have a fun, easy to use game - library. Sly draws its inspiration from great libraries/engines - such as [[http://love2d.org/][LÖVE]], [[http://pygame.org/][Pygame]], and [[http://pyglet.org/][Pyglet]]. Sly's functional reactive nature - is heavily inspired by the [[http://elm-lang.org/][Elm]] programming language. + library. Guile is no exception. Sly draws its inspiration from + easy-to-use libraries/engines such as [[http://love2d.org/][LÖVE]], [[http://pygame.org/][Pygame]], and [[http://pyglet.org/][Pyglet]]. + Sly's functional reactive nature is heavily inspired by the [[http://elm-lang.org/][Elm]] + programming language. ** Example @@ -31,17 +30,22 @@ #+BEGIN_SRC scheme (use-modules (sly game) - (sly sprite) - (sly window)) + (sly window) + (sly math vector) + (sly render camera) + (sly render group) + (sly render sprite)) - (define sprite - (load-sprite "images/p1_front.png" - #:position #(320 240))) + (define scene + (group-move (vector2 320 240) + (group (load-sprite "gnu.png")))) - (add-hook! draw-hook (lambda (dt alpha) (draw-sprite sprite))) + (define camera (orthographic-camera 640 480)) - (with-window (make-window #:title "Simple Sprite Demo") - (run-game-loop)) + (add-hook! draw-hook (lambda _ (draw-group scene camera))) + + (with-window (make-window #:title "Hello, world!") + (start-game-loop)) #+END_SRC ** Features @@ -68,164 +72,30 @@ (start-game-loop)) #+END_SRC -*** Sprites - - Sprites encapsulate the presentation of an image or a region of an - image. - - The simplest way to get started with sprites is to use the - =load-sprite= procedure. All arguments except the filename are - optional keyword arguments. - - Sly uses the FreeImage library and can load many different image - formats. See the FreeImage [[http://freeimage.sourceforge.net/features.html][features page]] for a full list of - supported formats. - - #+BEGIN_SRC scheme - (use-modules (sly sprite)) - - (define sprite - (load-sprite "cirno.png" - #:position #(320 240) - #:scale #(1 1) - #:rotation 45 - #:color white - #:anchor 'center)) - #+END_SRC - - Alternatively, you can make a sprite from an existing texture. The - same keyword arguments in =load-sprite= are also available here. - - #+BEGIN_SRC scheme - (define sprite (make-sprite (load-texture "cirno.png"))) - #+END_SRC - - Position, scale, rotation, color, and anchor are mutable. - - #+BEGIN_SRC scheme - (set-sprite-position! sprite #(100 100)) - #+END_SRC - - Drawing a sprite is simple. - - #+BEGIN_SRC scheme - (draw-sprite sprite) - #+END_SRC - -*** Keyboard and Mouse Input - - There are hooks within the =(sly keyboard)= and =(sly mouse)= - modules that can be used to respond to user input. - - #+BEGIN_SRC scheme - (use-modules (sly keyboard) - (sly mouse)) - - ;; Quit when ESC is pressed. - (add-hook! key-press-hook - (lambda (key unicode) - (when (eq? key 'escape) - (quit-game)))) - - ;; Print coordinates when the mouse is moved. - (add-hook! mouse-move-hook - (lambda (x y) - (format #t "pos: (~d, ~d)\n" x y))) - #+END_SRC - - In the future, there will be more convenient ways to respond to - user input similar to how keymaps work in Emacs. - -*** Coroutines and the Agenda - - The ability to write scripts is very important for most games. A - script for an RPG NPC could look like this: - - #+BEGIN_SRC scheme - ;; Walk up one tile and then down one tile, forever. - (while #t - (walk 'up) - (walk 'down)) - #+END_SRC - - Unfortunately, running this script as it is means completely - locking up the program in an unbounded loop. However, coroutines - (and a scheduler known as the "agenda") are here to save the day! - Coroutines are procedures that can be exited at any point and - resumed later. - - It would be nice if after every call to =walk=, the NPC would wait - for one second before taking its next step. This is where the - agenda comes in. The agenda is used to schedule procedures to be - run after an arbitrary number of game updates (1 by - default). Since coroutines and the agenda go hand in hand, there - exists a =wait= procedure to pause a coroutine and schedule it to - be resumed later. - - Using a coroutine and the agenda, the NPC script can be rewritten - such that it does not halt further program execution. - - #+BEGIN_SRC scheme - (use-modules (sly agenda) - (sly coroutine)) - - (coroutine - (while #t - (walk 'up) - (wait 60) - (walk 'down) - (wait 60))) - #+END_SRC - - =coroutine= is a useful macro that evaluates a block of code as a - coroutine. =wait= aborts the procedure and schedules the - continuation inside of the agenda. In this example, the script is - paused for 1 second after each step. Since Sly enforces a fixed - timestep and updates 60 times per second by default, 60 ticks is - equivalent to 1 second. - - You can also use the agenda to schedule the evaluation of any - thunk even if it isn't a coroutine. - - #+BEGIN_SRC scheme - (define (hello) - (display "Hello, world! Sorry I'm late!\n")) - - (schedule hello 600) - #+END_SRC - - =schedule= accepts a thunk (a procedure that takes no arguments) - and schedules it to be applied after a certain number of ticks, or - after 1 tick by default. In this example, the text "Hello, world! - Sorry I'm late!" is displayed after 10 seconds. There are other - ways to schedule procedures, too. =schedule-interval= applies a - thunk periodically, and =schedule-each= applies a thunk upon every - tick. - *** Functional Reactive Programming - Games are composed of values that evolve as time passes. The - player's score, the current stage, an enemy's hit points, etc. all - change in response to events that happen at discrete points in - time. Typically, this means that a number of callback procedures - are registered to react to events which mutate data structures - and/or assign to variables. However, this approach, while simple - and effective, comes at the price of readability and - comprehension. Instead of explicitly mutating data and entering - "callback hell", Sly abstracts and formalizes the process using a - functional reactive programming style. - - Time-varying values are called "signals", and they are created in - a declarative and functional manner. Rather than describing the - process of mutation procedurally, one describes the relationship - between signals instead. Signal relationships are described in a - functional style using =signal-map=, =signal-fold=, + Game state is a function of time. The player's score, the current + stage, an enemy's hit points, etc. all change in response to + events that happen at discrete points in time. Typically, this + means that a number of callback procedures are registered to + respond to events which mutate the relevant data structures. + However, this approach, while simple and effective, comes at the + price of readability, comprehension, and expression. Instead of + explicitly mutating data and entering "callback hell", Sly + abstracts and formalizes the process using a functional reactive + programming style. + + In Sly, time-varying values are called "signals", and they are + defined in a declarative and functional manner. Rather than + describing the process of mutation procedurally, one describes the + relationship between signals instead. Signal relationships are + described in a functional style using =signal-map=, =signal-fold=, =signal-filter=, and others. Example: #+BEGIN_SRC scheme (define-signal position - (signal-fold v+ #(320 240) + (signal-fold v+ (vector2 320 240) (signal-map (lambda (v) (v* v 4)) (signal-sample 1 key-arrows)))) #+END_SRC @@ -235,7 +105,7 @@ to trigger a signal update upon every game tick that provides the current state of the arrow keys. =key-arrows= is a vector that maps to the current state of the arrow keys, allowing for 8 - direction movement. This vector is then scaled 4x to make the + directional movement. This vector is then scaled 4x to make the player move faster. Finally, the scaled vector is added to the previous player position via =signal-fold=. The player's position is at (320, 240) initially. As you can see, there are no @@ -250,15 +120,15 @@ *** REPL Driven Development - The read-eval-print-loop present in Guile allows you to develop - your game while it is running! This allows you to see in real time - what your changes do to the game without having to restart the - program every time. + Guile's read-eval-print-loop allows you to develop your game while + it is running! This allows you to see in real-time what your + changes do to the game without having to kill, recompile, and + restart the program every time a change is made. - Sly integrates Guile's cooperative REPL server with the game loop. + Sly integrates Guile's [[https://gnu.org/software/guile/manual/html_node/Cooperative-REPL-Servers.html][cooperative REPL server]] into the game loop. To activate this feature, import the =(sly repl)= module and call =(start-sly-repl)=. To connect to the REPL server, use the [[http://www.nongnu.org/geiser/][Geiser]] - extension for GNU Emacs or telnet. + extension for GNU Emacs. *Geiser* @@ -266,13 +136,7 @@ M-x connect-to-guile #+END_SRC - Use the default host and port settings. - - *Telnet* - - #+BEGIN_SRC sh - telnet localhost 37146 - #+END_SRC + Use the default host and port settings when prompted. ** Building @@ -337,6 +201,7 @@ - [[https://www.gnu.org/software/guile-sdl/index.html][guile-sdl]] >= 0.5.0 - SDL 1.2 - FreeImage >= 3.0 + - GNU Scientific Library (GSL) ** Community |