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| -rw-r--r-- | README.org | 168 |
1 files changed, 131 insertions, 37 deletions
@@ -21,45 +21,139 @@ Here is the simplest Guile-2d application (so far). #+BEGIN_SRC scheme - (use-modules (figl gl) - (2d sprite) - (2d game-loop) - (2d window) - (2d input)) - - (define window-width 800) - (define window-height 600) - (define sprite #f) - - (define (key-down key) - (display key) (newline) - (case key - ;; Quit program when ESCAPE or Q is pressed. - ((any-equal? key (keycode escape) (keycode q)) - (close-window) - (quit)))) - - ;; Draw our sprite - (define (render) - (draw-sprite sprite)) - - ;; Register callbacks. - (set-render-callback (lambda () (render))) - (set-key-down-callback (lambda (key) (key-down key))) - - ;; Open the window. - (open-window window-width window-height) - - ;; Load a sprite and center it on the screen. - ;; Must be done AFTER opening the window. - (set! sprite (load-sprite "sprite.png" #:position (vector (/ window-width 2) - (/ window-height 2)))) - - ;; Start the game loop. - ;; The render callback will be called through this procedure. - (run-game-loop) + (use-modules (figl gl) + (2d sprite) + (2d game-loop) + (2d window) + (2d input)) + + (define window-width 800) + (define window-height 600) + (define sprite #f) + + (define (key-down key) + (display key) (newline) + (case key + ;; Quit program when ESCAPE or Q is pressed. + ((any-equal? key (keycode escape) (keycode q)) + (close-window) + (quit)))) + + ;; Draw our sprite + (define (render) + (draw-sprite sprite)) + + ;; Register callbacks. + (set-render-callback (lambda () (render))) + (set-key-down-callback (lambda (key) (key-down key))) + + ;; Open the window. + (open-window window-width window-height) + + ;; Load a sprite and center it on the screen. + ;; Must be done AFTER opening the window. + (set! sprite (load-sprite "sprite.png" #:position (vector (/ window-width 2) + (/ window-height 2)))) + + ;; Start the game loop. + ;; The render callback will be called through this procedure. + (run-game-loop) #+END_SRC +** Features + +*** Sprites + Sprites encapsulate the presentation of a 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. + + #+BEGIN_SRC scheme + (define sprite (load-sprite "cirno.png" #:position #(0 0) #:scale (1 1) + #:rotation (0) #:color #xffffff #: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 texture + (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 + +*** Sprite Batches + When drawing many sprites, it is inefficient to send them to the + GPU individually. Sprite batches resolve this issue by sending + sprites to the GPU in large chunks. + + To take advantage of this, create a sprite batch and use + `with-sprite-batch`. All calls to `draw-sprite` will use the + sprite batch within this form. + + #+BEGIN_SRC scheme + (define sprites (make-a-ton-of-sprites)) + + (define batch (make-sprite-batch)) + + (with-sprite-batch batch + (for-each + (lambda (sprite) (draw-sprite sprite)) + sprites)) + #+END_SRC + +*** Coroutines and Agendas + 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 + (while #t + (walk 'up) + (wait 60) + (walk 'down) + (wait 60)) + #+END_SRC + + Since guile-2d enforces a fixed timestep and updates 60 times per + second, waiting for 60 updates means that the NPC will wait one + second in between each step. + ** 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 |