Add script scheduler and pre/post visual effects system.

modules/game/effects.scm

@@ -0,0 +1,76 @@
+(define-module (game effects)
+  #:use-module (dom canvas)
+  #:use-module (ice-9 match)
+  #:use-module (math)
+  #:use-module (srfi srfi-9)
+  #:use-module (scheme time)
+  #:export (ease:smoothstep
+            ease:linear
+
+            make-effect
+            effect?
+            effect-started?
+            effect-type
+            effect-duration
+            effect-start!
+            draw-effect
+
+            make-fade-out+in-effect
+            make-screen-shake-effect))
+
+(define (ease:smoothstep t)
+  (* t t (- 3 (* 2 t))))
+
+(define (ease:linear t) t)
+
+(define (current-time*)
+  (/ (exact->inexact (current-jiffy)) (jiffies-per-second)))
+
+(define-record-type <effect>
+  (%make-effect type draw ease duration start)
+  effect?
+  (type effect-type)
+  (draw effect-draw)
+  (ease effect-ease)
+  (duration effect-duration)
+  (start effect-start set-effect-start!))
+
+(define* (make-effect type duration draw #:optional (ease ease:smoothstep))
+  (%make-effect type draw ease duration #f))
+
+(define (effect-started? effect)
+  (number? (effect-start effect)))
+
+(define (effect-start! effect)
+  (set-effect-start! effect (current-time*)))
+
+(define (draw-effect context effect)
+  (match effect
+    (($ <effect> type draw ease duration start)
+     (when (number? start)
+       (let ((dt (- (current-time*) start)))
+         (if (>= dt duration)
+             (set-effect-start! effect #f)
+             (let ((t (ease (/ dt duration))))
+               (draw context t))))))))
+
+;; Duplicated from game.scm but gotta go fast!!
+(define game-width 320.0)
+(define game-height 240.0)
+
+(define (make-fade-out+in-effect duration)
+  (define (draw context t)
+    (if (< t 0.5)
+        (set-global-alpha! context (pk 'alpha-out (* t 2.0)))
+        (set-global-alpha! context (pk 'alpha-in (- 1.0 (* (- t 0.5) 2.0)))))
+    (set-fill-color! context "#000000")
+    (fill-rect context 0.0 0.0 game-width game-height)
+    (set-global-alpha! context 1.0))
+  (make-effect 'post duration draw))
+
+(define (make-screen-shake-effect duration)
+  (define (draw context t)
+    (let ((x (round (random)))
+          (y (round (random))))
+      (translate! context x y)))
+  (make-effect 'pre duration draw))