From 2e354c9e235b382c1870dcaad166b846dbc7287e Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Wed, 12 Sep 2018 17:58:21 -0400
Subject: Add support for transitions in sequence scene.

---
 starling/transition.scm | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/starling/transition.scm b/starling/transition.scm
index 826032e..3a544f9 100644
--- a/starling/transition.scm
+++ b/starling/transition.scm
@@ -32,6 +32,8 @@
   #:use-module (starling scene)
   #:export (<sequence-scene>
             scenes
+            last-scene
+            transition
 
             <transition>
             scene-from
@@ -49,16 +51,31 @@
 ;; transitioning scenes.
 
 (define-class <sequence-scene> (<scene>)
-  (scenes #:accessor scenes #:init-keyword #:scenes))
+  (scenes #:accessor scenes #:init-keyword #:scenes)
+  (last-scene #:accessor last-scene #:init-form #f)
+  (transition #:accessor transition #:init-keyword #:transition
+              #:init-form default-sequence-transition))
+
+(define (default-sequence-transition from to)
+  ;; Return the 'to' scene as-is, which means there is no transition
+  ;; at all.
+  to)
 
 (define-method (on-enter (sequence <sequence-scene>))
+  (define (next-scene-transition scene)
+    (let ((last (last-scene sequence)))
+      (if last
+          ((transition sequence) last scene)
+          scene)))
   (match (scenes sequence)
     ((scene)
      ;; If we've reached the last scene, we're done!
-     (replace-scene scene))
+     (replace-scene (next-scene-transition scene)))
     ((scene . rest)
-     (set! (scenes sequence) rest)
-     (push-scene scene))))
+     (let ((next-scene (next-scene-transition scene)))
+       (set! (scenes sequence) rest)
+       (set! (last-scene sequence) scene)
+       (push-scene next-scene)))))
 
 
 ;;;
-- 
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