From c62dceb1471afb94efa57eef5506fbdf6f2ef679 Mon Sep 17 00:00:00 2001
From: Javier Sancho <jsf@jsancho.org>
Date: Sun, 8 Dec 2013 07:11:34 +0100
Subject: [PATCH] Set engine systems while running

* src/engine.scm: new function set-engine-systems! using engine mutex
                  for avoiding concurrency errors

* src/system.scm: new function group-systems, that returns joined
                  systems or an empty system, depending on arguments
---
 src/engine.scm | 11 +++++++----
 src/system.scm | 11 ++++++++++-
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/src/engine.scm b/src/engine.scm
index 4e311a0..33c8a6f 100644
--- a/src/engine.scm
+++ b/src/engine.scm
@@ -50,9 +50,7 @@
      (list e c))
    (make-mutex)
    (make-mutex)
-   (if (not (= (length systems) 1))
-       (join-systems systems)
-       (car systems))))
+   (apply group-systems systems)))
 
 (define-syntax define-engine
   (syntax-rules ()
@@ -122,6 +120,10 @@
 	 (set-current-engine! old-engine)
 	 res)))))
 
+(define (set-engine-systems! engine . systems)
+  (with-mutex (engine-mutex engine)
+    (set-engine-system! engine (apply group-systems systems))))
+
 (export current-engine
 	set-current-engine!
 	get-entity
@@ -131,7 +133,8 @@
 	set-entity!
 	set-entity-components!
 	remove-entity-components!
-	with-engine)
+	with-engine
+	set-engine-systems!)
 
 
 ;;; Engine execution
diff --git a/src/system.scm b/src/system.scm
index 3d5cb2b..2bf0520 100644
--- a/src/system.scm
+++ b/src/system.scm
@@ -247,11 +247,20 @@
 	     (receive (e2 c2) ((join-thread (car thd)) e c)
 	       (run-wait (cdr thd) e2 c2)))))))
 
+(define (group-systems . systems)
+  (cond ((null? systems)
+	 (make-system ()))
+	((= (length systems) 1)
+	 (car systems))
+	(else
+	 (join-systems systems))))
+
 (export find-entities-by-components
 	define-system
 	make-system
 	join-systems
-	threaded-systems)
+	threaded-systems
+	group-systems)
 
 
 ;;; Entities and components access inside systems
-- 
2.39.2