For clouds, use a RNG seed that only changes every 10 minutes.

This allows multi-process deploymentes to keep their clouds in sync.

simgear/math/sg_random.c

@@ -59,6 +59,11 @@ void mt_init(mt *mt, unsigned int seed)
     mt->index = MT_N+1;
 }
 
+void mt_init_time_10(mt *mt)
+{
+  mt_init(mt, (unsigned int) time(NULL) / 600);  
+}
+
 unsigned int mt_rand32(mt *mt)
 {
     unsigned int i, y;

simgear/math/sg_random.h

@@ -47,6 +47,13 @@ typedef struct {unsigned int array[MT_N]; int index; } mt;
  */
 void mt_init(mt *mt, unsigned int seed);
 
+/**
+ * Initialize a new MT state with a seed that only
+ * changes every 10 minutes.  Used to synchronize
+ * multi-process deployments.
+ */
+void mt_init_time_10(mt *mt);
+
 /**
  * Generate a new 32-bit random number based on the given MT state.
  */