--- ray/src/rt/pmaprand.h	2015/02/24 19:39:27	2.1
+++ ray/src/rt/pmaprand.h	2024/09/17 16:36:05	2.9
@@ -1,34 +1,60 @@
-#ifndef PMAPRAND_H
-#define PMAPRAND_H
+/* RCSid $Id: pmaprand.h,v 2.9 2024/09/17 16:36:05 greg Exp $ */
 
 /* 
-   ==================================================================
+   ======================================================================
    Random number generators for photon distribution
 
    Roland Schregle (roland.schregle@{hslu.ch, gmail.com})
    (c) Fraunhofer Institute for Solar Energy Systems,
-       Lucerne University of Applied Sciences & Arts
-   ==================================================================
+   (c) Lucerne University of Applied Sciences and Arts,
+       supported by the Swiss National Science Foundation (SNSF, #147053)
+   ======================================================================
    
-   $Id: pmaprand.h,v 2.1 2015/02/24 19:39:27 greg Exp $
+   $Id: pmaprand.h,v 2.9 2024/09/17 16:36:05 greg Exp $
 */
 
 
 
-/* According to the analytical validation, skipping numbers in the sequence
-   introduces bias in scenes with high reflectance. We therefore use
-   erand48() with separate states for photon emission, scattering, and
-   russian roulette. The pmapSeed() and pmapRandom() macros can be adapted
-   to other (better?) RNGs. */   
-   
-#define pmapSeed(seed, state) (state [0] += seed, state [1] += seed, \
-                               state [2] += seed)
-#define pmapRandom(state) erand48(state)
+#ifndef PMAPRAND_H
+   #define PMAPRAND_H
 
+   /* According to the analytical validation, skipping sequential samples
+    * when sharing a single RNG among multiple sampling domains introduces
+    * overlapping photon rays (reported as 'duplicate keys' when building
+    * the underlying data structure) and therefore bias.  This is aggravated
+    * when running parallel photon distribution subprocesses, where photon
+    * rays from different subprocesses may correlate.    
+    * We therefore maintain a separate RNG state for each sampling domain
+    * (e.g. photon emission, scattering, and russian roulette).  With
+    * multiprocessing, each subprocess has its own instance of the RNG
+    * state, which is independently seeded for decorellation -- see
+    * distribPhotons() and distribPhotonContrib().    
+    * The pmapSeed() and pmapRandom() macros below can be adapted to
+    * platform-specific RNGs if necessary.  */
+#if defined(_WIN32) || defined(_WIN64)
+   /* Use standard RNG without state management; the generated sequences
+    * will be suboptimal */
+   #include "random.h"      
+   #define pmapSeed(seed, state) srandom(seed)
+   #define pmapRandom(state)     frandom()
+#else
+   /* Assume NIX and manage RNG state via erand48() */
+   #define pmapSeed(seed, state) (state [0] += seed, state [1] += seed, \
+                                  state [2] += seed)
+   #define pmapRandom(state)     erand48(state)
+#endif
 
-   
-extern unsigned short partState [3], emitState [3], cntState [3],
-                      mediumState [3], scatterState [3], rouletteState [3],
-                      randSeed;
+#ifdef __cplusplus
+extern "C" {
+#endif
+      
+   extern unsigned short partState [3], emitState [3], cntState [3],
+                         mediumState [3], scatterState [3], rouletteState [3],
+                         randSeed;
+                         
+#ifdef __cplusplus
+}
+#endif
 
 #endif
+