Implement auto-adjusting of particle emit rate

This makes ashcloud.nif and blightcloud.nif work properly.

components/nif/controller.hpp

@@ -89,7 +89,14 @@ public:
     float lifetime;
     float lifetimeRandom;
 
-    int emitFlags; // Bit 0: Emit Rate toggle bit (0 = auto adjust, 1 = use Emit Rate value)
+    enum EmitFlags
+    {
+        NoAutoAdjust = 0x1 // If this flag is set, we use the emitRate value. Otherwise,
+                           // we calculate an emit rate so that the maximum number of particles
+                           // in the system (numParticles) is never exceeded.
+    };
+    int emitFlags;
+
     Ogre::Vector3 offsetRandom;
 
     NodePtr emitter;

components/nifogre/ogrenifloader.cpp

@@ -756,7 +756,12 @@ class NIFObjectLoader
         Ogre::ParticleEmitter *emitter = partsys->addEmitter("Nif");
         emitter->setParticleVelocity(partctrl->velocity - partctrl->velocityRandom*0.5f,
                                      partctrl->velocity + partctrl->velocityRandom*0.5f);
-        emitter->setEmissionRate(partctrl->emitRate);
+
+        if (partctrl->emitFlags & Nif::NiParticleSystemController::NoAutoAdjust)
+            emitter->setEmissionRate(partctrl->emitRate);
+        else
+            emitter->setEmissionRate(partctrl->numParticles / (partctrl->lifetime + partctrl->lifetimeRandom/2));
+
         emitter->setTimeToLive(partctrl->lifetime,
                                partctrl->lifetime + partctrl->lifetimeRandom);
         emitter->setParameter("width", Ogre::StringConverter::toString(partctrl->offsetRandom.x));