Engine directory for ticket #1

Engine/source/math/mRandomSet.h

@@ -0,0 +1,93 @@
+//-----------------------------------------------------------------------------
+// Copyright (c) 2012 GarageGames, LLC
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to
+// deal in the Software without restriction, including without limitation the
+// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+// sell copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+// IN THE SOFTWARE.
+//-----------------------------------------------------------------------------
+
+#ifndef _MRANDOMSET_H_
+#define _MRANDOMSET_H_
+
+#ifndef _MRANDOM_H_
+#include "math/mRandom.h"
+#endif
+
+template <class T>
+class MRandomSet
+{
+protected:
+
+   MRandomLCG *mRandGen;
+
+   Vector<T> mItems;
+   Vector<F32> mProbability;
+   F32 mSum;
+
+public:
+
+   MRandomSet( MRandomLCG *randGen = &gRandGen );
+
+   void add( const T &item, F32 probability );
+   
+   /// Return a random item from the set using the specified per
+   /// item probability distribution.
+   T get();
+};
+
+template<class T>
+inline MRandomSet<T>::MRandomSet( MRandomLCG *randGen )
+ : mRandGen( randGen ),
+   mSum( 0.0f )
+{
+}
+
+template<class T> 
+inline void MRandomSet<T>::add( const T &item, F32 probability )
+{
+   AssertFatal( probability > 0.0f, "MRandomDeck - item probability must be positive." );
+
+   mItems.push_back( item );
+   mProbability.push_back( probability );
+   mSum += probability;
+}
+
+template<class T> 
+inline T MRandomSet<T>::get()
+{ 
+   AssertFatal( mSum > 0.0f, "MRandomDeck - no items to get." );
+
+   F32 rand = mRandGen->randF(0.0f, mSum);
+
+   F32 prev = -1.0f;
+   F32 curr = 0.0f;
+
+   for ( S32 i = 0; i < mItems.size(); i++ )
+   {
+      curr += mProbability[i];
+
+      if ( rand > prev && rand <= curr )
+         return mItems[i];
+         
+      prev = curr;
+   }
+   
+   AssertFatal( false, "MRandomSet::get() has failed." );
+   return NULL;
+}
+
+#endif //_MRANDOMSET_H_