inheritance and polymorphism issue

[sajis997]

Hello forum,

I believe that i have the design problem that i need to discuss about.

Intersectable is the super-class; Triangle and Sphere are the sub-classes of the Intersectable

i believe that you already realized class inheritance structure. I have the following pure virtual functions declared inside the INTERSECTABLE

   virtual bool sampleDirection(const Intersection&,Vector3D&) = 0;

   virtual float getPDF(const Intersection&,
			const Intersection&) = 0;

Each of the sub-classes are defining the above functions.

There is another class called AreaLight that contains a std::vector as follows:

   class LuminaireProbability
   {
   public:

       LuminaireProbability() : mIntersectable(0),mMaterial(0),mLuminaireProbabilityValue(0.0f),
           mCumulativeDistributionValue(0.0f)
       {
       }

       ~LuminaireProbability()
       {
           mIntersectable = 0;
           mMaterial = 0;
       }

      //luminaire as an intersectable
      Intersectable *mIntersectable;
      //material of the intersectable
      Material *mMaterial;
      //probability of choosing the luminaire
      float mLuminaireProbabilityValue;

      //cumulative distribution value
      float mCumulativeDistributionValue;

   };

   //the area light contains the reference
   //to the geometric object to be the light source
   //the geometric object in turn contains the emissive material
   //thus providing the illumination
   //in this way the type of geometric object automatically determines
   //the type of light, in principle it allows any type of the geometric
   //object to be a light source
   //SOME OF THE ABOVE STATEMENTS DEMANS CHANGE
   std::vector<LuminaireProbability*> mLightIntersectables;

   //store the selected lumianire from the vector
   LuminaireProbability *mSelectedLuminaire;

I have the std::vector populated with a pointer of intersectables of type triangle or sphere along with some other trivial information. Now i have the following function

//calcualate the world position based on the intersection point
bool AreaLight::calculateSampleDirection(const Intersection &intersection,Vector3D &sampleVector)
{

   //choose the light intersectables based on the weight of the probaiblity
   //that we have calculated in the prepare() function

   float selectionProbability = 0.0f;

   //create a random instance
   RandomGenerator random = RandomGenerator::getRandomInstance();

   //create a canonical random number between 0 and 1
   selectionProbability = static_cast<float>(random.generateDouble(0,1));

   CompareToCDF cdf;
   //store the canonical random value
   cdf.mRandomValue = selectionProbability;

//   CompareAreaLight cmpAreaLight;

//   //sort the light intersectables based on the luminaire probability value
//   std::sort(mLightIntersectables.begin(),mLightIntersectables.end(),cmpAreaLight);

   std::vector<LuminaireProbability*>::iterator it;

   it = std::find_if(mLightIntersectables.begin(),mLightIntersectables.end(),cdf);

   assert(it != mLightIntersectables.end());

   //store the selected luminaire
   mSelectedLuminaire = *it;

   //I AM GETTING A SEGMENTATION FAULT IN THE FOLLOWING FUNCTION - !!!!!
   mSelectedLuminaire->mIntersectable->sampleDirection(intersection,sampleVector);

   return true;
}

As mentioned in the code i am getting the segmentation fault that the debugger is not even giving any hint of.


I hope you will be able to help me find out the issue here that i am missing.
Is there any logical mistake i am doing here?


Regards
Sajjad

[Computergeek01]

Obviously you have a pretty complex program here, so it would be difficult if not impossible for anyone to diagnose the issue with only what you gave us. But if I had to guess, I would say that since your constructor sets all of your pointers to 0 that one of the objects being referenced is still pointing to a NULL value. Maybe temporarily try something like:

if(mSelectedLuminaire != NULL)
{
    if(mSelectedLuminaire->mIntersectable != NULL(
    {
         //code code code 
    }
}

[sajis997]

Thanks for the hint. I tried as follows:

   if(mSelectedLuminaire != 0)
    {
       if(mSelectedLuminaire->mIntersectable != 0)
        //SEGMENTATION FAULT!!!
        mSelectedLuminaire->mIntersectable->sampleDirection(intersection,sampleVector);
    }

Still i am getting the segmentation fault with the function as before.

Any where to look into?

Regards
Sajjad

[Computergeek01]

Just so that we know for sure, would you mind copy and pasting the error that you are getting?

[sajis997]

Hi again,

I get the following while running the application:

Path tracing...
[New Thread 0xb517bb40 (LWP 4525)]
[New Thread 0xb497ab40 (LWP 4526)]
[New Thread 0xb4179b40 (LWP 4527)]
[New Thread 0xb3978b40 (LWP 4528)]
[New Thread 0xb3177b40 (LWP 4529)]
[New Thread 0xb2976b40 (LWP 4530)]
[New Thread 0xb2175b40 (LWP 4531)]

Program received signal SIGSEGV, Segmentation fault.
0x2efd85ba in ?? ()

And then i tried to run with GDB, did the backtrace and then i get the following :

(gdb) backtrace
#0  0x2efd85ba in ?? ()
#1  0x0804e018 in AreaLight::calculateSampleDirection (this=0x80c4d60, 
    intersection=..., sampleVector=...) at arealight.cpp:151
#2  0x080556ed in Intersection::getShadowRay (this=0xbfffedfc, light=0x80c4d60)
    at intersection.cpp:152
#3  0x08069787 in PathTracer::computeDirectIllumination (this=0xbffff220, 
    intersection=...) at pathtracer.cpp:179
#4  0x0806a3df in PathTracer::computeRadiance (this=0xbffff220, 
    intersection=..., depth=5) at pathtracer.cpp:141
#5  0x0806a63f in PathTracer::trace (this=0xbffff220, ray=..., E=1)
    at pathtracer.cpp:127
#6  0x0806a8e0 in PathTracer::tracePixel (this=0xbffff220, x=0, y=1)
    at pathtracer.cpp:95
#7  0x0806aa14 in PathTracer::computeImage() [clone ._omp_fn.0] ()
    at pathtracer.cpp:53
#8  0x0806ac46 in PathTracer::computeImage (this=0xbffff220)
    at pathtracer.cpp:47
#9  0x0804c397 in main (argc=1, argv=0xbffff304) at main.cpp:504
(gdb) 

Please let me know if there is any more information i can provide you with to help me get around with this issue.

Thanks
Sajjad

[Computergeek01]

Are you using multiple threads or am I reading that wrong? Maybe something is over-writing\deleting one of your const references while another thread is trying to use it?

[sajis997]

I am not using any multi-threading over here. Where do think i am deleting stuff in the code i have provided with you so far.

I am just cleaning the memory occupied in the std::vector in the destructor for the AreaLight as follows:

AreaLight::~AreaLight()
{
   //empty the vector
    for(unsigned int i = 0; i < mLightIntersectables.size();++i)
    {
        delete mLightIntersectables[i];
        mLightIntersectables[i] = 0;
    }

   mLightIntersectables.clear();

   if(mSelectedLuminaire != 0)
   {
       delete mSelectedLuminaire;
       mSelectedLuminaire = 0;
   }
 
}

Anything more ?