OpenSceneGraph/src/osg/ShadowVolumeOccluder.cpp

#include <osg/ShadowVolumeOccluder>
#include <osg/CullStack>

using namespace osg;



typedef std::pair<bool,Vec3>    Point; // bool=true signifies a newly created point, false indicates original point.
typedef std::vector<Point>      PointList;
typedef std::vector<Vec3>       VertexList;


// convert a vector for Vec3 into a vector of Point's.
void convert(const VertexList& in,PointList& out)
{
    out.reserve(in.size());
    for(VertexList::const_iterator itr=in.begin();
        itr!=in.end();
        ++itr)
    {
        out.push_back(Point(false,*itr));
    }
}

// clip the convex hull 'in' to plane to generate a clipped convex hull 'out'
// return true if points remain after clipping.
unsigned int clip(const Plane& plane,const PointList& in, PointList& out)
{
    std::vector<float> distance;
    distance.reserve(in.size());
    for(PointList::const_iterator itr=in.begin();
        itr!=in.end();
        ++itr)
    {
        distance.push_back(plane.distance(itr->second));
    }

    out.clear();

    for(unsigned int i=0;i<in.size();++i)
    {
        unsigned int i_1 = (i+1)%in.size(); // do the mod to wrap the index round back to the start.
        
        if (distance[i]>=0.0f)
        {
            out.push_back(in[i]);
            
            if (distance[i_1]<0.0f)
            {
                float r = distance[i_1]/(distance[i_1]-distance[i]);
                out.push_back(Point(true,in[i].second*r+in[i_1].second*(1.0f-r)));
            }
        
        }
        else if (distance[i_1]>0.0f)
        {
            float r = distance[i_1]/(distance[i_1]-distance[i]);
            out.push_back(Point(true,in[i].second*r+in[i_1].second*(1.0f-r)));
        }
    }
    
    return out.size();
}

// clip the convex hull 'in' to planeList to generate a clipped convex hull 'out'
// return true if points remain after clipping.
unsigned int clip(const Polytope::PlaneList& planeList,const VertexList& vin,PointList& out)
{
    PointList in;
    convert(vin,in);
    
    for(Polytope::PlaneList::const_iterator itr=planeList.begin();
        itr!=planeList.end();
        ++itr)
    {
        if (!clip(*itr,in,out)) return false;
        in.swap(out);
    }

    in.swap(out);

    return out.size();
}

void transform(PointList& points,const osg::Matrix& matrix)
{
    for(PointList::iterator itr=points.begin();
        itr!=points.end();
        ++itr)
    {
        itr->second = itr->second*matrix;
    }
}

void transform(const PointList& in,PointList& out,const osg::Matrix& matrix)
{
    for(PointList::const_iterator itr=in.begin();
        itr!=in.end();
        ++itr)
    {
        out.push_back(Point(itr->first,itr->second * matrix));
    }
}

void pushToFarPlane(PointList& points)
{
    for(PointList::iterator itr=points.begin();
        itr!=points.end();
        ++itr)
    {
        itr->second.z()=-1.0f;
    }
}

void computePlanes(const PointList& front, const PointList& back, Polytope::PlaneList& planeList)
{
    for(unsigned int i=0;i<front.size();++i)
    {
        unsigned int i_1 = (i+1)%front.size(); // do the mod to wrap the index round back to the start.
        if (!front[i].first || !front[i_1].first)
        {
            planeList.push_back(Plane(front[i].second,front[i_1].second,back[i].second));
        }
    }
}

Plane computeFrontPlane(const PointList& front)
{
    return Plane(front[2].second,front[1].second,front[0].second);
}

bool ShadowVolumeOccluder::computeOccluder(const NodePath& nodePath,const ConvexPlanerOccluder& occluder,CullStack& cullStack)
{


//    std::cout<<"    Computing Occluder"<<std::endl;

    CullingSet& cullingset = cullStack.getCurrentCullingSet();

    const Matrix& MV = cullStack.getModelViewMatrix();
    const Matrix& P = cullStack.getProjectionMatrix();

    // take a reference to the NodePath to this occluder.
    _nodePath = nodePath;
    

    // take a reference to the projection matrix.
    _projectionMatrix = &P;
    
    

    // compute the inverse of the projection matrix.
    Matrix invP;
    invP.invert(P);
    
    // compute the transformation matrix which takes form local coords into clip space.
    Matrix MVP(MV);
    MVP *= P;
    
    // for the occluder polygon and each of the holes do
    //     first transform occluder polygon into clipspace by multiple it by c[i] = v[i]*(MV*P)
    //     then push to coords to far plane by setting its coord to c[i].z = -1.
    //     then transform far plane polygon back into projection space, by p[i]*inv(P)
    //     compute orientation of front plane, if normal.z()<0 then facing away from eye pont, so reverse the polygons, or simply invert planes.
    //     compute volume (quality) betwen front polygon in projection space and back polygon in projection space.
    
    
    const VertexList& vertices_in = occluder.getOccluder().getVertexList();
    
    PointList points;
    
    if (clip(cullingset.getFrustum().getPlaneList(),vertices_in,points)>=3)
    {
        // compute the points on the far plane.
        PointList farPoints;
        farPoints.reserve(points.size());
        transform(points,farPoints,MVP);
        pushToFarPlane(farPoints);
        transform(farPoints,invP);
        
        // move the occlude points into projection space.
        transform(points,MV);

        // create the sides of the occluder
        computePlanes(points,farPoints,_occluderVolume.getPlaneList());

        // create the front face of the occluder
        Plane occludePlane = computeFrontPlane(points);
        _occluderVolume.add(occludePlane);
        
        // if the front face is pointing away from the eye point flip the whole polytope.
        if (occludePlane[3]>0.0f)
        {
//            std::cout << "    flipping polytope"<<std::endl;
            _occluderVolume.flip();
        }
        
        
        for(Polytope::PlaneList::const_iterator itr=_occluderVolume.getPlaneList().begin();
            itr!=_occluderVolume.getPlaneList().end();
            ++itr)
        {
//            std::cout << "    compute plane "<<*itr<<std::endl;
        }


        return true;
    }
    else
    {
//        std::cout << "    occluder clipped out of frustum."<<points.size()<<std::endl;
        return false;
    }
}

bool ShadowVolumeOccluder::contains(const std::vector<Vec3>& vertices)
{
    if (_occluderVolume.containsAllOf(vertices))
    {
        for(HoleList::iterator itr=_holeList.begin();
            itr!=_holeList.end();
            ++itr)
        {
            if (itr->contains(vertices)) return false;
        }
        return true;
    }
    return false;
}

bool ShadowVolumeOccluder::contains(const BoundingSphere& bound)
{
    if (_occluderVolume.containsAllOf(bound))
    {
        for(HoleList::iterator itr=_holeList.begin();
            itr!=_holeList.end();
            ++itr)
        {
            if (itr->contains(bound)) return false;
        }
        return true;
    }
    return false;
}

bool ShadowVolumeOccluder::contains(const BoundingBox& bound)
{
    if (_occluderVolume.containsAllOf(bound))
    {
        for(HoleList::iterator itr=_holeList.begin();
            itr!=_holeList.end();
            ++itr)
        {
            if (itr->contains(bound)) return false;
        }
        return true;
    }
    return false;
}