source: GTP/trunk/App/Demos/Vis/FriendlyCulling/src/Polygon3.cpp @ 2913

#include "Polygon3.h"
#include "AxisAlignedBox3.h"
#include "Plane3.h"


using namespace std;

namespace CHCDemoEngine 
{

Polygon3::Polygon3()
{
}


Polygon3::Polygon3(const VertexArray &vertices)
{
        mVertices.reserve(vertices.size());
        mVertices = vertices;
}


Polygon3::~Polygon3() 
{
}


Plane3 Polygon3::GetSupportingPlane() const
{
        return Plane3(mVertices[0], mVertices[1], mVertices[2]);
}


Vector3 Polygon3::GetNormal() const 
{
    return Normalize(CrossProd(mVertices[2] - mVertices[1],
                                                           mVertices[0] - mVertices[1]));
}


void Polygon3::Split(const Plane3 &partition, 
                                         Polygon3 &front, 
                                         Polygon3 &back, float epsilon)
{
        Vector3 ptA = mVertices.back();
        int sideA = partition.Side(ptA, epsilon);
        bool foundSplit = false;
    Vector3 lastSplit;
                
        /////////////
        //-- find line - plane intersections

        VertexArray::const_iterator it, it_end = mVertices.end();

        for (it = mVertices.begin(); it != it_end; ++ it)
        {
                Vector3 ptB = *it;
                int sideB = partition.Side(ptB, epsilon);
        
                // vertices on different sides => split
            if (sideB > 0)
                {
                        if (sideA < 0)
                        {
                                //-- plane - line intersection
                                Vector3 splitPt = partition.FindIntersection(ptA, ptB);
                        
                                // test if split point not too close to previous split point
                                if (!foundSplit || (!EpsilonEqualV3(splitPt, lastSplit, epsilon)))
                                {
                                        // add vertex to both polygons
                                        front.mVertices.push_back(splitPt);
                                        back.mVertices.push_back(splitPt);
                                        
                                        lastSplit = splitPt;
                                        foundSplit = true;
                                }
                        }
                        front.mVertices.push_back(ptB);
                }
                else if (sideB < 0)
                {
                        if (sideA > 0)
                        {
                                ////////////
                                //-- plane - line intersection

                                Vector3 splitPt = partition.FindIntersection(ptA, ptB);
                                
                                // test if split point not too close to previous split point
                                if (!foundSplit || (!EpsilonEqualV3(splitPt, lastSplit, epsilon)))
                                {
                                        // add vertex to both polygons
                                        front.mVertices.push_back(splitPt);
                                        back.mVertices.push_back(splitPt);

                                        lastSplit = splitPt;
                                        foundSplit = true;
                                }       
                        }

                        back.mVertices.push_back(ptB);
                }
                else
                {
                        // vertex on plane => add vertex to both polygons
                        front.mVertices.push_back(ptB);
                        back.mVertices.push_back(ptB); 
                }
        
                ptA = ptB;
                sideA = sideB;
        }
}


float Polygon3::GetArea() const
{
        Vector3 v = CrossProd(mVertices.back(), mVertices.front());
    
    for (int i=0; i < mVertices.size() - 1; ++i)
                v += CrossProd(mVertices[i], mVertices[i+1]);
    
    return 0.5f * fabs(DotProd(GetNormal(), v));
}


int Polygon3::Side(const Plane3 &plane, 
                                   const float epsilon) const
{
        int classification = ClassifyPlane(plane, epsilon);
        
        if (classification == BACK_SIDE)
                return -1;
        else if (classification == FRONT_SIDE)
                return 1;

        // plane splits polygon or is coincident
        return 0;
}


int Polygon3::ClassifyPlane(const Plane3 &plane, 
                                                        const float epsilon) const
{
        VertexArray::const_iterator it, it_end = mVertices.end();

        bool onFrontSide = false;
        bool onBackSide = false;
        
        int count = 0;
        // find possible line-plane intersections
        for (it = mVertices.begin(); it != it_end; ++ it)
        {
                const int side = plane.Side(*it, epsilon);
                
                if (side > 0)
                {
                        onFrontSide = true;
                }
                else if (side < 0)
                {
                        onBackSide = true;
                }

                //TODO: check if split goes through vertex
                if (onFrontSide && onBackSide) // split 
                {
                        return SPLIT;
                }
                // 3 vertices enough to decide if coincident
                else if (((++ count) >= 3) && !onFrontSide && !onBackSide)
                {   
                        return COINCIDENT; 
                }
        }

        if (onBackSide)
        {
                return BACK_SIDE;
        }
        else if (onFrontSide)
        {
                return FRONT_SIDE;
        }
        
        return COINCIDENT; // plane and polygon are coincident
}


Vector3 Polygon3::Center() const
{
        int i;
        Vector3 sum = mVertices[0];
        for (i=1; i < mVertices.size(); i++)
                sum += mVertices[i];
        
        return sum / (float)i;
}


bool Polygon3::Valid(const float epsilon) const
{
        if (mVertices.size() < 3)
                return false;
#if 0
        // matt: removed for performance issues
        // check if area exceeds certain size
        if (GetArea() < 1e-10)
        {
                cerr << "area too small: " << GetArea() << std::endl;
                return false;
        }
                
        Vector3 vtx = mVertices.back();
        VertexArray::const_iterator it, it_end = mVertices.end();

        for (it = mVertices.begin(); it != it_end; ++it)
        {
                if (EpsilonEqualV3(vtx, *it, epsilon))
                {
                        cerr << "Double vertices:\n" << *this << endl;
                        return false;
                }
                vtx = *it;
        }
#endif
        return true;
}


// int_lineseg returns 1 if the given line segment intersects a 2D
// ray travelling in the positive X direction.  This is used in the
// Jordan curve computation for polygon intersection.
inline int int_lineseg(float px,
                                           float py,
                                           float u1,
                                           float v1,
                                           float u2,
                                           float v2)
{
        float t;
        float ydiff;

        u1 -= px; u2 -= px;       // translate line
        v1 -= py; v2 -= py;

        if ((v1 > 0 && v2 > 0) ||
                (v1 < 0 && v2 < 0) ||
                (u1 < 0 && u2 < 0))
                return 0;

        if (u1 > 0 && u2 > 0)
                return 1;

        ydiff = v2 - v1;

        if (fabs(ydiff) < Limits::Small) 
        {        
                // denominator near 0
                if (((fabs(v1) > Limits::Small) || (u1 > 0) || (u2 > 0)))
                        return 0;

                return 1;
        }

        t = -v1 / ydiff; // Compute parameter

        return (u1 + t * (u2 - u1)) > 0;
}


AxisAlignedBox3 Polygon3::GetBoundingBox() const
{
        AxisAlignedBox3 box;
        box.Initialize();

        VertexArray::const_iterator vit, vit_end = mVertices.end();

        for (vit = mVertices.begin(); vit != vit_end; ++ vit)
        {
                box.Include(*vit);
        }

        return box;
}


}