enum { X, Y, Z, W };

    typedef float vec4_t[4];

    typedef float vec2_t[2];

    #define MAX_VERTICES_PRE_POLYGON  10 

    typedef struct polygon_t
    {
        //Homogenous space vertices
        unsigned char	hs_numVertices;
        vec4_t	hs_vertices[MAX_VERTICES_PRE_POLYGON];
	
    } polygon_t;




    #define vector4Subtract( a, b, c )   ((c)[ 0 ] = (a)[ 0 ] - (b)[ 0 ], \
                                          (c)[ 1 ] = (a)[ 1 ] - (b)[ 1 ], \
                                          (c)[ 2 ] = (a)[ 2 ] - (b)[ 2 ], \
                                          (c)[ 3 ] = (a)[ 3 ] - (b)[ 3 ] )

    #define vector4Add( a, b, c )        ((c)[ 0 ] = (a)[ 0 ] + (b)[ 0 ],\
                                          (c)[ 1 ] = (a)[ 1 ] + (b)[ 1 ],\
                                          (c)[ 2 ] = (a)[ 2 ] + (b)[ 2 ],\
                                          (c)[ 3 ] = (a)[ 3 ] + (b)[ 3 ] )

    #define vector4Copy( a, b )          ((b)[ 0 ] = (a)[ 0 ],\
                                          (b)[ 1 ] = (a)[ 1 ],\
                                          (b)[ 2 ] = (a)[ 2 ],\
                                          (b)[ 3 ] = (a)[ 3 ] )

    #define	vector4Scale( v, s, o )      ((o)[ 0 ] = (v)[ 0 ] * (s),\
                                          (o)[ 1 ] = (v)[ 1 ] * (s),\
                                          (o)[ 2 ] = (v)[ 2 ] * (s),\
                                          (o)[ 3 ] = (v)[ 3 ] * (s) )


    void copyVertices(vec4_t* from, polygon_t* to, int numVertices)
    {
        int i;

        to->hs_numVertices = numVertices;
        for(i=0 ; i < numVertices ; i++)
        {
            vector4Copy(from[i],to->hs_vertices[i]);
        }
    }


    #define W_CLIPPING_PLANE 0.00001 

    //Clip against plane w=W_CLIPPING_PLANE

    void ClipPolygonOnWAxis(polygon_t* face)
    {
        int i;
	
        vec4_t* currentVertice;
        vec4_t* previousVertice;
	
	
        unsigned char in_numVertices=0;
        vec4_t in_vertices[MAX_VERTICES_PRE_POLYGON];
	
        char previousDot;
        char currentDot;
	
        float intersectionFactor;
        vec4_t intersectionPoint;

	
        previousVertice = &face->hs_vertices[face->hs_numVertices-1];
        previousDot = ((*previousVertice)[W] < W_CLIPPING_PLANE) ? -1 : 1;
        currentVertice = &face->hs_vertices[0];
        while (currentVertice != &face->hs_vertices[face->hs_numVertices] ) 
        {
            currentDot = ((*currentVertice)[W] < W_CLIPPING_PLANE) ? -1 : 1;
		
        if (previousDot * currentDot < 0)
        {
            //Need to clip against plan w=0
			
            intersectionFactor = (W_CLIPPING_PLANE - (*previousVertice)[W] ) / ((*previousVertice)[W]- (*currentVertice)[W]);
			
            // I = Qp + f(Qc-Qp))
            vector4Copy(*currentVertice,intersectionPoint);                              //          Qc
            vector4Subtract(intersectionPoint, *previousVertice  ,intersectionPoint);    //         (Qc-Qp)
            vector4Scale(intersectionPoint,intersectionFactor,intersectionPoint);        //        f(Qc-Qp))
            vector4Add(intersectionPoint,*previousVertice,intersectionPoint);            //Qp    + f(Qc-Qp))
			
            // Insert
            vector4Copy(intersectionPoint,in_vertices[in_numVertices]);
            in_numVertices++;
        }
		
        if (currentDot > 0)
        {
            //Insert
            vector4Copy(*currentVertice,in_vertices[in_numVertices]);
            in_numVertices++;
        }
		
        previousDot = currentDot;
		
        //Move forward
        previousVertice = currentVertice;
        currentVertice++;
    }

    //Copy the output(in_vertices) into the source (face)
    copyVertices(in_vertices,face,in_numVertices);
    in_numVertices = 0;
}


    void ClipPolygonForAxis(polygon_t* face, int AXIS)
    {
        int i;
	
        vec4_t* currentVertice;
        vec4_t* previousVertice;
	
	
        unsigned char in_numVertices=0;
        vec4_t in_vertices[MAX_VERTICES_PRE_POLYGON];
	
        char previousDot;
        char currentDot;
	
        float intersectionFactor;
        vec4_t intersectionPoint;

        //Clip against first plane
        previousVertice = &face->hs_vertices[face->hs_numVertices-1];
        previousDot = ((*previousVertice)[AXIS] <= (*previousVertice)[W]) ? 1 : -1;
        currentVertice = &face->hs_vertices[0];
        while (currentVertice != &face->hs_vertices[face->hs_numVertices] ) 
        {
            currentDot = ((*currentVertice)[AXIS] <= (*currentVertice)[W]) ? 1 : -1;
		
            if (previousDot * currentDot < 0)
            {
                //Need to clip against plan w=0
			
                intersectionFactor = 
                ((*previousVertice)[W] - (*previousVertice)[AXIS]) / 
                (((*previousVertice)[W] - (*previousVertice)[AXIS]) - ((*currentVertice)[W] - (*currentVertice)[AXIS]) );
			
                vector4Copy(*currentVertice,intersectionPoint);
                vector4Subtract(intersectionPoint, *previousVertice  ,intersectionPoint);
                vector4Scale(intersectionPoint,intersectionFactor,intersectionPoint);
                vector4Add(intersectionPoint,*previousVertice,intersectionPoint);
			
                // Insert
                vector4Copy(intersectionPoint,in_vertices[in_numVertices]);
                in_numVertices++;
            }
		
            if (currentDot > 0)
            {
                //Insert
                vector4Copy(*currentVertice,in_vertices[in_numVertices]);
                in_numVertices++;
            }
		
            previousDot = currentDot;
		
            //Move forward
            previousVertice = currentVertice;
            currentVertice++;
        }

        //Copy the output(in_vertices) into the source (face)
        copyVertices(in_vertices,face,in_numVertices);
        in_numVertices = 0;
	
        //Clip against opposite plane
        previousVertice = &face->hs_vertices[face->hs_numVertices-1];
        previousDot = (-(*previousVertice)[AXIS] <= (*previousVertice)[W]) ? 1 : -1;
        currentVertice = &face->hs_vertices[0];
        while (currentVertice != &face->hs_vertices[face->hs_numVertices] ) 
        {
            currentDot = (-(*currentVertice)[AXIS] <= (*currentVertice)[W]) ? 1 : -1;
		
            if (previousDot * currentDot < 0)
            {
                //Need to clip against plan w=0
			
                intersectionFactor = 
                ( (*previousVertice)[W] + (*previousVertice)[AXIS]) / 
                ( ( (*previousVertice)[W] + (*previousVertice)[AXIS]) - ((*currentVertice)[W] + (*currentVertice)[AXIS]) );
			
                vector4Copy(*currentVertice,intersectionPoint);
                vector4Subtract(intersectionPoint, *previousVertice  ,intersectionPoint);
                vector4Scale(intersectionPoint,intersectionFactor,intersectionPoint);
                vector4Add(intersectionPoint,*previousVertice,intersectionPoint);
			
                // Insert
                vector4Copy(intersectionPoint,in_vertices[in_numVertices]);
                in_numVertices++;
            }
		
            if (currentDot > 0)
            {
			//Insert
			vector4Copy(*currentVertice,in_vertices[in_numVertices]);
			in_numVertices++;
            }
		
            previousDot = currentDot;
		
            //Move forward
            previousVertice = currentVertice;
            currentVertice++;
        }
        
        //Copy the output(in_vertices) into the source (face)
        copyVertices(in_vertices,face,in_numVertices);
        in_numVertices = 0;
    }

    void ClipPolygon(polygon_t* face)
    {
        ClipPolygonOnWAxis(face);       // w=W_CLIPPING_PLANE
        ClipPolygonForAxis(face,X);     // w=x   ,  w=-x
        ClipPolygonForAxis(face,Y);     // w=y   ,  w=-y
        ClipPolygonForAxis(face,Z);     // w=z   ,  w=-z
    }