//Algorytm przygotowuje vertexy do renderowania z użyciem frustum cullingu
//Dzieli całą scenę na 4 prostopadłościany, których wysokość jest równa wysokości
//sceny, a następnie każdy prostopadłościan w ten sam sposób rekurencyjnie

class TripleVertex
{
public VertexPositionColorTexture[] v = new VertexPositionColorTexture[3];
}

TripleVertex[] tritab;
tritab = new TripleVertex[boxtab.Length/3];

private void Frustum(int offset,int length, Vector2 start,Vector2 end)
{
if(length<100)return;
int[] offsets = new int[4];
int[] lengths = new int[4];
offsets[0] = offset;
lenghts[0] = length/4;
offsets[1] = offsets[0]+lenghts[0];
lenghts[1] = length/4;
offsets[2] = offsets[1]+lenghts[1];
lengths[2] = length/4;
offsets[3] = offsets[2]+lenghts[2];
lengths[3] = length-offsets[0]-offsets[1]-offsets[2];


Vector2 center = (start + end)/2.0f;
Vector2 botmid = new Vector2(center.X,start.Y);
Vector2 midrig = new Vector2(end.X,center.Y);
Vector2 midlef = new Vector2(start.X,center.Y);
Vector2 topmid = new Vector2(center.X,end.Y);

for(int la=0;la<4;la++)
    {
    Vector2 vs;
    Vector2 ve;
    switch(la)
        {
        case 0:
            vs = center;
            ve = end;
            break;
        case 1:
            vs = midlef;
            ve = topmid;
            break;
            case 2:
            vs = start;
            ve = center;
            break;
        case 3:
            vs = botmid;
            ve = midrig;
            break;
    }
    int beginIndex = offsets[la];
    int endIndex = offsets[la]+length[la];
    int i = 0;
    for(int lb=offset;lb<offset+length;lb++)
        {
        if((lb>=offsets[la])&&(lb<offsets[la]+lengths[la]))continue;
        if(IsInside(tritab[lb],vs,ve)
        {
            Swap(lb,offsets[la]+i);
            i++;
        }
        if(i>=offsets[la]+lengths[la])break;
    }
}
Frustum(offsets[0],lengths[0],center,end);
Frustum(offsets[1],lengths[1],midlef,topmid);
Frustum(offsets[2],lengths[2],start,center);
Frustum(offsets[3],lengths[3],botmid,midrig);
}

private bool IsInside(TripleVertex tri,Vector2 start,Vector2 end)
{
//czy dany face zawiera sie w kwadracie o rogach po przekątnej start i end
}

private void Swap(int a,int b)
{
//Zamiana w tablicy boxtab elementu a z elementem b
}