Method Split

engine/Poseidon/Graphics/Rendering/Draw/ClipDraw.cpp:676–738

some operations require that inside test is performed, not pre-calculated

// some operations require that inside test is performed, not pre-calculated
void PolyVertices::Split(TLVertexTable& mesh, PolyVertices& clip, PolyVertices& rest, Vector3Par normal, Coord d)
{
    // initialize resulting polygon
    if (_n < 3)
    {
        rest._n = clip._n = 0;
        return;
    }

    // search for first vertex inside clipping half-space
    int i;
    VertexIndex* pVertex; // previous vertex
    VertexIndex* aVertex; // actual vertex

    pVertex = _vertex + _n - 1;
    bool pOut = normal * mesh.TransPosA(*pVertex) + d < 0;

    int nClipped = 0;
    int nRest = 0;

    for (i = 0; i < _n; i++)
    {
        aVertex = _vertex + i;
        bool aOut = normal * mesh.TransPosA(*aVertex) + d < 0;
        // four possible situations
        if (aOut != pOut)
        {
            // edge going in or out
            Coord t = Intersect(mesh.TransPosA(*aVertex), mesh.TransPosA(*pVertex), normal, d);
            rest._vertex[nRest++] = clip._vertex[nClipped++] = Interpolate(mesh, *aVertex, *pVertex, t);
        }
        if (!aOut)
        {
            clip._vertex[nClipped++] = *aVertex; // point in
        }
        else
        {
            rest._vertex[nRest++] = *aVertex; // point out (in rest)
        }
        pVertex = aVertex;
        pOut = aOut;
    }

    PoseidonAssert(nClipped <= MaxPoly);
    PoseidonAssert(nRest <= MaxPoly);

    if (nClipped < 3)
    {
        clip._n = 0; // polygon completely out
    }
    else
    {
        clip._n = nClipped;
    }
    if (nRest < 3)
    {
        rest._n = 0; // polygon completely out
    }