gistfile1.hpp

void ClipEndAgainstPlane(Vector4D& a, Vector4D& b, int axis)
{
    std::cout << "  ClipEndAgainstPane " << a << b << std::endl;
    // Positive side
    if (a[axis] > a[3])
    {
        double alpha = (a[3] - a[axis])/(b[axis] - a[axis]);
        std::cout << "   Clipping against positive " << alpha << std::endl;
        for(int i = 0; i < 4; ++i)
        {
            a[i] = a[i] + (alpha * (b[i] - a[i]));
        }
    }

    if (a[axis] < -a[3])
    {
        double alpha = (a[3] + a[axis])/(b[axis] - a[axis]);
        std::cout << "   Clipping against negative " << alpha << std::endl;
        for(int i = 0; i < 4; ++i)
        {
            a[i] = a[i] + (alpha * (b[i] - a[i]));
        }
    }
    std::cout << "   End ClipEndAgainstPane " << a << b << std::endl;
}

bool ClipLineAgainstPlane(Vector4D& a, Vector4D& b, int axis)
{
    std::cout << "ClipLineAgainstPane " << axis << a << b << std::endl;
    // If both ends are outside, don't use the line at all.
    if (a[axis] > a[3] && b[axis] > a[3]) return true;

    ClipEndAgainstPlane(a, b, axis);
    ClipEndAgainstPlane(b, a, axis);

    std::cout << "End ClipLineAgainstPane " << a << b << std::endl;

    // Line is useful
    return false;
}

bool eliminated = false;
for (int i = 0; i < 3 && !eliminated; ++i)
{
    if (ClipLineAgainstPlane(projBegin, projEnd, i)) eliminated = true;
}
if (eliminated) continue;