Function orient2d

Engine/CoonsRegularization.cpp:1192–1234

Interface to orient2d predicate optimized for pairs.

// Interface to orient2d predicate optimized for pairs.
static double
orient2d(const Point& a,
         const Point& b,
         const Point& c)
{
    double detsum, errbound;
    double orient;
    double detleft = (a.x - c.x) * (b.y - c.y);
    double detright = (a.y - c.y) * (b.x - c.x);
    double det = detleft - detright;

    if (detleft > 0.0) {
        if (detright <= 0.0) {
            return det;
        } else {
            detsum = detleft + detright;
        }
    } else if (detleft < 0.0) {
        if (detright >= 0.0) {
            return det;
        } else {
            detsum = -detleft - detright;
        }
    } else {
        return det;
    }

    double ccwerrboundA = std::numeric_limits<double>::epsilon() * 0.5;
    ccwerrboundA = (3.0 + 16.0 * ccwerrboundA) * ccwerrboundA;

    errbound = ccwerrboundA * detsum;
    if ( (det >= errbound) || (-det >= errbound) ) {
        return det;
    }

    Point pa, pb, pc;
    pa = a;
    pb = b;
    pc = c;
    orient = orient2dadapt(pa, pb, pc, detsum);

    return orient;
}

// Returns true if the point z lies in or on the bounding box
// of a,b,c, and d.