Function CenterOfRing

czxing/src/main/cpp/zxing/src/ConcentricFinder.cpp:40–78

}

std::optional<PointF> CenterOfRing(const BitMatrix& image, PointI center, int range, int nth, bool requireCircle)
{
	// range is the approximate width/height of the nth ring, if nth>1 then it would be plausible to limit the search radius
	// to approximately range / 2 * sqrt(2) == range * 0.75 but it turned out to be too limiting with realworld/noisy data.
	int radius = range;
	bool inner = nth < 0;
	nth = std::abs(nth);
	log(center, 3);
	BitMatrixCursorI cur(image, center, {0, 1});
	if (!cur.stepToEdge(nth, radius, inner))
		return {};
	cur.turnRight(); // move clock wise and keep edge on the right/left depending on backup
	const auto edgeDir = inner ? Direction::LEFT : Direction::RIGHT;

	uint32_t neighbourMask = 0;
	auto start = cur.p;
	PointF sum = {};
	int n = 0;
	do {
		log(cur.p, 4);
		sum += centered(cur.p);
		++n;

		// find out if we come full circle around the center. 8 bits have to be set in the end.
		neighbourMask |= (1 << (4 + dot(bresenhamDirection(cur.p - center), PointI(1, 3))));

		if (!cur.stepAlongEdge(edgeDir))
			return {};

		// use L-inf norm, simply because it is a lot faster than L2-norm and sufficiently accurate
		if (maxAbsComponent(cur.p - center) > radius || center == cur.p || n > 4 * 2 * range)
			return {};
	} while (cur.p != start);

	if (requireCircle && neighbourMask != 0b111101111)
		return {};

	return sum / n;
}

std::optional<PointF> CenterOfRings(const BitMatrix& image, PointF center, int range, int numOfRings)
{