Function Scan

czxing/src/main/cpp/zxing/src/datamatrix/DMDetector.cpp:679–815

};

static DetectorResult Scan(EdgeTracer& startTracer, std::array<DMRegressionLine, 4>& lines)
{
	while (startTracer.moveToNextWhiteAfterBlack()) {
		log(startTracer.p);

		PointF tl, bl, br, tr;
		auto& [lineL, lineB, lineR, lineT] = lines;

		for (auto& l : lines)
			l.reset();

#ifdef PRINT_DEBUG
		SCOPE_EXIT([&] {
			for (auto& l : lines)
				log(l.points());
		});
# define CHECK(A) if (!(A)) { printf("broke at %d\n", __LINE__); continue; }
#else
# define CHECK(A) if(!(A)) continue
#endif

		auto t = startTracer;

		// follow left leg upwards
		t.turnRight();
		t.state = 1;
		CHECK(t.traceLine(t.right(), lineL));
		CHECK(t.traceCorner(t.right(), tl));
		lineL.reverse();
		auto tlTracer = t;

		// follow left leg downwards
		t = startTracer;
		t.state = 1;
		t.setDirection(tlTracer.right());
		CHECK(t.traceLine(t.left(), lineL));
		if (!lineL.isValid())
			t.updateDirectionFromOrigin(tl);
		auto up = t.back();
		CHECK(t.traceCorner(t.left(), bl));

		// follow bottom leg right
		t.state = 2;
		CHECK(t.traceLine(t.left(), lineB));
		if (!lineB.isValid())
			t.updateDirectionFromOrigin(bl);
		auto right = t.front();
		CHECK(t.traceCorner(t.left(), br));

		auto lenL = distance(tl, bl) - 1;
		auto lenB = distance(bl, br) - 1;
		CHECK(lenL >= 8 && lenB >= 10 && lenB >= lenL / 4 && lenB <= lenL * 18);

		auto maxStepSize = static_cast<int>(lenB / 5 + 1); // datamatrix bottom dim is at least 10

		// at this point we found a plausible L-shape and are now looking for the b/w pattern at the top and right:
		// follow top row right 'half way' (4 gaps), see traceGaps break condition with 'invalid' line
		tlTracer.setDirection(right);