PDF417: prevent wrong position info with right side collapsing to (0,0)

Truncated PDF417 symbols don't have a stop-guard. The top-right and
bottom-right info for those was always (0,0). This could also happen for
normal PDF417 symbols when detecting the stop-guard failed.

This patch introduces a very crude approximation of the right side of the
symbol for this case that does at least make some sense.

I consider this a fix for zxing-cpp#866. This is related to zxing-cpp#145 and zxing-cpp#340.

core/src/pdf417/PDFDecoderResultExtra.h

@@ -33,6 +33,8 @@ class DecoderResultExtra : public CustomData
 
 public:
 
+	int approxSymbolWidth = -1;
+
 	int segmentIndex() const {
 		return _segmentIndex;
 	}

core/src/pdf417/PDFReader.cpp

@@ -9,6 +9,7 @@
 #include "PDFDetector.h"
 #include "PDFScanningDecoder.h"
 #include "PDFCodewordDecoder.h"
+#include "PDFDecoderResultExtra.h"
 #include "ReaderOptions.h"
 #include "DecoderResult.h"
 #include "DetectorResult.h"
@@ -85,7 +86,13 @@ static Barcodes DoDecode(const BinaryBitmap& image, bool multiple, bool tryRotat
 			ScanningDecoder::Decode(*detectorResult.bits, points[4], points[5], points[6], points[7],
 									GetMinCodewordWidth(points), GetMaxCodewordWidth(points));
 		if (decoderResult.isValid(returnErrors)) {
-			auto point = [&](int i) { return rotate(PointI(points[i].value())); };
+			auto point = [&](int i) {
+				auto meta = dynamic_cast<DecoderResultExtra*>(decoderResult.extra().get());
+				if (points[i].hasValue() || i < 2 || !meta)
+					return rotate(PointI(points[i].value()));
+				else
+					return rotate(PointI(points[i-2].value()) + PointI(meta->approxSymbolWidth, 0));
+			};
 			res.emplace_back(std::move(decoderResult), DetectorResult{{}, {point(0), point(2), point(3), point(1)}},
 							 BarcodeFormat::PDF417);
 			if (!multiple)
@@ -306,7 +313,7 @@ Reader::decode(const BinaryBitmap& image) const
 		// This falls through and tries the non-pure code path if we have a checksum error. This approach is
 		// currently the best option to deal with 'aliased' input like e.g. 03-aliased.png
 	}
-	
+
 	return FirstOrDefault(DoDecode(image, false, _opts.tryRotate(), _opts.returnErrors()));
 }
 

core/src/pdf417/PDFScanningDecoder.cpp

@@ -13,6 +13,7 @@
 #include "PDFCodewordDecoder.h"
 #include "PDFDetectionResult.h"
 #include "PDFDecoder.h"
+#include "PDFDecoderResultExtra.h"
 #include "PDFModulusGF.h"
 #include "ZXAlgorithms.h"
 #include "ZXTestSupport.h"
@@ -127,7 +128,7 @@ static Nullable<Codeword> DetectCodeword(const BitMatrix& image, int minColumn,
 	}
 	// TODO implement check for width and correction of black and white bars
 	// use start (and maybe stop pattern) to determine if blackbars are wider than white bars. If so, adjust.
-	// should probably done only for codewords with a lot more than 17 bits. 
+	// should probably done only for codewords with a lot more than 17 bits.
 	// The following fixes 10-1.png, which has wide black bars and small white bars
 	//    for (int i = 0; i < moduleBitCount.length; i++) {
 	//      if (i % 2 == 0) {
@@ -674,7 +675,7 @@ static DecoderResult CreateDecoderResult(DetectionResult& detectionResult)
 
 // TODO don't pass in minCodewordWidth and maxCodewordWidth, pass in barcode columns for start and stop pattern
 // columns. That way width can be deducted from the pattern column.
-// This approach also allows detecting more details about the barcode, e.g. if a bar type (white or black) is wider 
+// This approach also allows detecting more details about the barcode, e.g. if a bar type (white or black) is wider
 // than it should be. This can happen if the scanner used a bad blackpoint.
 DecoderResult
 ScanningDecoder::Decode(const BitMatrix& image, const Nullable<ResultPoint>& imageTopLeft, const Nullable<ResultPoint>& imageBottomLeft,
@@ -685,7 +686,7 @@ ScanningDecoder::Decode(const BitMatrix& image, const Nullable<ResultPoint>& ima
 	if (!BoundingBox::Create(image.width(), image.height(), imageTopLeft, imageBottomLeft, imageTopRight, imageBottomRight, boundingBox)) {
 		return {};
 	}
-	
+
 	Nullable<DetectionResultColumn> leftRowIndicatorColumn, rightRowIndicatorColumn;
 	DetectionResult detectionResult;
 	for (int i = 0; i < 2; i++) {
@@ -739,7 +740,11 @@ ScanningDecoder::Decode(const BitMatrix& image, const Nullable<ResultPoint>& ima
 			}
 		}
 	}
-	return CreateDecoderResult(detectionResult);
+	auto res = CreateDecoderResult(detectionResult);
+	auto meta = dynamic_cast<DecoderResultExtra*>(res.extra().get());
+	if (meta)
+		meta->approxSymbolWidth = (detectionResult.barcodeColumnCount() + 2) * (minCodewordWidth + maxCodewordWidth) / 2;
+	return res;
 }
 
 } // Pdf417