Unable to parse a QR code that was generated from ZXing itself after 110ef9e

[jabagawee]

In response to #1567, ZXing added 110ef9e. However, this has caused ZXing to fail to decode images that it itself has created. I have attached a minimal repro below. The problem may lie in FinderPatternFinder::find, as it seems to believe that two of the three finder patterns in the image only have a count of 1.

package com.google.zxing.client.j2se;

import com.google.zxing.BarcodeFormat;
import com.google.zxing.BinaryBitmap;
import com.google.zxing.MultiFormatReader;
import com.google.zxing.common.BitMatrix;
import com.google.zxing.common.HybridBinarizer;
import com.google.zxing.qrcode.QRCodeWriter;
import org.junit.Assert;
import org.junit.Test;

import java.awt.image.BufferedImage;
import java.util.UUID;

public class QrCodeRoundTripTestCase extends Assert {
  @Test
  public void testRoundTrip() throws Exception {
    String payload = UUID.randomUUID().toString();

    QRCodeWriter writer = new QRCodeWriter();
    BitMatrix matrix = writer.encode(payload, BarcodeFormat.QR_CODE, 0, 0);
    BufferedImage image = MatrixToImageWriter.toBufferedImage(matrix);

    BufferedImageLuminanceSource source = new BufferedImageLuminanceSource(image);
    BinaryBitmap bitmap = new BinaryBitmap(new HybridBinarizer(source));
    MultiFormatReader reader = new MultiFormatReader();

    assertEquals(reader.decode(bitmap).getText(), payload);
  }
}

[jabagawee]

Interestingly, it seems that the repro above consistently passes when the width and height arguments to QRCodeWriter::encode are greater than or equal to 71 and consistently fails when those arguments are set to lower than 71. I believe that the QR code that is encoded should fit in a square of side length 37.

This seems to implicate the logic around the variable iSkip in FinderPatternFinder::find for images of very small width and height.