java - Generate QR codes with custom dot shapes using zxing

Question

I'm writing an application to generate QR codes with custom dot shapes. What's the best way to do this using zxing?

So far, I've dug through the source code and I see that the data bits are written in com.google.zxing.qrcode.encoder.MatrixUtil.embedDataBits(). I think I could add some code on to the end of this function which would allow me to mask the dots but I'm not sure how to do this in Java. I can't extend the class because it's declared as final. Would it be a good idea and if so how would I extend this method in that way?

The other option I've been looking at involves post-processing the image produced by QRCode but this is really complex I think as I'd have to find a way to discern the dots from the positioning squares.

Is there a better way to do what I'm looking to do? Is there another QR code library besides zxing which can do what I'm looking to do out of the box?

P.S. I want to note that this is not a duplicate of this question although the keywords are similar.

Answer 1

The following java code uses zxing to make a QR-code image with circular dots and a circular finder pattern (custom rendering style). This can be adapted to other custom render styles.

I use the Encoder class directly and bypass QRCodeWriter and MatrixToImageWriter to gain enough control to alter the rendering. To alter the finder pattern, I use the fact that the finder pattern is always 7 dots wide/tall. Otherwise I would have to create a custom version of MatrixUtil (and perhaps Encoder).

Example QR Code Image Generated:

    public static void main(String[] args) {
        try {
            generateQRCodeImage("https://www.google.com", 300, 300, "./MyQRCode.png");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private static void generateQRCodeImage(String text, int width, int height, String filePath) throws WriterException, IOException {
        final Map<EncodeHintType, Object> encodingHints = new HashMap<>();
        encodingHints.put(EncodeHintType.CHARACTER_SET, "UTF-8");
        QRCode code = Encoder.encode(text, ErrorCorrectionLevel.H, encodingHints);
        BufferedImage image = renderQRImage(code, width, height, 4);
        
        try (FileOutputStream stream = new FileOutputStream(filePath)) {
            stream.write(bufferedImageToBytes(image));
        }
    }

    private static BufferedImage renderQRImage(QRCode code, int width, int height, int quietZone) {
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
        Graphics2D graphics = image.createGraphics();

        graphics.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        graphics.setBackground(Color.white);
        graphics.clearRect(0, 0, width, height);
        graphics.setColor(Color.black);

        ByteMatrix input = code.getMatrix();
        if (input == null) {
            throw new IllegalStateException();
        }
        int inputWidth = input.getWidth();
        int inputHeight = input.getHeight();
        int qrWidth = inputWidth + (quietZone * 2);
        int qrHeight = inputHeight + (quietZone * 2);
        int outputWidth = Math.max(width, qrWidth);
        int outputHeight = Math.max(height, qrHeight);

        int multiple = Math.min(outputWidth / qrWidth, outputHeight / qrHeight);
        int leftPadding = (outputWidth - (inputWidth * multiple)) / 2;
        int topPadding = (outputHeight - (inputHeight * multiple)) / 2;
        final int FINDER_PATTERN_SIZE = 7;
        final float CIRCLE_SCALE_DOWN_FACTOR = 21f/30f;
        int circleSize = (int) (multiple * CIRCLE_SCALE_DOWN_FACTOR);

        for (int inputY = 0, outputY = topPadding; inputY < inputHeight; inputY++, outputY += multiple) {
            for (int inputX = 0, outputX = leftPadding; inputX < inputWidth; inputX++, outputX += multiple) {
                if (input.get(inputX, inputY) == 1) {
                    if (!(inputX <= FINDER_PATTERN_SIZE && inputY <= FINDER_PATTERN_SIZE ||
                          inputX >= inputWidth - FINDER_PATTERN_SIZE && inputY <= FINDER_PATTERN_SIZE ||
                          inputX <= FINDER_PATTERN_SIZE && inputY >= inputHeight - FINDER_PATTERN_SIZE)) {
                        graphics.fillOval(outputX, outputY, circleSize, circleSize);
                    }
                }
            }
        }

        int circleDiameter = multiple * FINDER_PATTERN_SIZE;
        drawFinderPatternCircleStyle(graphics, leftPadding, topPadding, circleDiameter);
        drawFinderPatternCircleStyle(graphics, leftPadding + (inputWidth - FINDER_PATTERN_SIZE) * multiple, topPadding, circleDiameter);
        drawFinderPatternCircleStyle(graphics, leftPadding, topPadding + (inputHeight - FINDER_PATTERN_SIZE) * multiple, circleDiameter);

        return image;
    }

    private static void drawFinderPatternCircleStyle(Graphics2D graphics, int x, int y, int circleDiameter) {
        final int WHITE_CIRCLE_DIAMETER = circleDiameter*5/7;
        final int WHITE_CIRCLE_OFFSET = circleDiameter/7;
        final int MIDDLE_DOT_DIAMETER = circleDiameter*3/7;
        final int MIDDLE_DOT_OFFSET = circleDiameter*2/7;

        graphics.setColor(Color.black);
        graphics.fillOval(x, y, circleDiameter, circleDiameter);
        graphics.setColor(Color.white);
        graphics.fillOval(x + WHITE_CIRCLE_OFFSET, y + WHITE_CIRCLE_OFFSET, WHITE_CIRCLE_DIAMETER, WHITE_CIRCLE_DIAMETER);
        graphics.setColor(Color.black);
        graphics.fillOval(x + MIDDLE_DOT_OFFSET, y + MIDDLE_DOT_OFFSET, MIDDLE_DOT_DIAMETER, MIDDLE_DOT_DIAMETER);
    }

Maven dependency:

    <dependency>
        <groupId>com.google.zxing</groupId>
        <artifactId>core</artifactId>
        <version>3.4.0</version>
    </dependency>