ZXing二维码白边控制

使用zxing生成二维码bitmap：

            Hashtable hints = new Hashtable();
            hints.put(EncodeHintType.CHARACTER_SET, "utf-8");
            
            // 图像数据转换，使用了矩阵转换
            BitMatrix bitMatrix = new QRCodeWriter().encode(url,
                    BarcodeFormat.QR_CODE, width, height, hints);
            int[] pixels = new int[width * height];
            // 下面这里按照二维码的算法，逐个生成二维码的图片，
            // 两个for循环是图片横列扫描的结果
            for (int y = 0; y < height; y++) {
                for (int x = 0; x < width; x++) {
                    if (bitMatrix.get(x, y)) {
                        pixels[y * width + x] = 0xff000000;
                    } else {
                        pixels[y * width + x] = 0xffffffff;
                    }
                }
            }
            // 生成二维码图片的格式，使用ARGB_8888
            Bitmap bitmap = Bitmap.createBitmap(width, height,
                    Bitmap.Config.ARGB_8888);
            bitmap.setPixels(pixels, 0, width, 0, 0, width, height);

这是最普通的二维码生成使用方法，用这个方法生成的二维码发现白色边距很大，图像是根据矩阵生成的，那我们看一下这个矩阵是怎么生成的，点击QRCodeWriter().encode（）进入源码查看：

  public BitMatrix encode(String contents,
                          BarcodeFormat format,
                          int width,
                          int height,
                          Map hints) throws WriterException {

    if (contents.isEmpty()) {
      throw new IllegalArgumentException("Found empty contents");
    }

    if (format != BarcodeFormat.QR_CODE) {
      throw new IllegalArgumentException("Can only encode QR_CODE, but got " + format);
    }

    if (width < 0 || height < 0) {
      throw new IllegalArgumentException("Requested dimensions are too small: " + width + 'x' +
          height);
    }

    ErrorCorrectionLevel errorCorrectionLevel = ErrorCorrectionLevel.L;
    int quietZone = QUIET_ZONE_SIZE;
    if (hints != null) {
      if (hints.containsKey(EncodeHintType.ERROR_CORRECTION)) {
        errorCorrectionLevel = ErrorCorrectionLevel.valueOf(hints.get(EncodeHintType.ERROR_CORRECTION).toString());
      }
      if (hints.containsKey(EncodeHintType.MARGIN)) {
        quietZone = Integer.parseInt(hints.get(EncodeHintType.MARGIN).toString());
      }
    }

    QRCode code = Encoder.encode(contents, errorCorrectionLevel, hints);

    //看这里，这里返回的是我们需要的矩阵
    return renderResult(code, width, height, quietZone);
  }

从这里可以看到，最终返回的矩阵是从另一个方法返回的，继续点击renderResult进去查看：

  private static BitMatrix renderResult(QRCode code, int width, int height, int quietZone) {
    ByteMatrix input = code.getMatrix();
    if (input == null) {
      throw new IllegalStateException();
    }

    //这是我们传进来的宽高
    int inputWidth = input.getWidth();
    int inputHeight = input.getHeight();

    //再看，就是这里，最终的二维码宽高竟然给加了2个边距，乘以2是左右和上下2个边距的意思
    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);
    // Padding includes both the quiet zone and the extra white pixels to accommodate the requested
    // dimensions. For example, if input is 25x25 the QR will be 33x33 including the quiet zone.
    // If the requested size is 200x160, the multiple will be 4, for a QR of 132x132. These will
    // handle all the padding from 100x100 (the actual QR) up to 200x160.
    int leftPadding = (outputWidth - (inputWidth * multiple)) / 2;
    int topPadding = (outputHeight - (inputHeight * multiple)) / 2;

    BitMatrix output = new BitMatrix(outputWidth, outputHeight);

    for (int inputY = 0, outputY = topPadding; inputY < inputHeight; inputY++, outputY += multiple) {
      // Write the contents of this row of the barcode
      for (int inputX = 0, outputX = leftPadding; inputX < inputWidth; inputX++, outputX += multiple) {
        if (input.get(inputX, inputY) == 1) {
          output.setRegion(outputX, outputY, multiple, multiple);
        }
      }
    }

    return output;
  }

从这里看到了，最终的宽高被加了边距，边距quietZone是从调用处传进来的，那我们回头看一下encode这个方法传进来的这个值是怎么来的：

//这里定义了一个默认值
 int quietZone = QUIET_ZONE_SIZE;
    if (hints != null) {
      if (hints.containsKey(EncodeHintType.ERROR_CORRECTION)) {
        errorCorrectionLevel = ErrorCorrectionLevel.valueOf(hints.get(EncodeHintType.ERROR_CORRECTION).toString());
      }

      //这里判断了hints是否包含margin
      if (hints.containsKey(EncodeHintType.MARGIN)) {

        //再看这里，从hint中获取了margin并赋值
        quietZone = Integer.parseInt(hints.get(EncodeHintType.MARGIN).toString());
      }
    }

到了这里就可以发现，我们的白边其实是quietZone这个玩意儿捣鬼，还记得最开始的时候我们传进来的hints吗，我们在里面添加了一个编码格式hints.put(EncodeHintType.CHARACTER_SET, "utf-8")，同样我们可以在这里传进来一个margin，这样如果encode时可以取到我们的margin，那么就会使用我们的margin，这样就可以随意控制白边的宽度了，如下：

Hashtable hints = new Hashtable();
hints.put(EncodeHintType.CHARACTER_SET, "utf-8");
hints.put(EncodeHintType.MARGIN,"2");

经过测试，一点白边也没有很丑，margin为2时最好看，如果你不想要白边，那么margin赋值0即可。

完毕！