ZXing二維碼白邊控制

使用zxing生成二維碼bitmap：

            Hashtable<EncodeHintType, String> hints = new Hashtable<EncodeHintType, String>();
            hints.put(EncodeHintType.CHARACTER_SET, "utf-8");
            
            // 圖像數據轉換，使用了矩陣轉換
            BitMatrix bitMatrix = new QRCodeWriter().encode(url,
                    BarcodeFormat.QR_CODE, width, height, hints);
            int[] pixels = new int[width * height];
            // 下面這裏按照二維碼的算法，逐個生成二維碼的圖片，
            // 兩個for循環是圖片橫列掃描的結果
            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;
                    }
                }
            }
            // 生成二維碼圖片的格式，使用ARGB_8888
            Bitmap bitmap = Bitmap.createBitmap(width, height,
                    Bitmap.Config.ARGB_8888);
            bitmap.setPixels(pixels, 0, width, 0, 0, width, height);

這是最普通的二維碼生成使用方法，用這個方法生成的二維碼發現白色邊距很大，圖像是根據矩陣生成的，那我們看一下這個矩陣是怎麼生成的，點擊QRCodeWriter().encode（）進入源碼查看：

  public BitMatrix encode(String contents,
                          BarcodeFormat format,
                          int width,
                          int height,
                          Map<EncodeHintType,?> 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);

    //看這裏，這裏返回的是我們需要的矩陣
    return renderResult(code, width, height, quietZone);
  }

從這裏可以看到，最終返回的矩陣是從另一個方法返回的，繼續點擊renderResult進去查看：

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

    //這是我們傳進來的寬高
    int inputWidth = input.getWidth();
    int inputHeight = input.getHeight();

    //再看，就是這裏，最終的二維碼寬高竟然給加了2個邊距，乘以2是左右和上下2個邊距的意思
    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;
  }

從這裏看到了，最終的寬高被加了邊距，邊距quietZone是從調用處傳進來的，那我們回頭看一下encode這個方法傳進來的這個值是怎麼來的：

//這裏定義了一個默認值
 int quietZone = QUIET_ZONE_SIZE;
    if (hints != null) {
      if (hints.containsKey(EncodeHintType.ERROR_CORRECTION)) {
        errorCorrectionLevel = ErrorCorrectionLevel.valueOf(hints.get(EncodeHintType.ERROR_CORRECTION).toString());
      }

      //這裏判斷了hints是否包含margin
      if (hints.containsKey(EncodeHintType.MARGIN)) {

        //再看這裏，從hint中獲取了margin並賦值
        quietZone = Integer.parseInt(hints.get(EncodeHintType.MARGIN).toString());
      }
    }

到了這裏就可以發現，我們的白邊其實是quietZone這個玩意兒搗鬼，還記得最開始的時候我們傳進來的hints嗎，我們在裏面添加了一個編碼格式hints.put(EncodeHintType.CHARACTER_SET, "utf-8")，同樣我們可以在這裏傳進來一個margin，這樣如果encode時可以取到我們的margin，那麼就會使用我們的margin，這樣就可以隨意控制白邊的寬度了，如下：

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

經過測試，一點白邊也沒有很醜，margin爲2時最好看，如果你不想要白邊，那麼margin賦值0即可。

完畢！