二维码是什么？二维码有什么用？二维码绘制过程？二维码如何生成?

dependencies {  
    implementation 'com.google.zxing:core:3.5.3'  
}

QRCodeWriter qrCodeWriter = new QRCodeWriter();

int width = 350; // 二维码宽度
int height = 350; // 二维码高度
ErrorCorrectionLevel errorCorrectionLevel = ErrorCorrectionLevel.M; // 纠错级别
HashMap<EncodeHintType, ErrorCorrectionLevel> hints = new HashMap<>();
hints.put(EncodeHintType.ERROR_CORRECTION, errorCorrectionLevel);

String text = "沐雨花飞蝶";
BitMatrix bitMatrix = qrCodeWriter.encode(text, BarcodeFormat.QR_CODE, width, height, hints);

BarcodeEncoder barcodeEncoder = new BarcodeEncoder();  
Bitmap bitmap = barcodeEncoder.createBitmap(bitMatrix);

dependencies {  
    // AndroidX 版本
    implementation 'com.github.jenly1314:zxing-lite:3.1.1'
}

private fun generateQRcode(content: String, ratio: Float): Bitmap {
    val icon = BitmapFactory.decodeResource(resources, R.drawable.ic_default_profile)
    val qrCode: Bitmap = CodeUtils.createQRCode(content, 600, icon, ratio)
    return qrCode
}

/**
  * 生成二维码
  * @param content 二维码的内容
  * @param heightPix 二维码的高
  * @param logo 二维码中间的logo
  * @param ratio  logo所占比例 因为二维码的最大容错率为30%，所以建议ratio的范围小于0.3
  * @return
*/
public static Bitmap createQRCode(String content, int heightPix, Bitmap logo,@FloatRange(from = 0.0f,to = 1.0f)float ratio) {
    //配置参数
    Map<EncodeHintType, Object> hints = new HashMap<>();
    hints.put( EncodeHintType.CHARACTER_SET, "utf-8");
    //容错级别
    hints.put(EncodeHintType.ERROR_CORRECTION, ErrorCorrectionLevel.H);
    //设置空白边距的宽度
    hints.put(EncodeHintType.MARGIN, 1); //default is 4
    return createQRCode(content,heightPix,logo,ratio,hints);
}

public static Bitmap createQRCode(String content, int heightPix, Bitmap logo,@FloatRange(from = 0.0f,to = 1.0f)float ratio,Map<EncodeHintType,?> hints,int codeColor) {
    try {

        // 图像数据转换，使用了矩阵转换
        BitMatrix bitMatrix = new QRCodeWriter().encode(content, BarcodeFormat.QR_CODE, heightPix, heightPix, hints);
        int[] pixels = new int[heightPix * heightPix];
        // 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 < heightPix; y++) {
            for (int x = 0; x < heightPix; x++) {
                if (bitMatrix.get(x, y)) {
                    pixels[y * heightPix + x] = codeColor;
                } else {
                    pixels[y * heightPix + x] = Color.WHITE;
                }
            }
        }

        // 生成二维码图片的格式
        Bitmap bitmap = Bitmap.createBitmap(heightPix, heightPix, Bitmap.Config.ARGB_8888);
        bitmap.setPixels(pixels, 0, heightPix, 0, 0, heightPix, heightPix);

        if (logo != null) {
            bitmap = addLogo(bitmap, logo,ratio);
        }

        return bitmap;
    } catch (WriterException e) {
        Log.w(CaptureHelper.TAG,e.getMessage());
    }
    return null;
}

BitMatrix bitMatrix = new QRCodeWriter().encode(content, BarcodeFormat.QR_CODE, heightPix, heightPix, hints);

@Override
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);
    return renderResult(code, width, height, quietZone);
}

public enum EncodeHintType {

  /**
   * Specifies what degree of error correction to use, for example in QR Codes.
   * Type depends on the encoder. For example for QR codes it's type
   * {@link com.google.zxing.qrcode.decoder.ErrorCorrectionLevel ErrorCorrectionLevel}.
   * For Aztec it is of type {@link Integer}, representing the minimal percentage of error correction words.
   * For PDF417 it is of type {@link Integer}, valid values being 0 to 8.
   * In all cases, it can also be a {@link String} representation of the desired value as well.
   * Note: an Aztec symbol should have a minimum of 25% EC words.
   */
  ERROR_CORRECTION,

  /**
   * Specifies what character encoding to use where applicable (type {@link String})
   */
  CHARACTER_SET,

  /**
   * Specifies the matrix shape for Data Matrix (type {@link com.google.zxing.datamatrix.encoder.SymbolShapeHint})
   */
  DATA_MATRIX_SHAPE,

  /**
   * Specifies a minimum barcode size (type {@link Dimension}). Only applicable to Data Matrix now.
   *
   * @deprecated use width/height params in
   * {@link com.google.zxing.datamatrix.DataMatrixWriter#encode(String, BarcodeFormat, int, int)}
   */
  @Deprecated
  MIN_SIZE,

  /**
   * Specifies a maximum barcode size (type {@link Dimension}). Only applicable to Data Matrix now.
   *
   * @deprecated without replacement
   */
  @Deprecated
  MAX_SIZE,

  /**
   * Specifies margin, in pixels, to use when generating the barcode. The meaning can vary
   * by format; for example it controls margin before and after the barcode horizontally for
   * most 1D formats. (Type {@link Integer}, or {@link String} representation of the integer value).
   */
  MARGIN,

  /**
   * Specifies whether to use compact mode for PDF417 (type {@link Boolean}, or "true" or "false"
   * {@link String} value).
   */
  PDF417_COMPACT,

  /**
   * Specifies what compaction mode to use for PDF417 (type
   * {@link com.google.zxing.pdf417.encoder.Compaction Compaction} or {@link String} value of one of its
   * enum values).
   */
  PDF417_COMPACTION,

  /**
   * Specifies the minimum and maximum number of rows and columns for PDF417 (type
   * {@link com.google.zxing.pdf417.encoder.Dimensions Dimensions}).
   */
  PDF417_DIMENSIONS,

  /**
   * Specifies the required number of layers for an Aztec code.
   * A negative number (-1, -2, -3, -4) specifies a compact Aztec code.
   * 0 indicates to use the minimum number of layers (the default).
   * A positive number (1, 2, .. 32) specifies a normal (non-compact) Aztec code.
   * (Type {@link Integer}, or {@link String} representation of the integer value).
   */
   AZTEC_LAYERS,

   /**
    * Specifies the exact version of QR code to be encoded.
    * (Type {@link Integer}, or {@link String} representation of the integer value).
    */
   QR_VERSION,

  /**
   * Specifies whether the data should be encoded to the GS1 standard (type {@link Boolean}, or "true" or "false"
   * {@link String } value).
   */
  GS1_FORMAT,
}