序
本文主要研究下zxing的qrcode的一些代码。
maven
com.google.zxing
core
3.3.1
com.google.zxing
javase
3.3.1
QRCodeWriter
core-3.3.1-sources.jar!/com/google/zxing/qrcode/QRCodeWriter.java
QRCodeWriter的encode方法进行编码，转换为BitMatrix
@Override
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);
return renderResult(code, width, height, quietZone);
}
QRCode
core-3.3.1-sources.jar!/com/google/zxing/qrcode/encoder/QRCode.java
public final class QRCode {
public static final int NUM_MASK_PATTERNS = 8;
private Mode mode;
private ErrorCorrectionLevel ecLevel;
private Version version;
private int maskPattern;
private ByteMatrix matrix;
public QRCode() {
maskPattern = -1;
}
public Mode getMode() {
return mode;
}
public ErrorCorrectionLevel getECLevel() {
return ecLevel;
}
public Version getVersion() {
return version;
}
public int getMaskPattern() {
return maskPattern;
}
public ByteMatrix getMatrix() {
return matrix;
}
@Override
public String toString() {
StringBuilder result = new StringBuilder(200);
result.append("<<\n");
result.append(" mode: ");
result.append(mode);
result.append("\n ecLevel: ");
result.append(ecLevel);
result.append("\n version: ");
result.append(version);
result.append("\n maskPattern: ");
result.append(maskPattern);
if (matrix == null) {
result.append("\n matrix: null\n");
} else {
result.append("\n matrix:\n");
result.append(matrix);
}
result.append(">>\n");
return result.toString();
}
public void setMode(Mode value) {
mode = value;
}
public void setECLevel(ErrorCorrectionLevel value) {
ecLevel = value;
}
public void setVersion(Version version) {
this.version = version;
}
public void setMaskPattern(int value) {
maskPattern = value;
}
public void setMatrix(ByteMatrix value) {
matrix = value;
}
// Check if "mask_pattern" is valid.
public static boolean isValidMaskPattern(int maskPattern) {
return maskPattern >= 0 && maskPattern < NUM_MASK_PATTERNS;
}
}
是由Encoder类encode而来
Encoder
core/3.3.1/core-3.3.1-sources.jar!/com/google/zxing/qrcode/encoder/Encoder.java
public static QRCode encode(String content,
ErrorCorrectionLevel ecLevel,
Map hints) throws WriterException {
// Determine what character encoding has been specified by the caller, if any
String encoding = DEFAULT_BYTE_MODE_ENCODING;
boolean hasEncodingHint = hints != null && hints.containsKey(EncodeHintType.CHARACTER_SET);
if (hasEncodingHint) {
encoding = hints.get(EncodeHintType.CHARACTER_SET).toString();
}
// Pick an encoding mode appropriate for the content. Note that this will not attempt to use
// multiple modes / segments even if that were more efficient. Twould be nice.
Mode mode = chooseMode(content, encoding);
// This will store the header information, like mode and
// length, as well as "header" segments like an ECI segment.
BitArray headerBits = new BitArray();
// Append ECI segment if applicable
if (mode == Mode.BYTE && (hasEncodingHint || !DEFAULT_BYTE_MODE_ENCODING.equals(encoding))) {
CharacterSetECI eci = CharacterSetECI.getCharacterSetECIByName(encoding);
if (eci != null) {
appendECI(eci, headerBits);
}
}
// (With ECI in place,) Write the mode marker
appendModeInfo(mode, headerBits);
// Collect data within the main segment, separately, to count its size if needed. Don't add it to
// main payload yet.
BitArray dataBits = new BitArray();
appendBytes(content, mode, dataBits, encoding);
Version version;
if (hints != null && hints.containsKey(EncodeHintType.QR_VERSION)) {
int versionNumber = Integer.parseInt(hints.get(EncodeHintType.QR_VERSION).toString());
version = Version.getVersionForNumber(versionNumber);
int bitsNeeded = calculateBitsNeeded(mode, headerBits, dataBits, version);
if (!willFit(bitsNeeded, version, ecLevel)) {
throw new WriterException("Data too big for requested version");
}
} else {
version = recommendVersion(ecLevel, mode, headerBits, dataBits);
}
BitArray headerAndDataBits = new BitArray();
headerAndDataBits.appendBitArray(headerBits);
// Find "length" of main segment and write it
int numLetters = mode == Mode.BYTE ? dataBits.getSizeInBytes() : content.length();
appendLengthInfo(numLetters, version, mode, headerAndDataBits);
// Put data together into the overall payload
headerAndDataBits.appendBitArray(dataBits);
Version.ECBlocks ecBlocks = version.getECBlocksForLevel(ecLevel);
int numDataBytes = version.getTotalCodewords() - ecBlocks.getTotalECCodewords();
// Terminate the bits properly.
terminateBits(numDataBytes, headerAndDataBits);
// Interleave data bits with error correction code.
BitArray finalBits = interleaveWithECBytes(headerAndDataBits,
version.getTotalCodewords(),
numDataBytes,
ecBlocks.getNumBlocks());
QRCode qrCode = new QRCode();
qrCode.setECLevel(ecLevel);
qrCode.setMode(mode);
qrCode.setVersion(version);
// Choose the mask pattern and set to "qrCode".
int dimension = version.getDimensionForVersion();
ByteMatrix matrix = new ByteMatrix(dimension, dimension);
int maskPattern = chooseMaskPattern(finalBits, ecLevel, version, matrix);
qrCode.setMaskPattern(maskPattern);
// Build the matrix and set it to "qrCode".
MatrixUtil.buildMatrix(finalBits, ecLevel, version, maskPattern, matrix);
qrCode.setMatrix(matrix);
return qrCode;
}
这里重点看Version的这段
Version version;
if (hints != null && hints.containsKey(EncodeHintType.QR_VERSION)) {
int versionNumber = Integer.parseInt(hints.get(EncodeHintType.QR_VERSION).toString());
version = Version.getVersionForNumber(versionNumber);
int bitsNeeded = calculateBitsNeeded(mode, headerBits, dataBits, version);
if (!willFit(bitsNeeded, version, ecLevel)) {
throw new WriterException("Data too big for requested version");
}
} else {
version = recommendVersion(ecLevel, mode, headerBits, dataBits);
}
这里计算version，同时判断content的大小，是否超出qrcode的容量，超出的话，抛出WriterException("Data too big for requested version")
- willFit计算方法
/**
* @return true if the number of input bits will fit in a code with the specified version and
* error correction level.
*/
private static boolean willFit(int numInputBits, Version version, ErrorCorrectionLevel ecLevel) {
// In the following comments, we use numbers of Version 7-H.
// numBytes = 196
int numBytes = version.getTotalCodewords();
// getNumECBytes = 130
Version.ECBlocks ecBlocks = version.getECBlocksForLevel(ecLevel);
int numEcBytes = ecBlocks.getTotalECCodewords();
// getNumDataBytes = 196 - 130 = 66
int numDataBytes = numBytes - numEcBytes;
int totalInputBytes = (numInputBits + 7) / 8;
return numDataBytes >= totalInputBytes;
}
QRCodeWriter.renderResult
// Note that the input matrix uses 0 == white, 1 == black, while the output matrix uses
// 0 == black, 255 == white (i.e. an 8 bit greyscale bitmap).
private static BitMatrix renderResult(QRCode code, int width, int height, int quietZone) {
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);
// 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;
}
这个renderResult根据QRCode信息来构造BitMatrix。可以看到这里重新计算了输出的宽度和高度，是取了qrcode的宽高+两边的quietZone与输入参数的目标宽高取最大值。也就是说如果qrcode的宽高大于目标的宽高，则以qrcode的宽高为准，这种情况下的quietZone基本跟输出的一致。
一般而言qrcode的宽高小于目标宽高的话，这种情况下quietZone就跟输出的不一致，需要经过重新放大，得到的才是最后输出的padding。
doc
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