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Core barcode encoding/decoding library
/*
* Copyright 2007 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.zxing.qrcode.decoder;
import com.google.zxing.FormatException;
import com.google.zxing.common.BitMatrix;
/**
* @author Sean Owen
*/
final class BitMatrixParser {
private final BitMatrix bitMatrix;
private Version parsedVersion;
private FormatInformation parsedFormatInfo;
private boolean mirror;
/**
* @param bitMatrix {@link BitMatrix} to parse
* @throws FormatException if dimension is not >= 21 and 1 mod 4
*/
BitMatrixParser(BitMatrix bitMatrix) throws FormatException {
int dimension = bitMatrix.getHeight();
if (dimension < 21 || (dimension & 0x03) != 1) {
throw FormatException.getFormatInstance();
}
this.bitMatrix = bitMatrix;
}
/**
* Reads format information from one of its two locations within the QR Code.
*
* @return {@link FormatInformation} encapsulating the QR Code's format info
* @throws FormatException if both format information locations cannot be parsed as
* the valid encoding of format information
*/
FormatInformation readFormatInformation() throws FormatException {
if (parsedFormatInfo != null) {
return parsedFormatInfo;
}
// Read top-left format info bits
int formatInfoBits1 = 0;
for (int i = 0; i < 6; i++) {
formatInfoBits1 = copyBit(i, 8, formatInfoBits1);
}
// .. and skip a bit in the timing pattern ...
formatInfoBits1 = copyBit(7, 8, formatInfoBits1);
formatInfoBits1 = copyBit(8, 8, formatInfoBits1);
formatInfoBits1 = copyBit(8, 7, formatInfoBits1);
// .. and skip a bit in the timing pattern ...
for (int j = 5; j >= 0; j--) {
formatInfoBits1 = copyBit(8, j, formatInfoBits1);
}
// Read the top-right/bottom-left pattern too
int dimension = bitMatrix.getHeight();
int formatInfoBits2 = 0;
int jMin = dimension - 7;
for (int j = dimension - 1; j >= jMin; j--) {
formatInfoBits2 = copyBit(8, j, formatInfoBits2);
}
for (int i = dimension - 8; i < dimension; i++) {
formatInfoBits2 = copyBit(i, 8, formatInfoBits2);
}
parsedFormatInfo = FormatInformation.decodeFormatInformation(formatInfoBits1, formatInfoBits2);
if (parsedFormatInfo != null) {
return parsedFormatInfo;
}
throw FormatException.getFormatInstance();
}
/**
* Reads version information from one of its two locations within the QR Code.
*
* @return {@link Version} encapsulating the QR Code's version
* @throws FormatException if both version information locations cannot be parsed as
* the valid encoding of version information
*/
Version readVersion() throws FormatException {
if (parsedVersion != null) {
return parsedVersion;
}
int dimension = bitMatrix.getHeight();
int provisionalVersion = (dimension - 17) / 4;
if (provisionalVersion <= 6) {
return Version.getVersionForNumber(provisionalVersion);
}
// Read top-right version info: 3 wide by 6 tall
int versionBits = 0;
int ijMin = dimension - 11;
for (int j = 5; j >= 0; j--) {
for (int i = dimension - 9; i >= ijMin; i--) {
versionBits = copyBit(i, j, versionBits);
}
}
Version theParsedVersion = Version.decodeVersionInformation(versionBits);
if (theParsedVersion != null && theParsedVersion.getDimensionForVersion() == dimension) {
parsedVersion = theParsedVersion;
return theParsedVersion;
}
// Hmm, failed. Try bottom left: 6 wide by 3 tall
versionBits = 0;
for (int i = 5; i >= 0; i--) {
for (int j = dimension - 9; j >= ijMin; j--) {
versionBits = copyBit(i, j, versionBits);
}
}
theParsedVersion = Version.decodeVersionInformation(versionBits);
if (theParsedVersion != null && theParsedVersion.getDimensionForVersion() == dimension) {
parsedVersion = theParsedVersion;
return theParsedVersion;
}
throw FormatException.getFormatInstance();
}
private int copyBit(int i, int j, int versionBits) {
boolean bit = mirror ? bitMatrix.get(j, i) : bitMatrix.get(i, j);
return bit ? (versionBits << 1) | 0x1 : versionBits << 1;
}
/**
* Reads the bits in the {@link BitMatrix} representing the finder pattern in the
* correct order in order to reconstruct the codewords bytes contained within the
* QR Code.
*
* @return bytes encoded within the QR Code
* @throws FormatException if the exact number of bytes expected is not read
*/
byte[] readCodewords() throws FormatException {
FormatInformation formatInfo = readFormatInformation();
Version version = readVersion();
// Get the data mask for the format used in this QR Code. This will exclude
// some bits from reading as we wind through the bit matrix.
DataMask dataMask = DataMask.values()[formatInfo.getDataMask()];
int dimension = bitMatrix.getHeight();
dataMask.unmaskBitMatrix(bitMatrix, dimension);
BitMatrix functionPattern = version.buildFunctionPattern();
boolean readingUp = true;
byte[] result = new byte[version.getTotalCodewords()];
int resultOffset = 0;
int currentByte = 0;
int bitsRead = 0;
// Read columns in pairs, from right to left
for (int j = dimension - 1; j > 0; j -= 2) {
if (j == 6) {
// Skip whole column with vertical alignment pattern;
// saves time and makes the other code proceed more cleanly
j--;
}
// Read alternatingly from bottom to top then top to bottom
for (int count = 0; count < dimension; count++) {
int i = readingUp ? dimension - 1 - count : count;
for (int col = 0; col < 2; col++) {
// Ignore bits covered by the function pattern
if (!functionPattern.get(j - col, i)) {
// Read a bit
bitsRead++;
currentByte <<= 1;
if (bitMatrix.get(j - col, i)) {
currentByte |= 1;
}
// If we've made a whole byte, save it off
if (bitsRead == 8) {
result[resultOffset++] = (byte) currentByte;
bitsRead = 0;
currentByte = 0;
}
}
}
}
readingUp ^= true; // readingUp = !readingUp; // switch directions
}
if (resultOffset != version.getTotalCodewords()) {
throw FormatException.getFormatInstance();
}
return result;
}
/**
* Revert the mask removal done while reading the code words. The bit matrix should revert to its original state.
*/
void remask() {
if (parsedFormatInfo == null) {
return; // We have no format information, and have no data mask
}
DataMask dataMask = DataMask.values()[parsedFormatInfo.getDataMask()];
int dimension = bitMatrix.getHeight();
dataMask.unmaskBitMatrix(bitMatrix, dimension);
}
/**
* Prepare the parser for a mirrored operation.
* This flag has effect only on the {@link #readFormatInformation()} and the
* {@link #readVersion()}. Before proceeding with {@link #readCodewords()} the
* {@link #mirror()} method should be called.
*
* @param mirror Whether to read version and format information mirrored.
*/
void setMirror(boolean mirror) {
parsedVersion = null;
parsedFormatInfo = null;
this.mirror = mirror;
}
/** Mirror the bit matrix in order to attempt a second reading. */
void mirror() {
for (int x = 0; x < bitMatrix.getWidth(); x++) {
for (int y = x + 1; y < bitMatrix.getHeight(); y++) {
if (bitMatrix.get(x, y) != bitMatrix.get(y, x)) {
bitMatrix.flip(y, x);
bitMatrix.flip(x, y);
}
}
}
}
}