2 * Copyright 2007 ZXing authors
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 package com.google.zxing.qrcode.decoder;
19 import com.google.zxing.common.BitMatrix;
22 * <p>Encapsulates data masks for the data bits in a QR code, per ISO 18004:2006 6.8. Implementations
23 * of this class can un-mask a raw BitMatrix. For simplicity, they will unmask the entire BitMatrix,
24 * including areas used for finder patterns, timing patterns, etc. These areas should be unused
25 * after the point they are unmasked anyway.</p>
27 * <p>Note that the diagram in section 6.8.1 is misleading since it indicates that i is column position
28 * and j is row position. In fact, as the text says, i is row position and j is column position.</p>
32 abstract class DataMask {
35 * See ISO 18004:2006 6.8.1
37 private static final DataMask[] DATA_MASKS = {
52 * <p>Implementations of this method reverse the data masking process applied to a QR Code and
53 * make its bits ready to read.</p>
55 * @param bits representation of QR Code bits
56 * @param dimension dimension of QR Code, represented by bits, being unmasked
58 final void unmaskBitMatrix(BitMatrix bits, int dimension) {
59 for (int i = 0; i < dimension; i++) {
60 for (int j = 0; j < dimension; j++) {
68 abstract boolean isMasked(int i, int j);
71 * @param reference a value between 0 and 7 indicating one of the eight possible
72 * data mask patterns a QR Code may use
73 * @return DataMask encapsulating the data mask pattern
75 static DataMask forReference(int reference) {
76 if (reference < 0 || reference > 7) {
77 throw new IllegalArgumentException();
79 return DATA_MASKS[reference];
83 * 000: mask bits for which (x + y) mod 2 == 0
85 private static final class DataMask000 extends DataMask {
87 boolean isMasked(int i, int j) {
88 return ((i + j) & 0x01) == 0;
93 * 001: mask bits for which x mod 2 == 0
95 private static final class DataMask001 extends DataMask {
97 boolean isMasked(int i, int j) {
98 return (i & 0x01) == 0;
103 * 010: mask bits for which y mod 3 == 0
105 private static final class DataMask010 extends DataMask {
107 boolean isMasked(int i, int j) {
113 * 011: mask bits for which (x + y) mod 3 == 0
115 private static final class DataMask011 extends DataMask {
117 boolean isMasked(int i, int j) {
118 return (i + j) % 3 == 0;
123 * 100: mask bits for which (x/2 + y/3) mod 2 == 0
125 private static final class DataMask100 extends DataMask {
127 boolean isMasked(int i, int j) {
128 return (((i >>> 1) + (j /3)) & 0x01) == 0;
133 * 101: mask bits for which xy mod 2 + xy mod 3 == 0
135 private static final class DataMask101 extends DataMask {
137 boolean isMasked(int i, int j) {
139 return (temp & 0x01) + (temp % 3) == 0;
144 * 110: mask bits for which (xy mod 2 + xy mod 3) mod 2 == 0
146 private static final class DataMask110 extends DataMask {
148 boolean isMasked(int i, int j) {
150 return (((temp & 0x01) + (temp % 3)) & 0x01) == 0;
155 * 111: mask bits for which ((x+y)mod 2 + xy mod 3) mod 2 == 0
157 private static final class DataMask111 extends DataMask {
159 boolean isMasked(int i, int j) {
160 return ((((i + j) & 0x01) + ((i * j) % 3)) & 0x01) == 0;