2 * Copyright 2007 Google Inc.
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.detector;
19 import com.google.zxing.MonochromeBitmapSource;
20 import com.google.zxing.ReaderException;
21 import com.google.zxing.common.BitMatrix;
24 * Implementations of this class can, given locations of finder patterns for a QR code in an
25 * image, sample the right points in the image to reconstruct the QR code, accounting for
26 * perspective distortion. It is abstracted since it is relatively expensive and should be allowed
27 * to take advantage of platform-specific optimized implementations, like Sun's Java Advanced
28 * Imaging library, but which may not be available in other environments such as J2ME, and vice
31 * The implementation used can be controlled by calling {@link #setGridSampler(GridSampler)}
32 * with an instance of a class which implements this interface.
34 * @author srowen@google.com (Sean Owen)
36 public abstract class GridSampler {
38 private static GridSampler gridSampler;
41 * Sets the implementation of {@link GridSampler} used by the library. One global
42 * instance is stored, which may sound problematic. But, the implementation provided
43 * ought to be appropriate for the entire platform, and all uses of this library
44 * in the whole lifetime of the JVM. For instance, an Android activity can swap in
45 * an implementation that takes advantage of native platform libraries.
47 * @param newGridSampler
49 public static void setGridSampler(GridSampler newGridSampler) {
50 if (newGridSampler == null) {
51 throw new IllegalArgumentException();
53 gridSampler = newGridSampler;
57 * @return the current implementation of {@link GridSampler}
59 public static GridSampler getInstance() {
60 if (gridSampler == null) {
61 gridSampler = new DefaultGridSampler();
67 * <p>Given an image, locations of a QR Code's finder patterns and bottom-right alignment pattern,
68 * and the presumed dimension in modules of the QR Code, implemntations of this method extract
69 * the QR Code from the image by sampling the points in the image which should correspond to the
70 * modules of the QR Code.</p>
72 * @param image image to sample
73 * @param topLeft top-left finder pattern location
74 * @param topRight top-right finder pattern location
75 * @param bottomLeft bottom-left finder pattern location
76 * @param alignmentPattern bottom-right alignment pattern location
77 * @param dimension dimension of QR Code
78 * @return {@link BitMatrix} representing QR Code's modules
79 * @throws ReaderException if QR Code cannot be reasonably sampled -- for example if the location
80 * of the finder patterns imply a transformation that would require sampling off the image
82 protected abstract BitMatrix sampleGrid(MonochromeBitmapSource image,
83 FinderPattern topLeft,
84 FinderPattern topRight,
85 FinderPattern bottomLeft,
86 AlignmentPattern alignmentPattern,
87 int dimension) throws ReaderException;
90 * <p>Checks a set of points that have been transformed to sample points on an image against
91 * the image's dimensions to see if the endpoints are even within the image.
92 * This method actually only checks the endpoints since the points are assumed to lie
95 * <p>This method will actually "nudge" the endpoints back onto the image if they are found to be barely
96 * (less than 1 pixel) off the image. This accounts for imperfect detection of finder patterns in an image
97 * where the QR Code runs all the way to the image border.</p>
99 * @param image image into which the points should map
100 * @param points actual points in x1,y1,...,xn,yn form
101 * @throws ReaderException if an endpoint is lies outside the image boundaries
103 protected static void checkEndpoint(MonochromeBitmapSource image, float[] points) throws ReaderException {
104 int width = image.getWidth();
105 int height = image.getHeight();
106 checkOneEndpoint(points, (int) points[0], (int) points[1], width, height);
107 checkOneEndpoint(points, (int) points[points.length - 2], (int) points[points.length - 1], width, height);
110 private static void checkOneEndpoint(float[] points, int x, int y, int width, int height) throws ReaderException {
111 if (x < -1 || x > width || y < -1 || y > height) {
112 throw new ReaderException("Transformed point out of bounds at " + x + ',' + y);
121 points[0] = width - 1;
124 points[1] = height - 1;