GridSampler.php

<?php
/*
* 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.
*/

namespace Zxing\Common;

use Zxing\NotFoundException;

/**
 * Implementations of this class can, given locations of finder patterns for a QR code in an
 * image, sample the right points in the image to reconstruct the QR code, accounting for
 * perspective distortion. It is abstracted since it is relatively expensive and should be allowed
 * to take advantage of platform-specific optimized implementations, like Sun's Java Advanced
 * Imaging library, but which may not be available in other environments such as J2ME, and vice
 * versa.
 *
 * The implementation used can be controlled by calling {@link #setGridSampler(GridSampler)}
 * with an instance of a class which implements this interface.
 *
 * @author Sean Owen
 */
abstract class GridSampler
{
    private static $gridSampler;

    /**
     * Sets the implementation of GridSampler used by the library. One global
     * instance is stored, which may sound problematic. But, the implementation provided
     * ought to be appropriate for the entire platform, and all uses of this library
     * in the whole lifetime of the JVM. For instance, an Android activity can swap in
     * an implementation that takes advantage of native platform libraries.
     *
     * @param newGridSampler The platform-specific object to install.
     */
    public static function setGridSampler($newGridSampler)
    {
        self::$gridSampler = $newGridSampler;
    }

    /**
     * @return the current implementation of GridSampler
     */
    public static function getInstance()
    {
        if (!self::$gridSampler) {
            self::$gridSampler = new DefaultGridSampler();
        }

        return self::$gridSampler;
    }

    /**
     * <p>Checks a set of points that have been transformed to sample points on an image against
     * the image's dimensions to see if the point are even within the image.</p>
     *
     * <p>This method will actually "nudge" the endpoints back onto the image if they are found to be
     * barely (less than 1 pixel) off the image. This accounts for imperfect detection of finder
     * patterns in an image where the QR Code runs all the way to the image border.</p>
     *
     * <p>For efficiency, the method will check points from either end of the line until one is found
     * to be within the image. Because the set of points are assumed to be linear, this is valid.</p>
     *
     * @param image  image into which the points should map
     * @param points actual points in x1,y1,...,xn,yn form
     *
     * @throws NotFoundException if an endpoint is lies outside the image boundaries
     */
    protected static function checkAndNudgePoints(
        $image,
        $points
    ) {
        $width  = $image->getWidth();
        $height = $image->getHeight();
// Check and nudge points from start until we see some that are OK:
        $nudged = true;
        for ($offset = 0; $offset < count($points) && $nudged; $offset += 2) {
            $x = (int)$points[$offset];
            $y = (int)$points[$offset + 1];
            if ($x < -1 || $x > $width || $y < -1 || $y > $height) {
                throw NotFoundException::getNotFoundInstance();
            }
            $nudged = false;
            if ($x == -1) {
                $points[$offset] = 0.0;
                $nudged          = true;
            } else if ($x == $width) {
                $points[$offset] = $width - 1;
                $nudged          = true;
            }
            if ($y == -1) {
                $points[$offset + 1] = 0.0;
                $nudged              = true;
            } else if ($y == $height) {
                $points[$offset + 1] = $height - 1;
                $nudged              = true;
            }
        }
// Check and nudge points from end:
        $nudged = true;
        for ($offset = count($points) - 2; $offset >= 0 && $nudged; $offset -= 2) {
            $x = (int)$points[$offset];
            $y = (int)$points[$offset + 1];
            if ($x < -1 || $x > $width || $y < -1 || $y > $height) {
                throw NotFoundException::getNotFoundInstance();
            }
            $nudged = false;
            if ($x == -1) {
                $points[$offset] = 0.0;
                $nudged          = true;
            } else if ($x == $width) {
                $points[$offset] = $width - 1;
                $nudged          = true;
            }
            if ($y == -1) {
                $points[$offset + 1] = 0.0;
                $nudged              = true;
            } else if ($y == $height) {
                $points[$offset + 1] = $height - 1;
                $nudged              = true;
            }
        }
    }

    /**
     * Samples an image for a rectangular matrix of bits of the given dimension. The sampling
     * transformation is determined by the coordinates of 4 points, in the original and transformed
     * image space.
     *
     * @param image      image to sample
     * @param dimensionX width of {@link BitMatrix} to sample from image
     * @param dimensionY height of {@link BitMatrix} to sample from image
     * @param p1ToX      point 1 preimage X
     * @param p1ToY      point 1 preimage Y
     * @param p2ToX      point 2 preimage X
     * @param p2ToY      point 2 preimage Y
     * @param p3ToX      point 3 preimage X
     * @param p3ToY      point 3 preimage Y
     * @param p4ToX      point 4 preimage X
     * @param p4ToY      point 4 preimage Y
     * @param p1FromX    point 1 image X
     * @param p1FromY    point 1 image Y
     * @param p2FromX    point 2 image X
     * @param p2FromY    point 2 image Y
     * @param p3FromX    point 3 image X
     * @param p3FromY    point 3 image Y
     * @param p4FromX    point 4 image X
     * @param p4FromY    point 4 image Y
     *
     * @return {@link BitMatrix} representing a grid of points sampled from the image within a region
     *   defined by the "from" parameters
     * @throws NotFoundException if image can't be sampled, for example, if the transformation defined
     *   by the given points is invalid or results in sampling outside the image boundaries
     */
    public abstract function sampleGrid(
        $image,
        $dimensionX,
        $dimensionY,
        $p1ToX, $p1ToY,
        $p2ToX, $p2ToY,
        $p3ToX, $p3ToY,
        $p4ToX, $p4ToY,
        $p1FromX, $p1FromY,
        $p2FromX, $p2FromY,
        $p3FromX, $p3FromY,
        $p4FromX, $p4FromY
    );

    public abstract function sampleGrid_(
        $image,
        $dimensionX,
        $dimensionY,
        $transform
    );

}