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<?php
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/*
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* Copyright 2007 ZXing authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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namespace Zxing\Qrcode\Detector;
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use Zxing\NotFoundException;
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use Zxing\ResultPointCallback;
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use Zxing\Common\BitMatrix;
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/**
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* <p>This class attempts to find alignment patterns in a QR Code. Alignment patterns look like finder
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* patterns but are smaller and appear at regular intervals throughout the image.</p>
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*
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* <p>At the moment this only looks for the bottom-right alignment pattern.</p>
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*
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* <p>This is mostly a simplified copy of {@link FinderPatternFinder}. It is copied,
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* pasted and stripped down here for maximum performance but does unfortunately duplicate
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* some code.</p>
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*
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* <p>This class is thread-safe but not reentrant. Each thread must allocate its own object.</p>
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*
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* @author Sean Owen
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*/
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final class AlignmentPatternFinder
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{
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private $image;
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private $possibleCenters;
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private $startX;
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private $startY;
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private $width;
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private $height;
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private $moduleSize;
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private $crossCheckStateCount;
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private $resultPointCallback;
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/**
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* <p>Creates a finder that will look in a portion of the whole image.</p>
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*
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* @param image image to search
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* @param startX left column from which to start searching
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* @param startY top row from which to start searching
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* @param width width of region to search
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* @param height height of region to search
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* @param moduleSize estimated module size so far
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*/
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public function __construct($image,
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$startX,
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$startY,
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$width,
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$height,
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$moduleSize,
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$resultPointCallback)
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{
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$this->image = $image;
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$this->possibleCenters = [];
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$this->startX = $startX;
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$this->startY = $startY;
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$this->width = $width;
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$this->height = $height;
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$this->moduleSize = $moduleSize;
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$this->crossCheckStateCount = [];
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$this->resultPointCallback = $resultPointCallback;
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}
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/**
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* <p>This method attempts to find the bottom-right alignment pattern in the image. It is a bit messy since
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* it's pretty performance-critical and so is written to be fast foremost.</p>
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*
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* @return {@link AlignmentPattern} if found
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* @throws NotFoundException if not found
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*/
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public function find()
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{
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$startX = $this->startX;
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$height = $this->height;
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$maxJ = $startX + $this->width;
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$middleI = $this->startY + ($height / 2);
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// We are looking for black/white/black modules in 1:1:1 ratio;
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// this tracks the number of black/white/black modules seen so far
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$stateCount = [];
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for ($iGen = 0; $iGen < $height; $iGen++) {
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// Search from middle outwards
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$i = $middleI + (($iGen & 0x01) == 0 ? ($iGen + 1) / 2 : -(($iGen + 1) / 2));
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$i = (int)($i);
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$stateCount[0] = 0;
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$stateCount[1] = 0;
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$stateCount[2] = 0;
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$j = $startX;
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// Burn off leading white pixels before anything else; if we start in the middle of
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// a white run, it doesn't make sense to count its length, since we don't know if the
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// white run continued to the left of the start point
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while ($j < $maxJ && !$this->image->get($j, $i)) {
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$j++;
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}
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$currentState = 0;
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while ($j < $maxJ) {
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if ($this->image->get($j, $i)) {
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// Black pixel
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if ($currentState == 1) { // Counting black pixels
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$stateCount[$currentState]++;
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} else { // Counting white pixels
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if ($currentState == 2) { // A winner?
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if ($this->foundPatternCross($stateCount)) { // Yes
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$confirmed = $this->handlePossibleCenter($stateCount, $i, $j);
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if ($confirmed != null) {
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return $confirmed;
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}
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}
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$stateCount[0] = $stateCount[2];
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$stateCount[1] = 1;
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$stateCount[2] = 0;
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$currentState = 1;
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} else {
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$stateCount[++$currentState]++;
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}
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}
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} else { // White pixel
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if ($currentState == 1) { // Counting black pixels
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$currentState++;
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}
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$stateCount[$currentState]++;
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}
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$j++;
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}
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if ($this->foundPatternCross($stateCount)) {
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$confirmed = $this->handlePossibleCenter($stateCount, $i, $maxJ);
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if ($confirmed != null) {
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return $confirmed;
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}
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}
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}
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// Hmm, nothing we saw was observed and confirmed twice. If we had
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// any guess at all, return it.
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if (count($this->possibleCenters)) {
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return $this->possibleCenters[0];
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}
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throw NotFoundException::getNotFoundInstance();
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}
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/**
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* @param stateCount count of black/white/black pixels just read
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*
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* @return true iff the proportions of the counts is close enough to the 1/1/1 ratios
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* used by alignment patterns to be considered a match
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*/
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private function foundPatternCross($stateCount)
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{
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$moduleSize = $this->moduleSize;
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$maxVariance = $moduleSize / 2.0;
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for ($i = 0; $i < 3; $i++) {
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if (abs($moduleSize - $stateCount[$i]) >= $maxVariance) {
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return false;
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}
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}
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return true;
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}
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/**
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* <p>This is called when a horizontal scan finds a possible alignment pattern. It will
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* cross check with a vertical scan, and if successful, will see if this pattern had been
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* found on a previous horizontal scan. If so, we consider it confirmed and conclude we have
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* found the alignment pattern.</p>
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*
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* @param stateCount reading state module counts from horizontal scan
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* @param i row where alignment pattern may be found
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* @param j end of possible alignment pattern in row
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*
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* @return {@link AlignmentPattern} if we have found the same pattern twice, or null if not
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*/
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private function handlePossibleCenter($stateCount, $i, $j)
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{
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$stateCountTotal = $stateCount[0] + $stateCount[1] + $stateCount[2];
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$centerJ = $this->centerFromEnd($stateCount, $j);
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$centerI = $this->crossCheckVertical($i, (int)$centerJ, 2 * $stateCount[1], $stateCountTotal);
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if (!is_nan($centerI)) {
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$estimatedModuleSize = (float)($stateCount[0] + $stateCount[1] + $stateCount[2]) / 3.0;
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foreach ($this->possibleCenters as $center) {
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// Look for about the same center and module size:
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if ($center->aboutEquals($estimatedModuleSize, $centerI, $centerJ)) {
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return $center->combineEstimate($centerI, $centerJ, $estimatedModuleSize);
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}
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}
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// Hadn't found this before; save it
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$point = new AlignmentPattern($centerJ, $centerI, $estimatedModuleSize);
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$this->possibleCenters[] = $point;
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if ($this->resultPointCallback != null) {
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$this->resultPointCallback->foundPossibleResultPoint($point);
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}
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}
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return null;
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}
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/**
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* Given a count of black/white/black pixels just seen and an end position,
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* figures the location of the center of this black/white/black run.
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*/
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private static function centerFromEnd($stateCount, $end)
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{
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return (float)($end - $stateCount[2]) - $stateCount[1] / 2.0;
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}
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/**
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* <p>After a horizontal scan finds a potential alignment pattern, this method
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* "cross-checks" by scanning down vertically through the center of the possible
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* alignment pattern to see if the same proportion is detected.</p>
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*
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* @param startI row where an alignment pattern was detected
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* @param centerJ center of the section that appears to cross an alignment pattern
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* @param maxCount maximum reasonable number of modules that should be
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* observed in any reading state, based on the results of the horizontal scan
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*
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* @return vertical center of alignment pattern, or {@link Float#NaN} if not found
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*/
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private function crossCheckVertical($startI, $centerJ, $maxCount,
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$originalStateCountTotal)
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{
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$image = $this->image;
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$maxI = $image->getHeight();
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$stateCount = $this->crossCheckStateCount;
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$stateCount[0] = 0;
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$stateCount[1] = 0;
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$stateCount[2] = 0;
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// Start counting up from center
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$i = $startI;
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while ($i >= 0 && $image->get($centerJ, $i) && $stateCount[1] <= $maxCount) {
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$stateCount[1]++;
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$i--;
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}
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// If already too many modules in this state or ran off the edge:
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if ($i < 0 || $stateCount[1] > $maxCount) {
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return NAN;
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}
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while ($i >= 0 && !$image->get($centerJ, $i) && $stateCount[0] <= $maxCount) {
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$stateCount[0]++;
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$i--;
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}
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if ($stateCount[0] > $maxCount) {
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return NAN;
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}
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// Now also count down from center
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$i = $startI + 1;
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while ($i < $maxI && $image->get($centerJ, $i) && $stateCount[1] <= $maxCount) {
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$stateCount[1]++;
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$i++;
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}
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if ($i == $maxI || $stateCount[1] > $maxCount) {
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return NAN;
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}
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while ($i < $maxI && !$image->get($centerJ, $i) && $stateCount[2] <= $maxCount) {
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$stateCount[2]++;
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$i++;
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}
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if ($stateCount[2] > $maxCount) {
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return NAN;
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}
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$stateCountTotal = $stateCount[0] + $stateCount[1] + $stateCount[2];
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if (5 * abs($stateCountTotal - $originalStateCountTotal) >= 2 * $originalStateCountTotal) {
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return NAN;
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}
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return $this->foundPatternCross($stateCount) ? $this->centerFromEnd($stateCount, $i) : NAN;
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}
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}
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