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<?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\Qrcode\Detector;
use Zxing\NotFoundException;
/**
* <p>This class attempts to find alignment patterns in a QR Code. Alignment patterns look like finder
* patterns but are smaller and appear at regular intervals throughout the image.</p>
*
* <p>At the moment this only looks for the bottom-right alignment pattern.</p>
*
* <p>This is mostly a simplified copy of {@link FinderPatternFinder}. It is copied,
* pasted and stripped down here for maximum performance but does unfortunately duplicate
* some code.</p>
*
* <p>This class is thread-safe but not reentrant. Each thread must allocate its own object.</p>
*
* @author Sean Owen
*/
final class AlignmentPatternFinder
{
private array $possibleCenters = [];
private array $crossCheckStateCount = [];
/**
* <p>Creates a finder that will look in a portion of the whole image.</p>
*
* @param \Imagick image $image to search
* @param int left $startX column from which to start searching
* @param int top $startY row from which to start searching
* @param float width $width of region to search
* @param float height $height of region to search
* @param float estimated $moduleSize module size so far
*/
public function __construct(private $image, private $startX, private $startY, private $width, private $height, private $moduleSize, private $resultPointCallback)
{
}
/**
* <p>This method attempts to find the bottom-right alignment pattern in the image. It is a bit messy since
* it's pretty performance-critical and so is written to be fast foremost.</p>
*
* @return {@link AlignmentPattern} if found
* @throws NotFoundException if not found
*/
public function find()
{
$startX = $this->startX;
$height = $this->height;
$maxJ = $startX + $this->width;
$middleI = $this->startY + ($height / 2);
// We are looking for black/white/black modules in 1:1:1 ratio;
// this tracks the number of black/white/black modules seen so far
$stateCount = [];
for ($iGen = 0; $iGen < $height; $iGen++) {
// Search from middle outwards
$i = $middleI + (($iGen & 0x01) == 0 ? ($iGen + 1) / 2 : -(($iGen + 1) / 2));
$i = (int)($i);
$stateCount[0] = 0;
$stateCount[1] = 0;
$stateCount[2] = 0;
$j = $startX;
// Burn off leading white pixels before anything else; if we start in the middle of
// a white run, it doesn't make sense to count its length, since we don't know if the
// white run continued to the left of the start point
while ($j < $maxJ && !$this->image->get($j, $i)) {
$j++;
}
$currentState = 0;
while ($j < $maxJ) {
if ($this->image->get($j, $i)) {
// Black pixel
if ($currentState == 1) { // Counting black pixels
$stateCount[$currentState]++;
} else { // Counting white pixels
if ($currentState == 2) { // A winner?
if ($this->foundPatternCross($stateCount)) { // Yes
$confirmed = $this->handlePossibleCenter($stateCount, $i, $j);
if ($confirmed != null) {
return $confirmed;
}
}
$stateCount[0] = $stateCount[2];
$stateCount[1] = 1;
$stateCount[2] = 0;
$currentState = 1;
} else {
$stateCount[++$currentState]++;
}
}
} else { // White pixel
if ($currentState == 1) { // Counting black pixels
$currentState++;
}
$stateCount[$currentState]++;
}
$j++;
}
if ($this->foundPatternCross($stateCount)) {
$confirmed = $this->handlePossibleCenter($stateCount, $i, $maxJ);
if ($confirmed != null) {
return $confirmed;
}
}
}
// Hmm, nothing we saw was observed and confirmed twice. If we had
// any guess at all, return it.
if (count($this->possibleCenters)) {
return $this->possibleCenters[0];
}
throw new NotFoundException("Bottom right alignment pattern not found");
}
/**
* @param int $stateCount count of black/white/black pixels just read
*
* @return bool iff the proportions of the counts is close enough to the 1/1/1 ratios used by alignment patterns to be considered a match
*/
private function foundPatternCross($stateCount): bool
{
$moduleSize = $this->moduleSize;
$maxVariance = $moduleSize / 2.0;
for ($i = 0; $i < 3; $i++) {
if (abs($moduleSize - $stateCount[$i]) >= $maxVariance) {
return false;
}
}
return true;
}
/**
* <p>This is called when a horizontal scan finds a possible alignment pattern. It will
* cross check with a vertical scan, and if successful, will see if this pattern had been
* found on a previous horizontal scan. If so, we consider it confirmed and conclude we have
* found the alignment pattern.</p>
*
* @param array $stateCount state module counts from horizontal scan
* @param int $i where alignment pattern may be found
* @param int $j number of possible alignment pattern in row
*
* @return {@link AlignmentPattern} if we have found the same pattern twice, or null if not
*/
private function handlePossibleCenter($stateCount, $i, $j)
{
$stateCountTotal = $stateCount[0] + $stateCount[1] + $stateCount[2];
$centerJ = self::centerFromEnd($stateCount, $j);
$centerI = $this->crossCheckVertical($i, (int)$centerJ, 2 * $stateCount[1], $stateCountTotal);
if (!is_nan($centerI)) {
$estimatedModuleSize = (float)($stateCount[0] + $stateCount[1] + $stateCount[2]) / 3.0;
foreach ($this->possibleCenters as $center) {
// Look for about the same center and module size:
if ($center->aboutEquals($estimatedModuleSize, $centerI, $centerJ)) {
return $center->combineEstimate($centerI, $centerJ, $estimatedModuleSize);
}
}
// Hadn't found this before; save it
$point = new AlignmentPattern($centerJ, $centerI, $estimatedModuleSize);
$this->possibleCenters[] = $point;
if ($this->resultPointCallback != null) {
$this->resultPointCallback->foundPossibleResultPoint($point);
}
}
return null;
}
/**
* Given a count of black/white/black pixels just seen and an end position,
* figures the location of the center of this black/white/black run.
*/
private static function centerFromEnd(array $stateCount, int $end)
{
return (float)($end - $stateCount[2]) - $stateCount[1] / 2.0;
}
/**
* <p>After a horizontal scan finds a potential alignment pattern, this method
* "cross-checks" by scanning down vertically through the center of the possible
* alignment pattern to see if the same proportion is detected.</p>
*
* @param int $startI row where an alignment pattern was detected
* @param float $centerJ center of the section that appears to cross an alignment pattern
* @param int $maxCount maximum reasonable number of modules that should be
* observed in any reading state, based on the results of the horizontal scan
*
* @return float vertical center of alignment pattern, or {@link Float#NaN} if not found
*/
private function crossCheckVertical(
int $startI,
int $centerJ,
$maxCount,
$originalStateCountTotal
) {
$image = $this->image;
$maxI = $image->getHeight();
$stateCount = $this->crossCheckStateCount;
$stateCount[0] = 0;
$stateCount[1] = 0;
$stateCount[2] = 0;
// Start counting up from center
$i = $startI;
while ($i >= 0 && $image->get($centerJ, $i) && $stateCount[1] <= $maxCount) {
$stateCount[1]++;
$i--;
}
// If already too many modules in this state or ran off the edge:
if ($i < 0 || $stateCount[1] > $maxCount) {
return NAN;
}
while ($i >= 0 && !$image->get($centerJ, $i) && $stateCount[0] <= $maxCount) {
$stateCount[0]++;
$i--;
}
if ($stateCount[0] > $maxCount) {
return NAN;
}
// Now also count down from center
$i = $startI + 1;
while ($i < $maxI && $image->get($centerJ, $i) && $stateCount[1] <= $maxCount) {
$stateCount[1]++;
$i++;
}
if ($i == $maxI || $stateCount[1] > $maxCount) {
return NAN;
}
while ($i < $maxI && !$image->get($centerJ, $i) && $stateCount[2] <= $maxCount) {
$stateCount[2]++;
$i++;
}
if ($stateCount[2] > $maxCount) {
return NAN;
}
$stateCountTotal = $stateCount[0] + $stateCount[1] + $stateCount[2];
if (5 * abs($stateCountTotal - $originalStateCountTotal) >= 2 * $originalStateCountTotal) {
return NAN;
}
return $this->foundPatternCross($stateCount) ? self::centerFromEnd($stateCount, $i) : NAN;
}
}
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