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+<?php
+/**
+ * Class Detector
+ *
+ * @created 17.01.2021
+ * @author ZXing Authors
+ * @author Smiley <smiley@chillerlan.net>
+ * @copyright 2021 Smiley
+ * @license Apache-2.0
+ */
+
+namespace chillerlan\QRCode\Detector;
+
+use chillerlan\QRCode\Common\{LuminanceSourceInterface, Version};
+use chillerlan\QRCode\Decoder\{Binarizer, BitMatrix};
+use function abs, intdiv, is_nan, max, min, round;
+use const NAN;
+
+/**
+ * Encapsulates logic that can detect a QR Code in an image, even if the QR Code
+ * is rotated or skewed, or partially obscured.
+ *
+ * @author Sean Owen
+ */
+final class Detector{
+
+ private BitMatrix $matrix;
+
+ /**
+ * Detector constructor.
+ */
+ public function __construct(LuminanceSourceInterface $source){
+ $this->matrix = (new Binarizer($source))->getBlackMatrix();
+ }
+
+ /**
+ * Detects a QR Code in an image.
+ */
+ public function detect():BitMatrix{
+ [$bottomLeft, $topLeft, $topRight] = (new FinderPatternFinder($this->matrix))->find();
+
+ $moduleSize = $this->calculateModuleSize($topLeft, $topRight, $bottomLeft);
+ $dimension = $this->computeDimension($topLeft, $topRight, $bottomLeft, $moduleSize);
+ $provisionalVersion = new Version(intdiv(($dimension - 17), 4));
+ $alignmentPattern = null;
+
+ // Anything above version 1 has an alignment pattern
+ if(!empty($provisionalVersion->getAlignmentPattern())){
+ // Guess where a "bottom right" finder pattern would have been
+ $bottomRightX = ($topRight->getX() - $topLeft->getX() + $bottomLeft->getX());
+ $bottomRightY = ($topRight->getY() - $topLeft->getY() + $bottomLeft->getY());
+
+ // Estimate that alignment pattern is closer by 3 modules
+ // from "bottom right" to known top left location
+ $correctionToTopLeft = (1.0 - 3.0 / (float)($provisionalVersion->getDimension() - 7));
+ $estAlignmentX = (int)($topLeft->getX() + $correctionToTopLeft * ($bottomRightX - $topLeft->getX()));
+ $estAlignmentY = (int)($topLeft->getY() + $correctionToTopLeft * ($bottomRightY - $topLeft->getY()));
+
+ // Kind of arbitrary -- expand search radius before giving up
+ for($i = 4; $i <= 16; $i <<= 1){//??????????
+ $alignmentPattern = $this->findAlignmentInRegion($moduleSize, $estAlignmentX, $estAlignmentY, (float)$i);
+
+ if($alignmentPattern !== null){
+ break;
+ }
+ }
+ // If we didn't find alignment pattern... well try anyway without it
+ }
+
+ $transform = $this->createTransform($topLeft, $topRight, $bottomLeft, $dimension, $alignmentPattern);
+
+ return (new GridSampler)->sampleGrid($this->matrix, $dimension, $transform);
+ }
+
+ /**
+ * Computes an average estimated module size based on estimated derived from the positions
+ * of the three finder patterns.
+ *
+ * @throws \chillerlan\QRCode\Detector\QRCodeDetectorException
+ */
+ private function calculateModuleSize(FinderPattern $topLeft, FinderPattern $topRight, FinderPattern $bottomLeft):float{
+ // Take the average
+ $moduleSize = ((
+ $this->calculateModuleSizeOneWay($topLeft, $topRight) +
+ $this->calculateModuleSizeOneWay($topLeft, $bottomLeft)
+ ) / 2.0);
+
+ if($moduleSize < 1.0){
+ throw new QRCodeDetectorException('module size < 1.0');
+ }
+
+ return $moduleSize;
+ }
+
+ /**
+ * Estimates module size based on two finder patterns -- it uses
+ * #sizeOfBlackWhiteBlackRunBothWays(int, int, int, int) to figure the
+ * width of each, measuring along the axis between their centers.
+ */
+ private function calculateModuleSizeOneWay(FinderPattern $a, FinderPattern $b):float{
+
+ $moduleSizeEst1 = $this->sizeOfBlackWhiteBlackRunBothWays($a->getX(), $a->getY(), $b->getX(), $b->getY());
+ $moduleSizeEst2 = $this->sizeOfBlackWhiteBlackRunBothWays($b->getX(), $b->getY(), $a->getX(), $a->getY());
+
+ if(is_nan($moduleSizeEst1)){
+ return ($moduleSizeEst2 / 7.0);
+ }
+
+ if(is_nan($moduleSizeEst2)){
+ return ($moduleSizeEst1 / 7.0);
+ }
+ // Average them, and divide by 7 since we've counted the width of 3 black modules,
+ // and 1 white and 1 black module on either side. Ergo, divide sum by 14.
+ return (($moduleSizeEst1 + $moduleSizeEst2) / 14.0);
+ }
+
+ /**
+ * See #sizeOfBlackWhiteBlackRun(int, int, int, int); computes the total width of
+ * a finder pattern by looking for a black-white-black run from the center in the direction
+ * of another po$(another finder pattern center), and in the opposite direction too.
+ *
+ * @noinspection DuplicatedCode
+ */
+ private function sizeOfBlackWhiteBlackRunBothWays(float $fromX, float $fromY, float $toX, float $toY):float{
+ $result = $this->sizeOfBlackWhiteBlackRun((int)$fromX, (int)$fromY, (int)$toX, (int)$toY);
+ $dimension = $this->matrix->getSize();
+ // Now count other way -- don't run off image though of course
+ $scale = 1.0;
+ $otherToX = ($fromX - ($toX - $fromX));
+
+ if($otherToX < 0){
+ $scale = ($fromX / ($fromX - $otherToX));
+ $otherToX = 0;
+ }
+ elseif($otherToX >= $dimension){
+ $scale = (($dimension - 1 - $fromX) / ($otherToX - $fromX));
+ $otherToX = ($dimension - 1);
+ }
+
+ $otherToY = (int)($fromY - ($toY - $fromY) * $scale);
+ $scale = 1.0;
+
+ if($otherToY < 0){
+ $scale = ($fromY / ($fromY - $otherToY));
+ $otherToY = 0;
+ }
+ elseif($otherToY >= $dimension){
+ $scale = (($dimension - 1 - $fromY) / ($otherToY - $fromY));
+ $otherToY = ($dimension - 1);
+ }
+
+ $otherToX = (int)($fromX + ($otherToX - $fromX) * $scale);
+ $result += $this->sizeOfBlackWhiteBlackRun((int)$fromX, (int)$fromY, $otherToX, $otherToY);
+
+ // Middle pixel is double-counted this way; subtract 1
+ return ($result - 1.0);
+ }
+
+ /**
+ * This method traces a line from a po$in the image, in the direction towards another point.
+ * It begins in a black region, and keeps going until it finds white, then black, then white again.
+ * It reports the distance from the start to this point.
+ *
+ * This is used when figuring out how wide a finder pattern is, when the finder pattern
+ * may be skewed or rotated.
+ */
+ private function sizeOfBlackWhiteBlackRun(int $fromX, int $fromY, int $toX, int $toY):float{
+ // Mild variant of Bresenham's algorithm;
+ // @see https://en.wikipedia.org/wiki/Bresenham%27s_line_algorithm
+ $steep = abs($toY - $fromY) > abs($toX - $fromX);
+
+ if($steep){
+ $temp = $fromX;
+ $fromX = $fromY;
+ $fromY = $temp;
+ $temp = $toX;
+ $toX = $toY;
+ $toY = $temp;
+ }
+
+ $dx = abs($toX - $fromX);
+ $dy = abs($toY - $fromY);
+ $error = (-$dx / 2);
+ $xstep = (($fromX < $toX) ? 1 : -1);
+ $ystep = (($fromY < $toY) ? 1 : -1);
+
+ // In black pixels, looking for white, first or second time.
+ $state = 0;
+ // Loop up until x == toX, but not beyond
+ $xLimit = ($toX + $xstep);
+
+ for($x = $fromX, $y = $fromY; $x !== $xLimit; $x += $xstep){
+ $realX = ($steep) ? $y : $x;
+ $realY = ($steep) ? $x : $y;
+
+ // Does current pixel mean we have moved white to black or vice versa?
+ // Scanning black in state 0,2 and white in state 1, so if we find the wrong
+ // color, advance to next state or end if we are in state 2 already
+ if(($state === 1) === $this->matrix->check($realX, $realY)){
+
+ if($state === 2){
+ return FinderPattern::distance($x, $y, $fromX, $fromY);
+ }
+
+ $state++;
+ }
+
+ $error += $dy;
+
+ if($error > 0){
+
+ if($y === $toY){
+ break;
+ }
+
+ $y += $ystep;
+ $error -= $dx;
+ }
+ }
+
+ // Found black-white-black; give the benefit of the doubt that the next pixel outside the image
+ // is "white" so this last po$at (toX+xStep,toY) is the right ending. This is really a
+ // small approximation; (toX+xStep,toY+yStep) might be really correct. Ignore this.
+ if($state === 2){
+ return FinderPattern::distance(($toX + $xstep), $toY, $fromX, $fromY);
+ }
+
+ // else we didn't find even black-white-black; no estimate is really possible
+ return NAN;
+ }
+
+ /**
+ * Computes the dimension (number of modules on a size) of the QR Code based on the position
+ * of the finder patterns and estimated module size.
+ *
+ * @throws \chillerlan\QRCode\Detector\QRCodeDetectorException
+ */
+ private function computeDimension(FinderPattern $nw, FinderPattern $ne, FinderPattern $sw, float $size):int{
+ $tltrCentersDimension = (int)round($nw->getDistance($ne) / $size);
+ $tlblCentersDimension = (int)round($nw->getDistance($sw) / $size);
+ $dimension = (int)((($tltrCentersDimension + $tlblCentersDimension) / 2) + 7);
+
+ switch($dimension % 4){
+ case 0:
+ $dimension++;
+ break;
+ // 1? do nothing
+ case 2:
+ $dimension--;
+ break;
+ case 3:
+ throw new QRCodeDetectorException('estimated dimension: '.$dimension);
+ }
+
+ if(($dimension % 4) !== 1){
+ throw new QRCodeDetectorException('dimension mod 4 is not 1');
+ }
+
+ return $dimension;
+ }
+
+ /**
+ * Attempts to locate an alignment pattern in a limited region of the image, which is
+ * guessed to contain it.
+ *
+ * @param float $overallEstModuleSize estimated module size so far
+ * @param int $estAlignmentX x coordinate of center of area probably containing alignment pattern
+ * @param int $estAlignmentY y coordinate of above
+ * @param float $allowanceFactor number of pixels in all directions to search from the center
+ *
+ * @return \chillerlan\QRCode\Detector\AlignmentPattern|null if found, or null otherwise
+ */
+ private function findAlignmentInRegion(
+ float $overallEstModuleSize,
+ int $estAlignmentX,
+ int $estAlignmentY,
+ float $allowanceFactor
+ ):?AlignmentPattern{
+ // Look for an alignment pattern (3 modules in size) around where it should be
+ $dimension = $this->matrix->getSize();
+ $allowance = (int)($allowanceFactor * $overallEstModuleSize);
+ $alignmentAreaLeftX = max(0, ($estAlignmentX - $allowance));
+ $alignmentAreaRightX = min(($dimension - 1), ($estAlignmentX + $allowance));
+
+ if(($alignmentAreaRightX - $alignmentAreaLeftX) < ($overallEstModuleSize * 3)){
+ return null;
+ }
+
+ $alignmentAreaTopY = max(0, ($estAlignmentY - $allowance));
+ $alignmentAreaBottomY = min(($dimension - 1), ($estAlignmentY + $allowance));
+
+ if(($alignmentAreaBottomY - $alignmentAreaTopY) < ($overallEstModuleSize * 3)){
+ return null;
+ }
+
+ return (new AlignmentPatternFinder($this->matrix, $overallEstModuleSize))->find(
+ $alignmentAreaLeftX,
+ $alignmentAreaTopY,
+ ($alignmentAreaRightX - $alignmentAreaLeftX),
+ ($alignmentAreaBottomY - $alignmentAreaTopY),
+ );
+ }
+
+ /**
+ *
+ */
+ private function createTransform(
+ FinderPattern $nw,
+ FinderPattern $ne,
+ FinderPattern $sw,
+ int $size,
+ ?AlignmentPattern $ap = null
+ ):PerspectiveTransform{
+ $dimMinusThree = ($size - 3.5);
+
+ if($ap instanceof AlignmentPattern){
+ $bottomRightX = $ap->getX();
+ $bottomRightY = $ap->getY();
+ $sourceBottomRightX = ($dimMinusThree - 3.0);
+ $sourceBottomRightY = $sourceBottomRightX;
+ }
+ else{
+ // Don't have an alignment pattern, just make up the bottom-right point
+ $bottomRightX = ($ne->getX() - $nw->getX() + $sw->getX());
+ $bottomRightY = ($ne->getY() - $nw->getY() + $sw->getY());
+ $sourceBottomRightX = $dimMinusThree;
+ $sourceBottomRightY = $dimMinusThree;
+ }
+
+ return (new PerspectiveTransform)->quadrilateralToQuadrilateral(
+ 3.5,
+ 3.5,
+ $dimMinusThree,
+ 3.5,
+ $sourceBottomRightX,
+ $sourceBottomRightY,
+ 3.5,
+ $dimMinusThree,
+ $nw->getX(),
+ $nw->getY(),
+ $ne->getX(),
+ $ne->getY(),
+ $bottomRightX,
+ $bottomRightY,
+ $sw->getX(),
+ $sw->getY()
+ );
+ }
+
+}
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