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<?php
/**
* Class GridSampler
*
* @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\Data\QRMatrix;
use chillerlan\QRCode\Decoder\BitMatrix;
use function array_fill, count, intdiv, sprintf;
/**
* 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 #setGridSampler(GridSampler)
* with an instance of a class which implements this interface.
*
* @author Sean Owen
*/
final class GridSampler{
private array $points;
/**
* 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.
*
* 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.
*
* 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.
*
* @param int $dimension matrix width/height
*
* @throws \chillerlan\QRCode\Detector\QRCodeDetectorException if an endpoint is lies outside the image boundaries
*/
private function checkAndNudgePoints(int $dimension):void{
$nudged = true;
$max = count($this->points);
// Check and nudge points from start until we see some that are OK:
for($offset = 0; $offset < $max && $nudged; $offset += 2){
$x = (int)$this->points[$offset];
$y = (int)$this->points[($offset + 1)];
if($x < -1 || $x > $dimension || $y < -1 || $y > $dimension){
throw new QRCodeDetectorException(sprintf('checkAndNudgePoints 1, x: %s, y: %s, d: %s', $x, $y, $dimension));
}
$nudged = false;
if($x === -1){
$this->points[$offset] = 0.0;
$nudged = true;
}
elseif($x === $dimension){
$this->points[$offset] = ($dimension - 1);
$nudged = true;
}
if($y === -1){
$this->points[($offset + 1)] = 0.0;
$nudged = true;
}
elseif($y === $dimension){
$this->points[($offset + 1)] = ($dimension - 1);
$nudged = true;
}
}
// Check and nudge points from end:
$nudged = true;
for($offset = ($max - 2); $offset >= 0 && $nudged; $offset -= 2){
$x = (int)$this->points[$offset];
$y = (int)$this->points[($offset + 1)];
if($x < -1 || $x > $dimension || $y < -1 || $y > $dimension){
throw new QRCodeDetectorException(sprintf('checkAndNudgePoints 2, x: %s, y: %s, d: %s', $x, $y, $dimension));
}
$nudged = false;
if($x === -1){
$this->points[$offset] = 0.0;
$nudged = true;
}
elseif($x === $dimension){
$this->points[$offset] = ($dimension - 1);
$nudged = true;
}
if($y === -1){
$this->points[($offset + 1)] = 0.0;
$nudged = true;
}
elseif($y === $dimension){
$this->points[($offset + 1)] = ($dimension - 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.
*
* @return \chillerlan\QRCode\Decoder\BitMatrix representing a grid of points sampled from the image within a region
* defined by the "from" parameters
* @throws \chillerlan\QRCode\Detector\QRCodeDetectorException 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 function sampleGrid(BitMatrix $matrix, int $dimension, PerspectiveTransform $transform):BitMatrix{
if($dimension <= 0){
throw new QRCodeDetectorException('invalid matrix size');
}
$bits = new BitMatrix($dimension);
$this->points = array_fill(0, (2 * $dimension), 0.0);
for($y = 0; $y < $dimension; $y++){
$max = count($this->points);
$iValue = ($y + 0.5);
for($x = 0; $x < $max; $x += 2){
$this->points[$x] = (($x / 2) + 0.5);
$this->points[($x + 1)] = $iValue;
}
// phpcs:ignore
[$this->points, ] = $transform->transformPoints($this->points);
// Quick check to see if points transformed to something inside the image;
// sufficient to check the endpoints
$this->checkAndNudgePoints($matrix->getSize());
// no need to try/catch as QRMatrix::set() will silently discard out of bounds values
# try{
for($x = 0; $x < $max; $x += 2){
// Black(-ish) pixel
$bits->set(
intdiv($x, 2),
$y,
$matrix->check((int)$this->points[$x], (int)$this->points[($x + 1)]),
QRMatrix::M_DATA
);
}
# }
# catch(\Throwable $aioobe){//ArrayIndexOutOfBoundsException
// This feels wrong, but, sometimes if the finder patterns are misidentified, the resulting
// transform gets "twisted" such that it maps a straight line of points to a set of points
// whose endpoints are in bounds, but others are not. There is probably some mathematical
// way to detect this about the transformation that I don't know yet.
// This results in an ugly runtime exception despite our clever checks above -- can't have
// that. We could check each point's coordinates but that feels duplicative. We settle for
// catching and wrapping ArrayIndexOutOfBoundsException.
# throw new QRCodeDetectorException('ArrayIndexOutOfBoundsException');
# }
}
return $bits;
}
}
|
