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<?php |
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namespace Undemanding\Difference; |
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class ConnectedDifferences |
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{ |
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/** |
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* @var array |
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*/ |
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private $bitmap; |
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/** |
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* @var int |
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*/ |
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private $width; |
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/** |
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* @var int |
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*/ |
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private $height; |
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/** |
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* @var array |
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*/ |
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private $boundaries = []; |
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/** |
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* @param Difference $difference |
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*/ |
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public function __construct(Difference $difference) |
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{ |
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$this->bitmap = $difference->getBitmap(); |
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$this->width = $difference->getWidth(); |
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$this->height = $difference->getHeight(); |
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$this->boundaries = $this->findBoundaries(); |
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} |
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/** |
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* Find separate boundaries. |
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* |
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* @return array |
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*/ |
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private function findBoundaries() |
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{ |
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$pixels = []; |
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for ($y = 0; $y < $this->height; $y++) { |
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for ($x = 0; $x < $this->width; $x++) { |
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if ($this->bitmap[$y][$x] > 0) { |
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$pixels["{$x}:{$y}"] = [ |
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"group" => null, |
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"x" => $x, |
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"y" => $y, |
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]; |
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} |
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} |
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} |
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$group = 1; |
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$boundaries = []; |
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foreach ($pixels as $i => $pixel) { |
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$adjacent = $this->adjacent($pixel); |
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if (!$pixel["group"]) { |
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foreach ($adjacent as $key) { |
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if (isset($pixels[$key]) and $pixels[$key]["group"]) { |
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$pixel["group"] = $pixels[$key]["group"]; |
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} |
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} |
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} |
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if (!$pixel["group"]) { |
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$pixel["group"] = $group++; |
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} |
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foreach ($adjacent as $key) { |
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if (isset($pixels[$key])) { |
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$pixels[$key]["group"] = $pixel["group"]; |
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} |
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} |
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} |
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$groups = array_values(array_unique(array_map(function($pixel) { |
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return $pixel["group"]; |
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}, $pixels))); |
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foreach ($groups as $group) { |
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$filtered = array_filter($pixels, function($pixel) use ($group) { |
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return $pixel["group"] === $group; |
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}); |
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$ax = $this->width; |
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$bx = 0; |
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$ay = $this->height; |
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$by = 0; |
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foreach ($filtered as $pixel) { |
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$x = $pixel["x"]; |
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$y = $pixel["y"]; |
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if ($x > $bx) { |
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$bx = $x; |
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} |
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if ($x < $ax) { |
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$ax = $x; |
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} |
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if ($y > $by) { |
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$by = $y; |
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} |
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if ($y < $ay) { |
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$ay = $y; |
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} |
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} |
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array_push($boundaries, [ |
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"top" => $ay, |
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"right" => $bx, |
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"bottom" => $by, |
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"left" => $ax, |
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]); |
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} |
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return $boundaries; |
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} |
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/** |
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* @return ConnectedDifferences |
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*/ |
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public function withJoinedBoundaries() |
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{ |
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$keep = []; |
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foreach ($this->boundaries as $boundary) { |
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foreach ($keep as $i => $kept) { |
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if ($this->intersect($boundary, $kept)) { |
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View Code Duplication |
if ($boundary["top"] < $kept["top"]) { |
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$keep[$i]["top"] = $boundary["top"]; |
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} |
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View Code Duplication |
if ($boundary["right"] > $kept["right"]) { |
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$keep[$i]["right"] = $boundary["right"]; |
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} |
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View Code Duplication |
if ($boundary["bottom"] > $kept["bottom"]) { |
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$keep[$i]["bottom"] = $boundary["bottom"]; |
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} |
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View Code Duplication |
if ($boundary["left"] < $kept["left"]) { |
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$keep[$i]["left"] = $boundary["left"]; |
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} |
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continue 2; |
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} |
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} |
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array_push($keep, $boundary); |
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} |
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return $this->cloneWith("boundaries", $keep); |
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} |
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/** |
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* @param string $property |
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* @param mixed $value |
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* |
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* @return ConnectedDifferences |
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*/ |
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private function cloneWith($property, $value) |
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{ |
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$clone = clone $this; |
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$clone->$property = $value; |
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return $clone; |
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} |
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/** |
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* Labels for adjacent pixels. |
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* |
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* @param array $pixel |
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* |
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* @return array |
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*/ |
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private function adjacent($pixel) |
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{ |
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$adjacent = [ |
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($pixel["x"] - 1) . ":" . ($pixel["y"] - 1), |
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($pixel["x"] - 1) . ":" . $pixel["y"], |
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($pixel["x"] - 1) . ":" . ($pixel["y"] + 1), |
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$pixel["x"] . ":" . ($pixel["y"] - 1), |
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$pixel["x"] . ":" . ($pixel["y"] + 1), |
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($pixel["x"] + 1) . ":" . ($pixel["y"] - 1), |
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($pixel["x"] + 1) . ":" . $pixel["y"], |
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($pixel["x"] + 1) . ":" . ($pixel["y"] + 1), |
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]; |
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return $adjacent; |
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} |
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/** |
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* Tell if two boundaries overlap. |
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* |
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* @param array $p |
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* @param array $q |
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* |
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* @return bool |
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*/ |
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private function intersect(array $p, array $q) |
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{ |
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return max($p["left"], $q["left"]) <= min($p["right"], $q["right"]) and max($p["top"], $q["top"]) <= min($p["bottom"], $q["bottom"]); |
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} |
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/** |
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* @return array |
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*/ |
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public function boundaries() |
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{ |
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return $this->boundaries; |
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} |
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} |
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PHP has two types of connecting operators (logical operators, and boolean operators):
and&&or||The difference between these is the order in which they are executed. In most cases, you would want to use a boolean operator like
&&, or||.Let’s take a look at a few examples:
Logical Operators are used for Control-Flow
One case where you explicitly want to use logical operators is for control-flow such as this:
Since
dieintroduces problems of its own, f.e. it makes our code hardly testable, and prevents any kind of more sophisticated error handling; you probably do not want to use this in real-world code. Unfortunately, logical operators cannot be combined withthrowat this point:These limitations lead to logical operators rarely being of use in current PHP code.