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<?php |
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namespace Breadthe\PhpContrast; |
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class HexColorPair |
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{ |
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const MIN_RATIO = 3.0; |
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const MAX_RATIO = 4.5; // hard cap on the max requested ratio, to mitigate performance issues |
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public $ratio; // computed contrast ratio between fg : bg |
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// Calling these foreground/background instead of a more generic "color 1"/"color 2" |
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// Doesn't really matter, they can be used interchangeably |
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public $fg; // foreground (text) color |
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public $bg; // background color |
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protected $minRatio; |
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public function __construct(HexColor $fg = null, HexColor $bg = null) |
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{ |
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$this->fg = $fg; |
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$this->bg = $bg; |
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$this->ratio = static::calculateRatio($fg, $bg); |
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} |
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public static function make(HexColor $fg, HexColor $bg) |
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{ |
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return new static($fg, $bg); |
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} |
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public static function ratio(HexColor $fg, HexColor $bg) |
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{ |
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return (new static($fg, $bg))->ratio; |
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} |
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public static function random(): self |
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{ |
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return (new static)->getRandom(); |
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} |
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public static function sibling(string $hexValue): HexColor |
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{ |
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return (new static)->getSibling($hexValue); |
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} |
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public static function minContrast($ratio): self |
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{ |
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if ($ratio < self::MIN_RATIO) { |
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$ratio = self::MIN_RATIO; |
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} |
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if ($ratio > self::MAX_RATIO) { |
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$ratio = self::MAX_RATIO; |
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} |
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$pair = new static; |
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$pair->minRatio = $ratio; |
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return $pair; |
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} |
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public function getRandom(): self |
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{ |
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$minRatio = $this->minRatio ?? self::MIN_RATIO; |
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$fg = HexColor::random(); |
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return $this->getRandomPairMinRatio($fg, $minRatio); |
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} |
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public function getSibling(string $hexValue): HexColor |
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{ |
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$minRatio = $this->minRatio ?? self::MIN_RATIO; |
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$pair = $this->getRandomPairMinRatio(HexColor::make($hexValue), $minRatio); |
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return $pair->bg; |
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} |
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protected static function calculateRatio(HexColor $fg = null, HexColor $bg = null) |
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{ |
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if (! $fg || ! $bg) { |
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return; |
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} |
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$fgLuminance = static::luminance($fg); |
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$bgLuminance = static::luminance($bg); |
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return round((max($fgLuminance, $bgLuminance) + 0.05) / (min($fgLuminance, $bgLuminance) + 0.05) * 10) / 10; |
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} |
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protected static function luminance(HexColor $color) |
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{ |
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[$rHex, $gHex, $bHex] = static::rgbHexChannels($color); |
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// Get decimal values |
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$r8bit = base_convert($rHex, 16, 10); |
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$g8bit = base_convert($gHex, 16, 10); |
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$b8bit = base_convert($bHex, 16, 10); |
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// Get sRGB values |
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$rSrgb = $r8bit / 255; |
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$gSrgb = $g8bit / 255; |
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$bSrgb = $b8bit / 255; |
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// Calculate luminance |
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$r = ($rSrgb <= 0.03928) ? $rSrgb / 12.92 : pow((($rSrgb + 0.055) / 1.055), 2.4); |
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$g = ($gSrgb <= 0.03928) ? $gSrgb / 12.92 : pow((($gSrgb + 0.055) / 1.055), 2.4); |
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$b = ($bSrgb <= 0.03928) ? $bSrgb / 12.92 : pow((($bSrgb + 0.055) / 1.055), 2.4); |
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return 0.2126 * $r + 0.7152 * $g + 0.0722 * $b; |
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} |
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/** |
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* '#abcdef' => ['ab', 'cd', 'ef']. |
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*/ |
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protected static function rgbHexChannels(HexColor $hexColor): array |
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{ |
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$hex = substr($hexColor->hex, 1); // strip the # |
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return [ |
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substr($hex, 0, 2), |
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substr($hex, 2, 2), |
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substr($hex, 4, 2), |
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]; |
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} |
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protected function getRandomPairMinRatio($fg, $minRatio): self |
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{ |
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do { |
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$bg = HexColor::random(); |
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$pair = new static($fg, $bg); |
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} while ($pair->ratio <= $minRatio); |
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return $pair; |
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} |
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} |
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breadthe /
php-contrast
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This check marks access to variables or properties that have not been declared yet. While PHP has no explicit notion of declaring a variable, accessing it before a value is assigned to it is most likely a bug.