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<?php |
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|
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namespace FluentCart\App\Services\Theme; |
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|
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/** |
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* Colour maths for the storefront palette. |
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* |
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* A block theme hands us a handful of palette colours. The storefront needs a |
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* coherent set of surfaces, borders, muted text and accent tints. Rather than |
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* invent those, we derive them from the colours the theme actually declares — |
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* a border is the body text mixed most of the way toward the surface, a muted |
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* text tone is the same mix stopped earlier, and button text is whichever of |
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* light/dark reads better on the button it sits on. |
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* |
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* All maths is sRGB. Luminance follows the WCAG 2.x relative-luminance |
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* definition so the contrast picks match what an accessibility checker sees. |
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*/ |
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class ColorMath |
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{ |
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/** |
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* Parse a colour into an RGB triplet. |
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* |
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* Accepts #rgb, #rrggbb, #rrggbbaa and rgb()/rgba(). Returns null for |
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* anything unreadable so callers can fall back instead of guessing. |
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* |
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* @param string $color |
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* @return array|null [r, g, b] or null |
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*/ |
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public static function parse($color): ?array |
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{ |
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$color = trim((string)$color); |
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|
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if ($color === '') { |
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return null; |
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} |
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|
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if (preg_match('/^#([0-9a-f]{3})$/i', $color, $matches)) { |
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$shorthand = $matches[1]; |
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|
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return [ |
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hexdec(str_repeat($shorthand[0], 2)), |
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hexdec(str_repeat($shorthand[1], 2)), |
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hexdec(str_repeat($shorthand[2], 2)), |
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]; |
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} |
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|
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if (preg_match('/^#([0-9a-f]{6})(?:[0-9a-f]{2})?$/i', $color, $matches)) { |
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$sixDigit = $matches[1]; |
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|
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return [ |
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hexdec(substr($sixDigit, 0, 2)), |
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hexdec(substr($sixDigit, 2, 2)), |
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hexdec(substr($sixDigit, 4, 2)), |
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]; |
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} |
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|
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if (preg_match('/^rgba?\(\s*([0-9.]+)[\s,]+([0-9.]+)[\s,]+([0-9.]+)/i', $color, $matches)) { |
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return [ |
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(int)round((float)$matches[1]), |
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(int)round((float)$matches[2]), |
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(int)round((float)$matches[3]), |
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]; |
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} |
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|
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return null; |
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} |
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|
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/** |
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* Convert an RGB triplet to #rrggbb. |
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* |
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* @param array $rgb |
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* @return string |
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*/ |
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public static function toHex(array $rgb): string |
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{ |
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$hex = '#'; |
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|
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foreach (array_slice($rgb, 0, 3) as $channel) { |
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$channel = max(0, min(255, (int)round($channel))); |
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$hex .= str_pad(dechex($channel), 2, '0', STR_PAD_LEFT); |
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} |
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|
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return $hex; |
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} |
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|
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/** |
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* Normalise any readable colour to #rrggbb. |
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* |
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* @param string $color |
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* @param string $fallback Returned when the colour cannot be parsed. |
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* @return string |
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*/ |
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public static function hex($color, string $fallback = ''): string |
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{ |
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$rgb = self::parse($color); |
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|
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return $rgb ? self::toHex($rgb) : $fallback; |
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} |
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|
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/** |
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* Mix two colours. |
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* |
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* @param string $first |
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* @param string $second |
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* @param int $percent How much of $first to keep, 0-100. |
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* @return string Hex, or '' when neither colour is readable. |
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*/ |
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public static function mix($first, $second, int $percent = 50): string |
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{ |
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$firstRgb = self::parse($first); |
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$secondRgb = self::parse($second); |
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|
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if (!$firstRgb || !$secondRgb) { |
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return self::hex($firstRgb ? $first : $second); |
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} |
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|
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$ratio = max(0, min(100, $percent)) / 100; |
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$mixed = []; |
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|
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for ($channel = 0; $channel < 3; $channel++) { |
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$mixed[$channel] = ($firstRgb[$channel] * $ratio) + ($secondRgb[$channel] * (1 - $ratio)); |
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} |
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|
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return self::toHex($mixed); |
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} |
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|
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/** |
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* WCAG relative luminance. |
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* |
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* @param string $color |
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* @return float 0-1, or -1 when the colour cannot be read. |
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*/ |
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public static function luminance($color): float |
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{ |
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$rgb = self::parse($color); |
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|
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if (!$rgb) { |
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return -1.0; |
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} |
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|
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$linear = []; |
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|
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foreach (array_slice($rgb, 0, 3) as $channel) { |
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$channel = $channel / 255; |
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$linear[] = $channel <= 0.03928 |
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? $channel / 12.92 |
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: pow(($channel + 0.055) / 1.055, 2.4); |
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} |
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return (0.2126 * $linear[0]) + (0.7152 * $linear[1]) + (0.0722 * $linear[2]); |
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} |
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|
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/** |
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* Whether a colour reads as dark. |
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* |
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* The 0.45 threshold sits above the midpoint on purpose: mid-tone brand |
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* colours read as "dark" to the eye well before their luminance halves. |
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* |
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* @param string $color |
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* @return bool |
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*/ |
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public static function isDark($color): bool |
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{ |
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$luminance = self::luminance($color); |
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|
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return $luminance >= 0 && $luminance < 0.45; |
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} |
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|
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/** |
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* WCAG contrast ratio between two colours. |
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* |
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* @param string $first |
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* @param string $second |
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* @return float 1-21, or 0 when either colour cannot be read. |
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*/ |
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public static function contrast($first, $second): float |
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{ |
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$firstLuminance = self::luminance($first); |
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$secondLuminance = self::luminance($second); |
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|
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if ($firstLuminance < 0 || $secondLuminance < 0) { |
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return 0.0; |
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} |
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|
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$lighter = max($firstLuminance, $secondLuminance); |
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$darker = min($firstLuminance, $secondLuminance); |
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return ($lighter + 0.05) / ($darker + 0.05); |
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} |
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|
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/** |
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* Pick whichever of two text colours reads better on a background. |
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* |
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* @param string $background |
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* @param string $light |
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* @param string $dark |
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* @return string |
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*/ |
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public static function readableOn($background, string $light = '#ffffff', string $dark = '#1f2937'): string |
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{ |
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return self::contrast($background, $light) >= self::contrast($background, $dark) ? $light : $dark; |
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} |
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|
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/** |
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* A text colour that reads on a background (WCAG 4.5:1) wherever one can. |
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* |
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* readableOn()'s usual pair is kept whenever it reads, so every partner it |
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* already made readable is unchanged. On a mid-tone background neither |
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* half of that pair reaches 4.5:1 (#809400 peaks at 4.30:1 with #1f2937); |
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* pure black or white — whichever reads better — goes further, and is |
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* taken only when it does. |
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* |
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* @param string $background |
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* @return string |
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*/ |
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public static function readableText($background): string |
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{ |
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$picked = self::readableOn($background); |
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$pickedContrast = self::contrast($background, $picked); |
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|
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if ($pickedContrast >= 4.5) { |
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return $picked; |
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} |
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|
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$extreme = self::contrast($background, '#ffffff') >= self::contrast($background, '#000000') |
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? '#ffffff' |
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: '#000000'; |
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|
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return self::contrast($background, $extreme) > $pickedContrast ? $extreme : $picked; |
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} |
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|
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/** |
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* Mix text into a surface, keeping as little of the text as still reads. |
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* |
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* Starts at $percent of the text and moves toward it in small steps until |
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* the mix reaches $minimum contrast on the surface — a mix that already |
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* reads is returned unchanged. Text that does not read on the surface |
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* itself comes back as the text: nothing between the two reads better. |
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* |
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* @param string $text |
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* @param string $surface |
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* @param int $percent Starting share of the text, 0-100. |
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* @param float $minimum |
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* @return string Hex, or '' when either colour is unreadable. |
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*/ |
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public static function readableMix($text, $surface, int $percent, float $minimum = 4.5): string |
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{ |
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if (!self::parse($text) || !self::parse($surface)) { |
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return ''; |
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} |
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|
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for ($share = max(0, $percent); $share < 100; $share += 2) { |
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$mixed = self::mix($text, $surface, $share); |
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|
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if (self::contrast($surface, $mixed) >= $minimum) { |
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return $mixed; |
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} |
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} |
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|
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return self::hex($text); |
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} |
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|
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/** |
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* Move a colour away from itself — lighter when it is dark, darker when it |
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* is light. How a hover is derived from a button that states none. |
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* |
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* @param string $color |
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* @param int $percent |
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* @return string |
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*/ |
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public static function shiftFromItself($color, int $percent = 12): string |
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{ |
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return self::isDark($color) |
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? self::lighten($color, $percent) |
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: self::darken($color, $percent); |
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} |
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|
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/** |
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* Nudge a colour toward white. |
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* |
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* @param string $color |
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* @param int $percent |
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* @return string |
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*/ |
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public static function lighten($color, int $percent): string |
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{ |
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return self::mix('#ffffff', $color, $percent); |
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} |
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|
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/** |
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* Nudge a colour toward black. |
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* |
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* @param string $color |
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* @param int $percent |
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* @return string |
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*/ |
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public static function darken($color, int $percent): string |
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{ |
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return self::mix('#000000', $color, $percent); |
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} |
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|
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/** |
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* Move a colour away from the surface it sits on, so it stays visible on |
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* a light or a dark background without the caller knowing which it has. |
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* |
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* @param string $color |
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* @param string $background |
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* @param int $percent |
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* @return string |
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*/ |
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public static function awayFrom($color, $background, int $percent): string |
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{ |
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return self::isDark($background) |
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? self::lighten($color, $percent) |
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: self::darken($color, $percent); |
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} |
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} |
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|
