diff options
Diffstat (limited to 'apps/theming/lib/Util.php')
| -rw-r--r-- | apps/theming/lib/Util.php | 55 |
1 files changed, 51 insertions, 4 deletions
diff --git a/apps/theming/lib/Util.php b/apps/theming/lib/Util.php index 951b07bfa2a..c4f0123460e 100644 --- a/apps/theming/lib/Util.php +++ b/apps/theming/lib/Util.php @@ -57,7 +57,7 @@ class Util { * @return bool */ public function invertTextColor(string $color): bool { - return $this->isBrightColor($color); + return $this->colorContrast($color, '#ffffff') < 4.5; } /** @@ -81,7 +81,28 @@ class Util { * @param ?bool $brightBackground * @return string */ - public function elementColor($color, ?bool $brightBackground = null) { + public function elementColor($color, ?bool $brightBackground = null, ?string $backgroundColor = null) { + if ($backgroundColor !== null) { + $brightBackground = $brightBackground ?? $this->isBrightColor($backgroundColor); + // Minimal amount that is possible to change the luminance + $epsilon = 1.0 / 255.0; + // Current iteration to prevent infinite loops + $iteration = 0; + // We need to keep blurred backgrounds in mind which might be mixed with the background + $blurredBackground = $this->mix($backgroundColor, $brightBackground ? $color : '#ffffff', 66); + $contrast = $this->colorContrast($color, $blurredBackground); + + // Min. element contrast is 3:1 but we need to keep hover states in mind -> min 3.2:1 + while ($contrast < 3.2 && $iteration++ < 100) { + $hsl = Color::hexToHsl($color); + $hsl['L'] = max(0, min(1, $hsl['L'] + ($brightBackground ? -$epsilon : $epsilon))); + $color = '#' . Color::hslToHex($hsl); + $contrast = $this->colorContrast($color, $blurredBackground); + } + return $color; + } + + // Fallback for legacy calling $luminance = $this->calculateLuminance($color); if ($brightBackground !== false && $luminance > 0.8) { @@ -139,12 +160,38 @@ class Util { } /** + * Calculate the Luma according to WCAG 2 + * http://www.w3.org/TR/WCAG20/#relativeluminancedef * @param string $color rgb color value * @return float */ public function calculateLuma(string $color): float { - [$red, $green, $blue] = $this->hexToRGB($color); - return (0.2126 * $red + 0.7152 * $green + 0.0722 * $blue) / 255; + $rgb = $this->hexToRGB($color); + + // Normalize the values by converting to float and applying the rules from WCAG2.0 + $rgb = array_map(function (int $color) { + $color = $color / 255.0; + if ($color <= 0.03928) { + return $color / 12.92; + } else { + return pow((($color + 0.055) / 1.055), 2.4); + } + }, $rgb); + + [$red, $green, $blue] = $rgb; + return (0.2126 * $red + 0.7152 * $green + 0.0722 * $blue); + } + + /** + * Calculat the color contrast according to WCAG 2 + * http://www.w3.org/TR/WCAG20/#contrast-ratiodef + * @param string $color1 The first color + * @param string $color2 The second color + */ + public function colorContrast(string $color1, string $color2): float { + $luminance1 = $this->calculateLuma($color1) + 0.05; + $luminance2 = $this->calculateLuma($color2) + 0.05; + return max($luminance1, $luminance2) / min($luminance1, $luminance2); } /** |