From 37bdbc10a989b6bc6f2ff25bcf6d09d9c7217783 Mon Sep 17 00:00:00 2001
From: Marcel Werk <burntime@woltlab.com>
Date: Thu, 8 Oct 2026 15:12:38 +0200
Subject: [PATCH 1/2] Generate individual default cover photos for users based
 on the style colors

---
 .../templates/userProfileHeader.tpl           |   2 +-
 .../files/lib/data/user/UserProfile.class.php |  16 +-
 .../photo/GeneratedUserCoverPhoto.class.php   |  39 +++
 .../generator/CoverPhotoGenerator.class.php   | 310 ++++++++++++++++++
 .../generator/CoverPhotoPalette.class.php     |  43 +++
 .../photo/generator/OklchColor.class.php      | 166 ++++++++++
 6 files changed, 573 insertions(+), 3 deletions(-)
 create mode 100644 wcfsetup/install/files/lib/data/user/cover/photo/GeneratedUserCoverPhoto.class.php
 create mode 100644 wcfsetup/install/files/lib/system/image/cover/photo/generator/CoverPhotoGenerator.class.php
 create mode 100644 wcfsetup/install/files/lib/system/image/cover/photo/generator/CoverPhotoPalette.class.php
 create mode 100644 wcfsetup/install/files/lib/system/image/cover/photo/generator/OklchColor.class.php

diff --git a/com.woltlab.wcf/templates/userProfileHeader.tpl b/com.woltlab.wcf/templates/userProfileHeader.tpl
index abf18ae8c4a..c89e47c2d6b 100644
--- a/com.woltlab.wcf/templates/userProfileHeader.tpl
+++ b/com.woltlab.wcf/templates/userProfileHeader.tpl
@@ -30,7 +30,7 @@
 			{if $view->canEditCoverPhoto()}
 				<ul class="userProfileManageCoverPhoto buttonGroup buttonList smallButtons">
 					<li>
-						<button type="button" data-edit-cover-photo="{link controller="UserCoverPhoto" id=$user->userID}{/link}" data-default-cover-photo="{$__wcf->styleHandler->getStyle()->getCoverPhotoUrl()}" class="button small">
+						<button type="button" data-edit-cover-photo="{link controller="UserCoverPhoto" id=$user->userID}{/link}" data-default-cover-photo="{$view->user->getDefaultCoverPhoto()->getURL()}" class="button small">
 							{icon name='camera'}
 							<span>{lang}wcf.user.coverPhoto.edit{/lang}</span>
 						</button>
diff --git a/wcfsetup/install/files/lib/data/user/UserProfile.class.php b/wcfsetup/install/files/lib/data/user/UserProfile.class.php
index 142e68e7919..0b583d5dda7 100644
--- a/wcfsetup/install/files/lib/data/user/UserProfile.class.php
+++ b/wcfsetup/install/files/lib/data/user/UserProfile.class.php
@@ -11,7 +11,7 @@
 use wcf\data\user\avatar\DefaultAvatar;
 use wcf\data\user\avatar\IUserAvatar;
 use wcf\data\user\avatar\StaticAvatar;
-use wcf\data\user\cover\photo\DefaultUserCoverPhoto;
+use wcf\data\user\cover\photo\GeneratedUserCoverPhoto;
 use wcf\data\user\cover\photo\IUserCoverPhoto;
 use wcf\data\user\cover\photo\UserCoverPhoto;
 use wcf\data\user\group\UserGroup;
@@ -437,13 +437,25 @@ public function getCoverPhoto(bool $isACP = false)
 
             // use default cover photo
             if ($this->coverPhoto === null) {
-                $this->coverPhoto = new DefaultUserCoverPhoto();
+                $this->coverPhoto = $this->getDefaultCoverPhoto();
             }
         }
 
         return $this->coverPhoto;
     }
 
+    /**
+     * Returns the cover photo that is shown if the user has no cover photo. Styles
+     * with a custom cover photo use it for all users, otherwise an individual
+     * cover photo is generated for each user.
+     *
+     * @since 6.3
+     */
+    public function getDefaultCoverPhoto(): IUserCoverPhoto
+    {
+        return new GeneratedUserCoverPhoto($this->username);
+    }
+
     /**
      * Returns true if the active user can view the cover photo of this user.
      *
diff --git a/wcfsetup/install/files/lib/data/user/cover/photo/GeneratedUserCoverPhoto.class.php b/wcfsetup/install/files/lib/data/user/cover/photo/GeneratedUserCoverPhoto.class.php
new file mode 100644
index 00000000000..c546a0a9130
--- /dev/null
+++ b/wcfsetup/install/files/lib/data/user/cover/photo/GeneratedUserCoverPhoto.class.php
@@ -0,0 +1,39 @@
+<?php
+
+namespace wcf\data\user\cover\photo;
+
+use wcf\system\image\cover\photo\generator\CoverPhotoGenerator;
+use wcf\system\style\StyleHandler;
+
+/**
+ * Represents a default cover photo that is generated for each user individually.
+ * Styles with a custom cover photo use it for all users instead.
+ *
+ * @author      Marcel Werk
+ * @copyright   2001-2026 WoltLab GmbH
+ * @license     GNU Lesser General Public License <http://opensource.org/licenses/lgpl-license.php>
+ * @since       6.3
+ */
+final class GeneratedUserCoverPhoto extends DefaultUserCoverPhoto
+{
+    private string $url;
+
+    public function __construct(
+        private readonly string $username,
+    ) {}
+
+    #[\Override]
+    public function getURL(?bool $forceWebP = null): string
+    {
+        // The style is resolved lazily to avoid side effects when only the object is needed.
+        if (StyleHandler::getInstance()->getStyle()->coverPhotoExtension !== '') {
+            return parent::getURL($forceWebP);
+        }
+
+        if (!isset($this->url)) {
+            $this->url = CoverPhotoGenerator::forActiveStyle()->getDataUri('user-' . \mb_strtolower($this->username));
+        }
+
+        return $this->url;
+    }
+}
diff --git a/wcfsetup/install/files/lib/system/image/cover/photo/generator/CoverPhotoGenerator.class.php b/wcfsetup/install/files/lib/system/image/cover/photo/generator/CoverPhotoGenerator.class.php
new file mode 100644
index 00000000000..796440cf201
--- /dev/null
+++ b/wcfsetup/install/files/lib/system/image/cover/photo/generator/CoverPhotoGenerator.class.php
@@ -0,0 +1,310 @@
+<?php
+
+namespace wcf\system\image\cover\photo\generator;
+
+use Random\Engine\Xoshiro256StarStar;
+use Random\Randomizer;
+use wcf\system\style\StyleHandler;
+
+/**
+ * Generates abstract SVG cover photos that are derived from a seed, the same
+ * seed always yields the same image. The colors are taken from the style, the
+ * hue is slightly shifted for each seed to create some variety.
+ *
+ * @author      Marcel Werk
+ * @copyright   2001-2026 WoltLab GmbH
+ * @license     GNU Lesser General Public License <http://opensource.org/licenses/lgpl-license.php>
+ * @since       6.3
+ */
+final class CoverPhotoGenerator
+{
+    public const WIDTH = 1000;
+
+    public const HEIGHT = 400;
+
+    private static CoverPhotoGenerator $activeStyleGenerator;
+
+    /**
+     * @param ?CoverPhotoPalette $darkPalette palette that is used if the browser prefers a dark color scheme
+     */
+    public function __construct(
+        private readonly CoverPhotoPalette $palette,
+        private readonly ?CoverPhotoPalette $darkPalette = null,
+    ) {}
+
+    /**
+     * Returns the generator that uses the colors of the active style and
+     * respects the color scheme of the active user.
+     */
+    public static function forActiveStyle(): self
+    {
+        if (!isset(self::$activeStyleGenerator)) {
+            $styleHandler = StyleHandler::getInstance();
+            $style = $styleHandler->getStyle()->getDecoratedObject();
+
+            self::$activeStyleGenerator = match ($styleHandler->getColorScheme()) {
+                'dark' => new self(CoverPhotoPalette::fromStyle($style, true)),
+                'system' => new self(
+                    CoverPhotoPalette::fromStyle($style),
+                    $style->hasDarkMode !== 0 ? CoverPhotoPalette::fromStyle($style, true) : null,
+                ),
+                default => new self(CoverPhotoPalette::fromStyle($style)),
+            };
+        }
+
+        return self::$activeStyleGenerator;
+    }
+
+    /**
+     * Returns the cover photo for the given seed as a data URI.
+     */
+    public function getDataUri(string $seed): string
+    {
+        return 'data:image/svg+xml;base64,' . \base64_encode($this->render($seed));
+    }
+
+    /**
+     * Returns the SVG markup of the cover photo for the given seed.
+     */
+    public function render(string $seed): string
+    {
+        $randomizer = new Randomizer(new Xoshiro256StarStar(\hash('sha256', $seed, true)));
+
+        $hueShift = $randomizer->getFloat(-45, 45);
+        $css = 'svg{' . $this->getColorVariables($this->palette, $hueShift) . '}';
+        if ($this->darkPalette !== null) {
+            $css .= '@media (prefers-color-scheme:dark){svg{'
+                . $this->getColorVariables($this->darkPalette, $hueShift)
+                . '}}';
+        }
+
+        // Direction of the background gradient.
+        [$x1, $y1, $x2, $y2] = [
+            [0, 0, 1, 1],
+            [1, 0, 0, 1],
+            [0, 0, 1, 0],
+            [0, 1, 1, 0],
+        ][$randomizer->getInt(0, 3)];
+
+        $shapes = match ($randomizer->getInt(0, 4)) {
+            0 => $this->renderWaves($randomizer),
+            1 => $this->renderGlows($randomizer),
+            2 => $this->renderBands($randomizer),
+            3 => $this->renderCircles($randomizer),
+            4 => $this->renderFacets($randomizer),
+        };
+
+        $width = self::WIDTH;
+        $height = self::HEIGHT;
+
+        return <<<SVG
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 {$width} {$height}" width="{$width}" height="{$height}" preserveAspectRatio="xMidYMid slice"><style>{$css}</style><linearGradient id="g" x1="{$x1}" y1="{$y1}" x2="{$x2}" y2="{$y2}"><stop offset="0" style="stop-color:var(--c0)"/><stop offset="1" style="stop-color:var(--c1)"/></linearGradient><rect width="{$width}" height="{$height}" fill="url(#g)"/>{$shapes}</svg>
+SVG;
+    }
+
+    /**
+     * Derives the five colors `--c0` to `--c4` from the palette. The first two
+     * are used for the background, the remaining ones for the shapes.
+     */
+    private function getColorVariables(CoverPhotoPalette $palette, float $hueShift): string
+    {
+        $primary = $palette->primary->rotateHue($hueShift);
+        $accent = $palette->accent->rotateHue($hueShift);
+
+        $colors = [
+            $primary,
+            $primary->rotateHue(30)->withLightness($primary->lightness - 0.08),
+            $accent,
+            $accent->rotateHue(-35)->withLightness($accent->lightness + 0.1),
+            $primary->rotateHue(-30)->withLightness($primary->lightness + 0.18),
+        ];
+
+        $variables = '';
+        foreach ($colors as $index => $color) {
+            $variables .= "--c{$index}:{$color->toHex()};";
+        }
+
+        return $variables;
+    }
+
+    /**
+     * Layered waves that stretch across the entire width.
+     */
+    private function renderWaves(Randomizer $randomizer): string
+    {
+        $layers = $randomizer->getInt(3, 4);
+        $colorOffset = $randomizer->getInt(0, 2);
+
+        $svg = '';
+        for ($i = 0; $i < $layers; $i++) {
+            $baseline = self::HEIGHT * (0.25 + 0.6 * $i / ($layers - 1));
+            $amplitude = $randomizer->getInt(25, 70);
+            $y = static fn() => (int)\round($baseline + $randomizer->getInt(-$amplitude, $amplitude));
+
+            $path = \sprintf(
+                'M0 %d C%d %d %d %d 500 %d S%d %d 1000 %dV%dH0Z',
+                $y(),
+                $randomizer->getInt(120, 220),
+                $y(),
+                $randomizer->getInt(280, 380),
+                $y(),
+                $y(),
+                $randomizer->getInt(780, 880),
+                $y(),
+                $y(),
+                self::HEIGHT,
+            );
+
+            $svg .= '<path d="' . $path . '" style="' . $this->fill(2 + ($i + $colorOffset) % 3, 0.35 + 0.15 * $i) . '"/>';
+        }
+
+        return $svg;
+    }
+
+    /**
+     * Soft glows that blend into each other.
+     */
+    private function renderGlows(Randomizer $randomizer): string
+    {
+        $svg = '';
+        foreach ([2, 3, 4] as $color) {
+            $svg .= <<<SVG
+<radialGradient id="r{$color}"><stop offset="0" style="stop-color:var(--c{$color})"/><stop offset="1" style="stop-color:var(--c{$color});stop-opacity:0"/></radialGradient>
+SVG;
+        }
+
+        $count = $randomizer->getInt(4, 6);
+        for ($i = 0; $i < $count; $i++) {
+            $svg .= \sprintf(
+                '<circle cx="%d" cy="%d" r="%d" fill="url(#r%d)" opacity="%s"/>',
+                $randomizer->getInt(0, self::WIDTH),
+                $randomizer->getInt(-50, self::HEIGHT + 50),
+                $randomizer->getInt(150, 350),
+                $randomizer->getInt(2, 4),
+                $this->opacity($randomizer->getFloat(0.5, 0.9)),
+            );
+        }
+
+        return $svg;
+    }
+
+    /**
+     * Diagonal bands of varying width.
+     */
+    private function renderBands(Randomizer $randomizer): string
+    {
+        $angle = $randomizer->getInt(20, 70) * ($randomizer->getInt(0, 1) === 0 ? 1 : -1);
+
+        $svg = \sprintf('<g transform="rotate(%d %d %d)">', $angle, self::WIDTH / 2, self::HEIGHT / 2);
+        $x = -400 + $randomizer->getInt(0, 100);
+        while ($x < self::WIDTH + 400) {
+            $width = $randomizer->getInt(30, 180);
+            $svg .= \sprintf(
+                '<rect x="%d" y="-600" width="%d" height="1600" style="%s"/>',
+                $x,
+                $width,
+                $this->fill($randomizer->getInt(2, 4), $randomizer->getFloat(0.15, 0.45)),
+            );
+            $x += $width + $randomizer->getInt(20, 120);
+        }
+
+        return $svg . '</g>';
+    }
+
+    /**
+     * Scattered circles of different sizes.
+     */
+    private function renderCircles(Randomizer $randomizer): string
+    {
+        $svg = '';
+        $count = $randomizer->getInt(14, 22);
+        for ($i = 0; $i < $count; $i++) {
+            $svg .= \sprintf(
+                '<circle cx="%d" cy="%d" r="%d" style="%s"/>',
+                $randomizer->getInt(0, self::WIDTH),
+                $randomizer->getInt(0, self::HEIGHT),
+                $randomizer->getInt(15, 110),
+                $this->fill($randomizer->getInt(2, 4), $randomizer->getFloat(0.15, 0.5)),
+            );
+        }
+
+        return $svg;
+    }
+
+    /**
+     * Low poly facets that lighten or darken the background.
+     */
+    private function renderFacets(Randomizer $randomizer): string
+    {
+        $columns = 8;
+        $rows = 4;
+        $cellWidth = self::WIDTH / $columns;
+        $cellHeight = self::HEIGHT / $rows;
+
+        $points = [];
+        for ($row = 0; $row <= $rows; $row++) {
+            for ($column = 0; $column <= $columns; $column++) {
+                $x = $column * $cellWidth;
+                $y = $row * $cellHeight;
+
+                // Only move the inner points to keep the edges straight.
+                if ($column !== 0 && $column !== $columns) {
+                    $x += $randomizer->getFloat(-0.35, 0.35) * $cellWidth;
+                }
+                if ($row !== 0 && $row !== $rows) {
+                    $y += $randomizer->getFloat(-0.35, 0.35) * $cellHeight;
+                }
+
+                $points[$row][$column] = (int)\round($x) . ' ' . (int)\round($y);
+            }
+        }
+
+        // Triangles are grouped by their shade to keep the markup small.
+        $shades = [
+            1 => ['#fff', 0.06, ''],
+            2 => ['#fff', 0.12, ''],
+            3 => ['#000', 0.06, ''],
+            4 => ['#000', 0.12, ''],
+        ];
+        for ($row = 0; $row < $rows; $row++) {
+            for ($column = 0; $column < $columns; $column++) {
+                $topLeft = $points[$row][$column];
+                $topRight = $points[$row][$column + 1];
+                $bottomLeft = $points[$row + 1][$column];
+                $bottomRight = $points[$row + 1][$column + 1];
+
+                if ($randomizer->getInt(0, 1) === 0) {
+                    $triangles = [[$topLeft, $topRight, $bottomRight], [$topLeft, $bottomRight, $bottomLeft]];
+                } else {
+                    $triangles = [[$topLeft, $topRight, $bottomLeft], [$topRight, $bottomRight, $bottomLeft]];
+                }
+
+                foreach ($triangles as [$a, $b, $c]) {
+                    $shade = $randomizer->getInt(0, 4);
+                    if ($shade !== 0) {
+                        $shades[$shade][2] .= "M{$a}L{$b}L{$c}Z";
+                    }
+                }
+            }
+        }
+
+        $svg = '';
+        foreach ($shades as [$color, $opacity, $path]) {
+            if ($path !== '') {
+                $svg .= \sprintf('<path d="%s" fill="%s" fill-opacity="%s"/>', $path, $color, $opacity);
+            }
+        }
+
+        return $svg;
+    }
+
+    private function fill(int $color, float $opacity): string
+    {
+        return "fill:var(--c{$color});fill-opacity:{$this->opacity($opacity)}";
+    }
+
+    private function opacity(float $opacity): string
+    {
+        return (string)\round($opacity, 2);
+    }
+}
diff --git a/wcfsetup/install/files/lib/system/image/cover/photo/generator/CoverPhotoPalette.class.php b/wcfsetup/install/files/lib/system/image/cover/photo/generator/CoverPhotoPalette.class.php
new file mode 100644
index 00000000000..add82380a0b
--- /dev/null
+++ b/wcfsetup/install/files/lib/system/image/cover/photo/generator/CoverPhotoPalette.class.php
@@ -0,0 +1,43 @@
+<?php
+
+namespace wcf\system\image\cover\photo\generator;
+
+use wcf\data\style\Style;
+
+/**
+ * Base colors of generated cover photos, derived from the style.
+ *
+ * @author      Marcel Werk
+ * @copyright   2001-2026 WoltLab GmbH
+ * @license     GNU Lesser General Public License <http://opensource.org/licenses/lgpl-license.php>
+ * @since       6.3
+ */
+final class CoverPhotoPalette
+{
+    public function __construct(
+        public readonly OklchColor $primary,
+        public readonly OklchColor $accent,
+    ) {}
+
+    public static function fromStyle(Style $style, bool $darkMode = false): self
+    {
+        $prefix = $darkMode ? Style::DARK_MODE_PREFIX : '';
+
+        return new self(
+            self::getColor($style, $prefix, 'wcfHeaderBackground', OklchColor::fromRgb(58, 109, 156)),
+            self::getColor($style, $prefix, 'wcfButtonPrimaryBackground', OklchColor::fromRgb(29, 122, 197)),
+        );
+    }
+
+    private static function getColor(Style $style, string $prefix, string $variableName, OklchColor $fallback): OklchColor
+    {
+        $value = $style->getVariable($prefix . $variableName, true);
+
+        // Dark mode variables are empty if they are identical to the light mode.
+        if ($prefix !== '' && ($value === null || $value === '')) {
+            $value = $style->getVariable($variableName, true);
+        }
+
+        return OklchColor::fromString($value ?? '') ?? $fallback;
+    }
+}
diff --git a/wcfsetup/install/files/lib/system/image/cover/photo/generator/OklchColor.class.php b/wcfsetup/install/files/lib/system/image/cover/photo/generator/OklchColor.class.php
new file mode 100644
index 00000000000..80f672b945c
--- /dev/null
+++ b/wcfsetup/install/files/lib/system/image/cover/photo/generator/OklchColor.class.php
@@ -0,0 +1,166 @@
+<?php
+
+namespace wcf\system\image\cover\photo\generator;
+
+/**
+ * Immutable color in the OKLCH color space, allows the hue and lightness to be
+ * shifted while keeping the perceived appearance of the color intact.
+ *
+ * @author      Marcel Werk
+ * @copyright   2001-2026 WoltLab GmbH
+ * @license     GNU Lesser General Public License <http://opensource.org/licenses/lgpl-license.php>
+ * @since       6.3
+ * @see         https://bottosson.github.io/posts/oklab/
+ */
+final class OklchColor
+{
+    public function __construct(
+        public readonly float $lightness,
+        public readonly float $chroma,
+        public readonly float $hue,
+    ) {}
+
+    /**
+     * Parses a color in the notation `#rgb`, `#rrggbb` or `rgb(a)(r, g, b[, a])`,
+     * the alpha channel is ignored.
+     */
+    public static function fromString(string $color): ?self
+    {
+        $color = \trim($color);
+
+        if (\preg_match('~^#([0-9a-f]{3}|[0-9a-f]{6})$~i', $color, $matches)) {
+            $hex = $matches[1];
+            if (\strlen($hex) === 3) {
+                $hex = $hex[0] . $hex[0] . $hex[1] . $hex[1] . $hex[2] . $hex[2];
+            }
+
+            return self::fromRgb(
+                \hexdec(\substr($hex, 0, 2)),
+                \hexdec(\substr($hex, 2, 2)),
+                \hexdec(\substr($hex, 4, 2)),
+            );
+        }
+
+        if (\preg_match('~^rgba?\(\s*(\d{1,3})\s*,\s*(\d{1,3})\s*,\s*(\d{1,3})\s*(?:,\s*[\d.]+\s*)?\)$~', $color, $matches)) {
+            return self::fromRgb((int)$matches[1], (int)$matches[2], (int)$matches[3]);
+        }
+
+        return null;
+    }
+
+    public static function fromRgb(int $red, int $green, int $blue): self
+    {
+        $r = self::toLinear($red / 255);
+        $g = self::toLinear($green / 255);
+        $b = self::toLinear($blue / 255);
+
+        $l = self::cbrt(0.4122214708 * $r + 0.5363325363 * $g + 0.0514459929 * $b);
+        $m = self::cbrt(0.2119034982 * $r + 0.6806995451 * $g + 0.1073969566 * $b);
+        $s = self::cbrt(0.0883024619 * $r + 0.2817188376 * $g + 0.6299787005 * $b);
+
+        $lightness = 0.2104542553 * $l + 0.7936177850 * $m - 0.0040720468 * $s;
+        $a = 1.9779984951 * $l - 2.4285922050 * $m + 0.4505937099 * $s;
+        $b = 0.0259040371 * $l + 0.7827717662 * $m - 0.8086757660 * $s;
+
+        return new self(
+            $lightness,
+            \sqrt($a * $a + $b * $b),
+            \fmod(\rad2deg(\atan2($b, $a)) + 360, 360),
+        );
+    }
+
+    public function withLightness(float $lightness): self
+    {
+        return new self(\max(0, \min(1, $lightness)), $this->chroma, $this->hue);
+    }
+
+    public function withChroma(float $chroma): self
+    {
+        return new self($this->lightness, \max(0, $chroma), $this->hue);
+    }
+
+    public function rotateHue(float $degrees): self
+    {
+        return new self($this->lightness, $this->chroma, \fmod($this->hue + $degrees + 360, 360));
+    }
+
+    /**
+     * Returns the color in the notation `#rrggbb`, colors outside of the sRGB
+     * gamut are mapped into it by reducing the chroma.
+     */
+    public function toHex(): string
+    {
+        $rgb = $this->toLinearRgb($this->chroma);
+        if (!self::isInGamut($rgb)) {
+            $low = 0;
+            $high = $this->chroma;
+            for ($i = 0; $i < 16; $i++) {
+                $chroma = ($low + $high) / 2;
+                if (self::isInGamut($this->toLinearRgb($chroma))) {
+                    $low = $chroma;
+                } else {
+                    $high = $chroma;
+                }
+            }
+
+            $rgb = $this->toLinearRgb($low);
+        }
+
+        return \sprintf(
+            '#%02x%02x%02x',
+            ...\array_map(
+                static fn(float $channel) => (int)\round(\max(0, \min(1, self::fromLinear($channel))) * 255),
+                $rgb
+            )
+        );
+    }
+
+    /**
+     * @return array{float, float, float}
+     */
+    private function toLinearRgb(float $chroma): array
+    {
+        $hue = \deg2rad($this->hue);
+        $a = $chroma * \cos($hue);
+        $b = $chroma * \sin($hue);
+
+        $l = ($this->lightness + 0.3963377774 * $a + 0.2158037573 * $b) ** 3;
+        $m = ($this->lightness - 0.1055613458 * $a - 0.0638541728 * $b) ** 3;
+        $s = ($this->lightness - 0.0894841775 * $a - 1.2914855480 * $b) ** 3;
+
+        return [
+            4.0767416621 * $l - 3.3077115913 * $m + 0.2309699292 * $s,
+            -1.2684380046 * $l + 2.6097574011 * $m - 0.3413193965 * $s,
+            -0.0041960863 * $l - 0.7034186147 * $m + 1.7076147010 * $s,
+        ];
+    }
+
+    /**
+     * @param array{float, float, float} $rgb
+     */
+    private static function isInGamut(array $rgb): bool
+    {
+        foreach ($rgb as $channel) {
+            if ($channel < -0.0001 || $channel > 1.0001) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    private static function toLinear(float $channel): float
+    {
+        return $channel <= 0.04045 ? $channel / 12.92 : (($channel + 0.055) / 1.055) ** 2.4;
+    }
+
+    private static function fromLinear(float $channel): float
+    {
+        return $channel <= 0.0031308 ? $channel * 12.92 : 1.055 * ($channel ** (1 / 2.4)) - 0.055;
+    }
+
+    private static function cbrt(float $value): float
+    {
+        return $value < 0 ? -((-$value) ** (1 / 3)) : $value ** (1 / 3);
+    }
+}

From 19cccf60c38bb10069fecc547972e741dbb50924 Mon Sep 17 00:00:00 2001
From: Marcel Werk <burntime@woltlab.com>
Date: Thu, 8 Oct 2026 15:41:44 +0200
Subject: [PATCH 2/2] Add option to choose between generated and style default
 cover photos

---
 com.woltlab.wcf/option.xml                          |  7 +++++++
 constants.php                                       |  1 +
 phpstan-ambient.neon                                |  1 +
 .../files/lib/data/user/UserProfile.class.php       | 13 +++++++++----
 .../cover/photo/GeneratedUserCoverPhoto.class.php   |  7 -------
 wcfsetup/install/lang/de.xml                        |  6 +++++-
 wcfsetup/install/lang/en.xml                        |  4 ++++
 7 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/com.woltlab.wcf/option.xml b/com.woltlab.wcf/option.xml
index c17dc84e241..2d7887f5191 100644
--- a/com.woltlab.wcf/option.xml
+++ b/com.woltlab.wcf/option.xml
@@ -1202,6 +1202,13 @@ silhouette:wcf.acp.option.avatar_default_type.silhouette</selectoptions>
 				<optiontype>boolean</optiontype>
 				<defaultvalue>1</defaultvalue>
 			</option>
+			<option name="user_cover_photo_default_type">
+				<categoryname>user.profile</categoryname>
+				<optiontype>select</optiontype>
+				<defaultvalue>generated</defaultvalue>
+				<selectoptions>generated:wcf.acp.option.user_cover_photo_default_type.generated
+style:wcf.acp.option.user_cover_photo_default_type.style</selectoptions>
+			</option>
 			<!-- /user.profile -->
 			<!-- user.list.members -->
 			<option name="members_list_users_per_page">
diff --git a/constants.php b/constants.php
index f74e1d76e04..9490e161879 100644
--- a/constants.php
+++ b/constants.php
@@ -179,6 +179,7 @@
 \define('OG_IMAGE', '');
 \define('HEAD_CODE', '');
 \define('AVATAR_DEFAULT_TYPE', 'initials');
+\define('USER_COVER_PHOTO_DEFAULT_TYPE', 'generated');
 \define('ARTICLE_ENABLE_VISIT_TRACKING', 1);
 \define('ENABLE_AD_ROTATION', 1);
 \define('ENABLE_POLLING', 1);
diff --git a/phpstan-ambient.neon b/phpstan-ambient.neon
index f2bd985b693..a4a8dc1cd0e 100644
--- a/phpstan-ambient.neon
+++ b/phpstan-ambient.neon
@@ -181,6 +181,7 @@ parameters:
         - OG_IMAGE
         - HEAD_CODE
         - AVATAR_DEFAULT_TYPE
+        - USER_COVER_PHOTO_DEFAULT_TYPE
         - ARTICLE_ENABLE_VISIT_TRACKING
         - ENABLE_AD_ROTATION
         - ENABLE_POLLING
diff --git a/wcfsetup/install/files/lib/data/user/UserProfile.class.php b/wcfsetup/install/files/lib/data/user/UserProfile.class.php
index 0b583d5dda7..a01895717f4 100644
--- a/wcfsetup/install/files/lib/data/user/UserProfile.class.php
+++ b/wcfsetup/install/files/lib/data/user/UserProfile.class.php
@@ -11,6 +11,7 @@
 use wcf\data\user\avatar\DefaultAvatar;
 use wcf\data\user\avatar\IUserAvatar;
 use wcf\data\user\avatar\StaticAvatar;
+use wcf\data\user\cover\photo\DefaultUserCoverPhoto;
 use wcf\data\user\cover\photo\GeneratedUserCoverPhoto;
 use wcf\data\user\cover\photo\IUserCoverPhoto;
 use wcf\data\user\cover\photo\UserCoverPhoto;
@@ -445,15 +446,19 @@ public function getCoverPhoto(bool $isACP = false)
     }
 
     /**
-     * Returns the cover photo that is shown if the user has no cover photo. Styles
-     * with a custom cover photo use it for all users, otherwise an individual
-     * cover photo is generated for each user.
+     * Returns the cover photo that is shown if the user has no cover photo. Depending
+     * on the option `USER_COVER_PHOTO_DEFAULT_TYPE`, this is either the cover photo of
+     * the style or an individual cover photo that is generated for each user.
      *
      * @since 6.3
      */
     public function getDefaultCoverPhoto(): IUserCoverPhoto
     {
-        return new GeneratedUserCoverPhoto($this->username);
+        if (\USER_COVER_PHOTO_DEFAULT_TYPE === 'generated') {
+            return new GeneratedUserCoverPhoto($this->username);
+        }
+
+        return new DefaultUserCoverPhoto();
     }
 
     /**
diff --git a/wcfsetup/install/files/lib/data/user/cover/photo/GeneratedUserCoverPhoto.class.php b/wcfsetup/install/files/lib/data/user/cover/photo/GeneratedUserCoverPhoto.class.php
index c546a0a9130..2e2ffed29d0 100644
--- a/wcfsetup/install/files/lib/data/user/cover/photo/GeneratedUserCoverPhoto.class.php
+++ b/wcfsetup/install/files/lib/data/user/cover/photo/GeneratedUserCoverPhoto.class.php
@@ -3,11 +3,9 @@
 namespace wcf\data\user\cover\photo;
 
 use wcf\system\image\cover\photo\generator\CoverPhotoGenerator;
-use wcf\system\style\StyleHandler;
 
 /**
  * Represents a default cover photo that is generated for each user individually.
- * Styles with a custom cover photo use it for all users instead.
  *
  * @author      Marcel Werk
  * @copyright   2001-2026 WoltLab GmbH
@@ -25,11 +23,6 @@ public function __construct(
     #[\Override]
     public function getURL(?bool $forceWebP = null): string
     {
-        // The style is resolved lazily to avoid side effects when only the object is needed.
-        if (StyleHandler::getInstance()->getStyle()->coverPhotoExtension !== '') {
-            return parent::getURL($forceWebP);
-        }
-
         if (!isset($this->url)) {
             $this->url = CoverPhotoGenerator::forActiveStyle()->getDataUri('user-' . \mb_strtolower($this->username));
         }
diff --git a/wcfsetup/install/lang/de.xml b/wcfsetup/install/lang/de.xml
index cbe7d690377..4e827adc6cd 100644
--- a/wcfsetup/install/lang/de.xml
+++ b/wcfsetup/install/lang/de.xml
@@ -1653,9 +1653,13 @@ Als Benachrichtigungs-URL in der Konfiguration der sofortigen Zahlungsbestätigu
 		<item name="wcf.acp.option.use_page_title_on_landing_page"><![CDATA[Titel der Seite als Überschrift auf Startseite anzeigen]]></item>
 		<item name="wcf.acp.option.head_code"><![CDATA[Head-Code]]></item>
 		<item name="wcf.acp.option.head_code.description"><![CDATA[Der hier angegebene Code wird im Head-Tag jeder Seite ausgegeben. Der Head-Code eignet sich z.B. sehr gut für die Einbindung von zusätzlichen Meta-Tags.]]></item>
-		<item name="wcf.acp.option.avatar_default_type"><![CDATA[Standard Avatar-Typ]]></item>
+		<item name="wcf.acp.option.avatar_default_type"><![CDATA[Standard-Avatar-Typ]]></item>
 		<item name="wcf.acp.option.avatar_default_type.initials"><![CDATA[Initialen]]></item>
 		<item name="wcf.acp.option.avatar_default_type.silhouette"><![CDATA[Silhouette]]></item>
+		<item name="wcf.acp.option.user_cover_photo_default_type"><![CDATA[Standard-Titelbild-Typ]]></item>
+		<item name="wcf.acp.option.user_cover_photo_default_type.description"><![CDATA[Generierte Titelbilder werden für jeden Benutzer individuell auf Basis der Farben des aktiven Stils erstellt und haben Vorrang vor dem Titelbild des Stils.]]></item>
+		<item name="wcf.acp.option.user_cover_photo_default_type.style"><![CDATA[Titelbild des Stils]]></item>
+		<item name="wcf.acp.option.user_cover_photo_default_type.generated"><![CDATA[Generiertes Titelbild je Benutzer]]></item>
 		<item name="wcf.acp.option.enable_ad_rotation"><![CDATA[Werbung abwechselnd anzeigen]]></item>
 		<item name="wcf.acp.option.enable_ad_rotation.description"><![CDATA[Sollte einer Position mehr als eine Werbung zugewiesen sein, so wird bei jedem Aufruf eine zufällige Werbung angezeigt. Bei Deaktivierung dieser Option werden alle Werbungen parallel angezeigt.]]></item>
 		<item name="wcf.acp.option.visitor_use_tiny_build"><![CDATA[Seitenbeschleunigung für Gäste aktivieren]]></item>
diff --git a/wcfsetup/install/lang/en.xml b/wcfsetup/install/lang/en.xml
index 0a75dbd975b..8d9afff6ce6 100644
--- a/wcfsetup/install/lang/en.xml
+++ b/wcfsetup/install/lang/en.xml
@@ -1639,6 +1639,10 @@ When prompted for the notification URL for the instant payment notifications, pl
 		<item name="wcf.acp.option.avatar_default_type"><![CDATA[Default Avatar Type]]></item>
 		<item name="wcf.acp.option.avatar_default_type.initials"><![CDATA[Initials]]></item>
 		<item name="wcf.acp.option.avatar_default_type.silhouette"><![CDATA[Silhouette]]></item>
+		<item name="wcf.acp.option.user_cover_photo_default_type"><![CDATA[Default Cover Photo Type]]></item>
+		<item name="wcf.acp.option.user_cover_photo_default_type.description"><![CDATA[Generated cover photos are created individually for each user based on the colors of the active style and take precedence over the cover photo of the style.]]></item>
+		<item name="wcf.acp.option.user_cover_photo_default_type.style"><![CDATA[Cover photo of the style]]></item>
+		<item name="wcf.acp.option.user_cover_photo_default_type.generated"><![CDATA[Generated cover photo per user]]></item>
 		<item name="wcf.acp.option.enable_ad_rotation"><![CDATA[Enable ad rotation]]></item>
 		<item name="wcf.acp.option.enable_ad_rotation.description"><![CDATA[If there is more than one ad per placeholder, a random ad will be displayed every time. Disabling this option will display all ads simultaneously.]]></item>
 		<item name="wcf.acp.option.visitor_use_tiny_build"><![CDATA[Enable accelerated guest view]]></item>