Mario Breskic

Kommunikationsdesigner

Schlagwort: snippets

  • How to retire a ghost ActivityPub account left behind by WordPress and move it to Mastodon

    The ActivityPub plugin for WordPress can turn your website, your WordPress user account, or both into actors in the Fediverse.

    If you later uninstall the plugin, those actors do not necessarily disappear from remote Mastodon servers. Other servers may continue to remember them, search for them, display them, or send requests to inbox URLs that no longer exist.

    This can leave you with what looks like a ghost account:

    @yourname@www.example.com

    while your actual Mastodon account is:

    @yourname@mastodon.example

    Simply uninstalling ActivityPub does not tell the rest of the Fediverse that the old actor has moved. Returning a generic 404 Not Found does not help either.

    The proper repair is:

    1. temporarily restore the old WordPress actor;
    2. add it as an alias of the real Mastodon account;
    3. send a signed ActivityPub Move;
    4. preserve the retired actor and its movedTo property;
    5. close its old inbox with 410 Gone;
    6. remove the full ActivityPub plugin without erasing the migration record.

    This tutorial walks through that entire procedure on a Plesk server using WP Toolkit and WP-CLI.

    Disclosure

    This tutorial was made with ChatGPT.

    ChatGPT and I successfully implemented and verified this migration on my own WordPress website and Mastodon server. I executed every command, inspected the responses, verified the database records, removed the ActivityPub plugin, and tested the final retired actors and inboxes.

    The tested environment was:

    Plesk Obsidian
WordPress 7.0
ActivityPub for WordPress 9.0.1
PHP 8.2
Mastodon 4.6.0
Ubuntu Linux

    Plugin interfaces and internal paths may change in later versions. Read each command before running it and keep a complete website and database backup.

    What this procedure does

    The procedure creates a proper ActivityPub migration from an old WordPress actor to a real Mastodon actor.

    The old actor will publish:

    {
  "movedTo": "https://mastodon.example/users/alice"
}

    Its outbox will contain a Move activity resembling:

    {
  "type": "Move",
  "object": "https://www.example.com/?author=1",
  "target": "https://mastodon.example/users/alice"
}

    The new Mastodon actor must reciprocally list the old actor under:

    {
  "alsoKnownAs": [
    "https://www.example.com/?author=1"
  ]
}

    This reciprocal relationship prevents one account from falsely claiming that it moved to an unrelated person.

    What it does not do

    This procedure does not:

    • copy old WordPress posts into Mastodon;
    • guarantee immediate deletion from every remote server;
    • force every Fediverse implementation to refresh its cache immediately;
    • forward old inbox traffic into Mastodon;
    • turn an HTTP redirect into an account migration.

    The old actor remains a small, machine-readable retirement notice.

    Why forwarding the old inbox is the wrong solution

    Suppose remote servers are still sending requests to:

    https://www.example.com/wp-json/activitypub/1.0/actors/0/inbox

    It may seem reasonable to proxy those requests to:

    https://mastodon.example/users/alice/inbox

    Do not do this.

    ActivityPub deliveries are signed for a particular host, request target and actor identity. Rewriting the destination does not transform an activity addressed to one actor into an activity addressed to another actor.

    A reverse proxy relocates an HTTP request. It does not transfer an ActivityPub identity.

    The correct mechanism is a Move activity.

    Before beginning

    You need:

    • SSH root access to the Plesk server;
    • access to the WordPress administration interface;
    • access to the destination Mastodon account;
    • Plesk WP Toolkit;
    • the ActivityPub plugin temporarily installed and active;
    • curl;
    • Python 3;
    • a current website and database backup.

    jq is not required. All JSON examples in this tutorial use Python.

    Part 1: define your installation values

    Begin by listing the WordPress installations known to Plesk:

    plesk ext wp-toolkit --list

    Example:

    ID  Installation Path  Website URL
8   /httpdocs          https://www.example.com

    Set the values for your installation:

    WP_INSTANCE_ID='8'

VHOST='/var/www/vhosts/example.com'
DOCROOT="$VHOST/httpdocs"

SITE_HOST='www.example.com'

TARGET_HANDLE='alice@mastodon.example'
TARGET_ACTOR='https://mastodon.example/users/alice'

PHP_BIN='/opt/plesk/php/8.2/bin/php'

    Replace every example value with the real value for your server.

    Do not guess the destination actor URL. Mastodon actor URLs normally resemble:

    https://mastodon.example/users/alice

    They are not necessarily the same as the human profile URL:

    https://mastodon.example/@alice

    Part 2: restore the ActivityPub plugin temporarily

    If ActivityPub is still installed but inactive:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- \
  plugin activate activitypub

    If it was deleted:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- \
  plugin install activitypub --activate

    Check the installed version:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- \
  plugin get activitypub \
  --fields=name,status,version \
  --format=table

    Example:

    Field    Value
name     activitypub
version  9.0.1
status   active

    Do not remove the plugin again until the migration, export and retirement handler have all been verified.

    Part 3: identify every old WordPress actor

    A WordPress installation may expose more than one ActivityPub actor.

    This was the crucial detail in my case.

    I had:

    @mario@www.mariobreskic.de

    which resolved to:

    https://www.mariobreskic.de/?author=1

    and a separate site-wide blog actor:

    @mariobreskic.de@www.mariobreskic.de

    which resolved to:

    https://www.mariobreskic.de/?author=0

    They had separate inboxes:

    /wp-json/activitypub/1.0/actors/1/inbox
/wp-json/activitypub/1.0/actors/0/inbox

    A request to /actors/0/inbox therefore did not belong to the same actor as /actors/1/inbox.

    3.1 Check the user actor with WebFinger

    Replace the handle:

    curl -fsS -G \
  -H 'Accept: application/jrd+json' \
  --data-urlencode \
  'resource=acct:alice@www.example.com' \
  'https://www.example.com/.well-known/webfinger' |
python3 -m json.tool

    Look for:

    {
  "rel": "self",
  "type": "application/activity+json",
  "href": "https://www.example.com/?author=1"
}

    The href value is the canonical ActivityPub actor ID.

    It is not the inbox URL.

    3.2 Check for a site-wide blog actor

    The blog actor may have a handle based on the website domain:

    curl -fsS -G \
  -H 'Accept: application/jrd+json' \
  --data-urlencode \
  'resource=acct:example.com@www.example.com' \
  'https://www.example.com/.well-known/webfinger' |
python3 -m json.tool

    A blog actor may resolve to:

    https://www.example.com/?author=0

    and may use the ActivityPub type:

    Group

    rather than:

    Person

    That is normal.

    3.3 If the blog actor cannot be found

    Open the WordPress administration interface and locate the ActivityPub profile settings.

    Enable the blog-wide or site-wide profile temporarily.

    Its identifier must match the old identifier used when the account was originally federated.

    Then save the WordPress permalink settings once:

    Settings
→ Permalinks
→ Save Changes

    Do not change the permalink structure. Saving it refreshes WordPress rewrite rules.

    Repeat the WebFinger request afterwards.

    Part 4: inspect each actor

    Inspect the user actor:

    curl -fsS \
  -H 'Accept: application/activity+json' \
  'https://www.example.com/?author=1' |
python3 -c '
import json
import sys

data = json.load(sys.stdin)

for key in (
    "id",
    "type",
    "preferredUsername",
    "inbox",
    "outbox",
    "followers",
    "alsoKnownAs",
    "movedTo",
):
    print(f"{key}: {data.get(key)}")
'

    Inspect the blog actor:

    curl -fsS \
  -H 'Accept: application/activity+json' \
  'https://www.example.com/?author=0' |
python3 -c '
import json
import sys

data = json.load(sys.stdin)

for key in (
    "id",
    "type",
    "preferredUsername",
    "inbox",
    "outbox",
    "followers",
    "alsoKnownAs",
    "movedTo",
):
    print(f"{key}: {data.get(key)}")
'

    Record the exact id value of every actor.

    For the remaining examples, assume:

    OLD_ACTOR_0='https://www.example.com/?author=0'
OLD_HANDLE_0='example.com@www.example.com'

OLD_ACTOR_1='https://www.example.com/?author=1'
OLD_HANDLE_1='alice@www.example.com'

    Remove actor 0 or actor 1 from the procedure if your site only has one of them.

    Part 5: add the old actors as aliases in Mastodon

    Log in to the destination Mastodon account.

    Open:

    Preferences
→ Account
→ Moving from a different account
→ Create account alias

    Add the old handle:

    alice@www.example.com

    If the blog actor exists, add it separately:

    example.com@www.example.com

    Do not include a leading @ unless the interface specifically requests it.

    Adding an alias does not move anything by itself. It tells Mastodon that the destination account consents to being the target of a later migration.

    5.1 If Mastodon cannot find the old account

    Do not continue.

    Confirm that WebFinger works:

    curl -fsS -G \
  -H 'Accept: application/jrd+json' \
  --data-urlencode \
  'resource=acct:example.com@www.example.com' \
  'https://www.example.com/.well-known/webfinger' |
python3 -m json.tool

    Also try searching inside Mastodon for:

    @example.com@www.example.com

    or for the direct actor URL:

    https://www.example.com/?author=0

    Once Mastodon can resolve the actor, retry the alias form.

    Part 6: verify the aliases on the destination actor

    The destination Mastodon actor must publish every old actor URL under alsoKnownAs.

    Run:

    curl -fsS \
  -H 'Accept: application/activity+json' \
  "$TARGET_ACTOR" |
python3 -c '
import json
import sys

data = json.load(sys.stdin)

print("id:", data.get("id"))
print("alsoKnownAs:")

for value in data.get("alsoKnownAs", []):
    print("  " + value)
'

    Required result:

    https://www.example.com/?author=0
https://www.example.com/?author=1

    Do not run the Move command for an actor whose URL is absent.

    Part 7: check whether WordPress retained followers

    For actor 1:

    curl -fsS \
  -H 'Accept: application/activity+json' \
  'https://www.example.com/wp-json/activitypub/1.0/actors/1/followers' |
python3 -c '
import json
import sys

data = json.load(sys.stdin)
print("type:", data.get("type"))
print("totalItems:", data.get("totalItems"))
'

    For actor 0:

    curl -fsS \
  -H 'Accept: application/activity+json' \
  'https://www.example.com/wp-json/activitypub/1.0/actors/0/followers' |
python3 -c '
import json
import sys

data = json.load(sys.stdin)
print("type:", data.get("type"))
print("totalItems:", data.get("totalItems"))
'

    A result such as:

    totalItems: 0

    does not prevent the migration.

    It means WordPress has no locally stored follower inboxes to notify directly. The old actor can still publish movedTo, and remote servers can discover it when they refresh the actor.

    Part 8: run ActivityPub commands correctly through Plesk

    Plesk integrates WP-CLI through WP Toolkit.

    Test the ActivityPub Move command:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- \
  activitypub move --help \
  --skip-plugins=false

    The final option is important:

    --skip-plugins=false

    Without it, Plesk may run WP-CLI without loading ordinary WordPress plugins. The result will be:

    Error: 'activitypub' is not a registered wp command.

    The plugin can be active in WordPress while still being absent from the WP-CLI runtime.

    Part 9: move the user actor

    Run:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- \
  activitypub move \
  'https://www.example.com/?author=1' \
  "$TARGET_ACTOR" \
  --skip-plugins=false

    Expected result:

    Success: Move Scheduled.

    Do not repeat the command after it succeeds.

    Part 10: move the blog actor

    Run:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- \
  activitypub move \
  'https://www.example.com/?author=0' \
  "$TARGET_ACTOR" \
  --skip-plugins=false

    Expected:

    Success: Move Scheduled.

    Again, do not repeat it after success.

    Troubleshooting: “Invalid target” or “Ungültiges Ziel”

    This means WordPress fetched the destination actor but did not find the old actor URL under alsoKnownAs.

    First verify the destination actor again:

    curl -fsS \
  -H 'Accept: application/activity+json' \
  "$TARGET_ACTOR" |
python3 -m json.tool

    If the alias is present publicly, WordPress may have cached an older copy.

    Generate the plugin’s cache key:

    CACHE_KEY=$(
  python3 - "$TARGET_ACTOR" <<'PY'
import hashlib
import sys

url = sys.argv[1]
print("activitypub_http_" + hashlib.md5(url.encode()).hexdigest())
PY
)

    Display it:

    echo "$CACHE_KEY"

    Delete the transient:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- \
  transient delete "$CACHE_KEY"

    Then inspect what WordPress fetches without cache:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- eval '
$url = "https://mastodon.example/users/alice";

$data = \Activitypub\Http::get_remote_object($url, false);

if (is_wp_error($data)) {
    WP_CLI::error(
        $data->get_error_code() . ": " .
        $data->get_error_message()
    );
}

echo "id: " . ($data["id"] ?? "MISSING") . PHP_EOL;
echo "alsoKnownAs:" . PHP_EOL;

foreach (($data["alsoKnownAs"] ?? array()) as $alias) {
    echo "  " . $alias . PHP_EOL;
}
' --skip-plugins=false

    Replace the target URL inside the PHP code.

    After the correct alias appears, run the Move command once more.

    Important warning for ActivityPub 9.0.1

    Do not experiment with incorrect destination URLs.

    In version 9.0.1, the plugin writes the movedTo setting before it completes target validation. Verify the destination and its aliases before running the command.

    Part 11: verify the public actors

    Check both:

    for NUMBER in 0 1; do
  echo "=== actor $NUMBER ==="

  curl -fsS \
    -H 'Accept: application/activity+json' \
    "https://www.example.com/?author=$NUMBER" |
  python3 -c '
import json
import sys

data = json.load(sys.stdin)

print("id:", data.get("id"))
print("type:", data.get("type"))
print("movedTo:", data.get("movedTo"))
'

  echo
done

    Expected:

    === actor 0 ===
id: https://www.example.com/?author=0
type: Group
movedTo: https://mastodon.example/users/alice

=== actor 1 ===
id: https://www.example.com/?author=1
type: Person
movedTo: https://mastodon.example/users/alice

    Part 12: verify the Move activities in the database

    The public outbox REST page may be paginated or may not show the newest Move where you expect it.

    Query the WordPress outbox records directly:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- eval '
$posts = get_posts(
    array(
        "post_type"      => "ap_outbox",
        "post_status"    => "any",
        "posts_per_page" => 100,
        "orderby"        => "ID",
        "order"          => "DESC",
    )
);

foreach ($posts as $post) {
    $data = json_decode($post->post_content, true);

    if (($data["type"] ?? "") !== "Move") {
        continue;
    }

    echo "ID: " . $post->ID . PHP_EOL;
    echo "type: " . ($data["type"] ?? "MISSING") . PHP_EOL;
    echo "object: " . ($data["object"] ?? "MISSING") . PHP_EOL;
    echo "target: " . ($data["target"] ?? "MISSING") . PHP_EOL;
    echo PHP_EOL;
}
' --skip-plugins=false

    You need one Move for every retired actor:

    object: https://www.example.com/?author=0
target: https://mastodon.example/users/alice

    and:

    object: https://www.example.com/?author=1
target: https://mastodon.example/users/alice

    Part 13: archive the final actor state

    Do not uninstall ActivityPub yet.

    Create an archive outside the public document root:

    ARCHIVE="$VHOST/private/activitypub-retired"

SITE_USER=$(stat -c '%U' "$DOCROOT/wp-config.php")
SITE_GROUP=$(stat -c '%G' "$DOCROOT/wp-config.php")

install -d \
  -o "$SITE_USER" \
  -g "$SITE_GROUP" \
  -m 0750 \
  "$ARCHIVE"

    13.1 Save the actor documents

    curl -fsS \
  -H 'Accept: application/activity+json' \
  'https://www.example.com/?author=0' \
  -o "$ARCHIVE/actor-0.json"

curl -fsS \
  -H 'Accept: application/activity+json' \
  'https://www.example.com/?author=1' \
  -o "$ARCHIVE/actor-1.json"

    13.2 Save the WebFinger documents

    curl -fsS -G \
  -H 'Accept: application/jrd+json' \
  --data-urlencode \
  'resource=acct:example.com@www.example.com' \
  'https://www.example.com/.well-known/webfinger' \
  -o "$ARCHIVE/webfinger-0.json"

curl -fsS -G \
  -H 'Accept: application/jrd+json' \
  --data-urlencode \
  'resource=acct:alice@www.example.com' \
  'https://www.example.com/.well-known/webfinger' \
  -o "$ARCHIVE/webfinger-1.json"

    13.3 Export the Move activities

    Edit the two actor URLs inside this command:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- eval '
$actors = array(
    "0" => "https://www.example.com/?author=0",
    "1" => "https://www.example.com/?author=1",
);

$directory =
    "/var/www/vhosts/example.com/private/activitypub-retired";

$posts = get_posts(
    array(
        "post_type"      => "ap_outbox",
        "post_status"    => "any",
        "posts_per_page" => 100,
        "orderby"        => "ID",
        "order"          => "DESC",
    )
);

$found = array();

foreach ($posts as $post) {
    $data = json_decode($post->post_content, true);

    if (
        !is_array($data) ||
        ($data["type"] ?? "") !== "Move"
    ) {
        continue;
    }

    foreach ($actors as $number => $actor_url) {
        if (
            !isset($found[$number]) &&
            ($data["object"] ?? "") === $actor_url
        ) {
            $filename =
                $directory . "/move-" . $number . ".json";

            $json = wp_json_encode(
                $data,
                JSON_PRETTY_PRINT |
                JSON_UNESCAPED_SLASHES |
                JSON_UNESCAPED_UNICODE
            );

            if (
                false === file_put_contents(
                    $filename,
                    $json . PHP_EOL
                )
            ) {
                WP_CLI::error(
                    "Could not write " . $filename
                );
            }

            $found[$number] = $post->ID;
        }
    }
}

foreach ($actors as $number => $actor_url) {
    if (!isset($found[$number])) {
        WP_CLI::error(
            "No Move activity found for actor " . $number
        );
    }
}

foreach ($found as $number => $post_id) {
    echo "actor " . $number .
        ": outbox post " . $post_id .
        PHP_EOL;
}
' --skip-plugins=false

    Correct the archive directory in the PHP code before running it.

    13.4 Set permissions

    chown "$SITE_USER:$SITE_GROUP" "$ARCHIVE"/*.json
chmod 0640 "$ARCHIVE"/*.json

ls -la "$ARCHIVE"

    Expected files:

    actor-0.json
actor-1.json
move-0.json
move-1.json
webfinger-0.json
webfinger-1.json

    Part 14: validate the archive

    python3 - <<'PY'
import json
from pathlib import Path

base = Path(
    "/var/www/vhosts/example.com/private/activitypub-retired"
)

target = "https://mastodon.example/users/alice"

for number in ("0", "1"):
    with (
        base / f"actor-{number}.json"
    ).open(encoding="utf-8") as file:
        actor = json.load(file)

    with (
        base / f"webfinger-{number}.json"
    ).open(encoding="utf-8") as file:
        webfinger = json.load(file)

    with (
        base / f"move-{number}.json"
    ).open(encoding="utf-8") as file:
        move = json.load(file)

    self_links = [
        link.get("href")
        for link in webfinger.get("links", [])
        if link.get("rel") == "self"
    ]

    print(f"=== actor {number} ===")
    print("actor id:", actor.get("id"))
    print("actor type:", actor.get("type"))
    print("movedTo:", actor.get("movedTo"))
    print("WebFinger self:", self_links)
    print("Move type:", move.get("type"))
    print("Move object:", move.get("object"))
    print("Move target:", move.get("target"))

    assert actor.get("movedTo") == target
    assert move.get("type") == "Move"
    assert move.get("object") == actor.get("id")
    assert move.get("target") == target
    assert actor.get("id") in self_links

    print("VALID")
    print()

print("All retirement records are valid.")
PY

    Edit the archive path and target actor before running it.

    Do not continue unless every actor prints:

    VALID

    Part 15: install a permanent retirement handler

    The full ActivityPub plugin is no longer needed after the migration, but the old identities should remain resolvable.

    We will install a small must-use WordPress plugin.

    It will:

    • serve the archived WebFinger responses;
    • serve the archived actor documents;
    • serve the archived Move objects;
    • return 410 Gone from the old inboxes;
    • leave ordinary HTML author pages untouched.

    Create the file:

    cat > /tmp/activitypub-retirement.php <<'PHP'
<?php
/**
 * Plugin Name: Retired ActivityPub Identities
 * Description: Preserves moved ActivityPub actors after removing the ActivityPub plugin.
 * Version: 1.0.0
 */

defined( 'ABSPATH' ) || exit;

/*
 * CHANGE THESE VALUES.
 */
const MB_AP_RETIREMENT_ARCHIVE =
	'/var/www/vhosts/example.com/private/activitypub-retired';

const MB_AP_RETIREMENT_ORIGIN =
	'https://www.example.com';

const MB_AP_RETIREMENT_TARGET =
	'https://mastodon.example/users/alice';


function mb_ap_retirement_send_file(
	string $filename,
	string $content_type
): void {
	$path = MB_AP_RETIREMENT_ARCHIVE . '/' . $filename;

	if ( ! is_readable( $path ) ) {
		status_header( 500 );
		header( 'Content-Type: application/json; charset=utf-8' );
		header( 'Cache-Control: no-store' );

		echo wp_json_encode(
			array(
				'error'   => 'Retirement archive unavailable',
				'missing' => $filename,
			)
		);

		exit;
	}

	status_header( 200 );

	header(
		'Content-Type: ' .
		$content_type .
		'; charset=utf-8'
	);

	header( 'Cache-Control: public, max-age=3600' );
	header( 'X-Content-Type-Options: nosniff' );
	header( 'Vary: Accept' );
	header( 'Content-Length: ' . filesize( $path ) );

	if (
		'HEAD' !== strtoupper(
			$_SERVER['REQUEST_METHOD'] ?? 'GET'
		)
	) {
		readfile( $path );
	}

	exit;
}


function mb_ap_retirement_send_gone(): void {
	$body = wp_json_encode(
		array(
			'error'   => 'Gone',
			'message' => 'This ActivityPub actor has moved.',
			'movedTo' => MB_AP_RETIREMENT_TARGET,
		),
		JSON_UNESCAPED_SLASHES
	);

	status_header( 410 );

	header(
		'Content-Type: application/activity+json; charset=utf-8'
	);

	header( 'Cache-Control: no-store' );
	header( 'X-Content-Type-Options: nosniff' );

	if (
		'HEAD' !== strtoupper(
			$_SERVER['REQUEST_METHOD'] ?? 'GET'
		)
	) {
		echo $body;
	}

	exit;
}


function mb_ap_retirement_accepts_activitypub(): bool {
	$accept = strtolower(
		$_SERVER['HTTP_ACCEPT'] ?? ''
	);

	return str_contains(
		$accept,
		'application/activity+json'
	) || str_contains(
		$accept,
		'application/ld+json'
	);
}


add_action(
	'parse_request',
	static function (): void {
		$request_uri =
			$_SERVER['REQUEST_URI'] ?? '/';

		$path = parse_url(
			$request_uri,
			PHP_URL_PATH
		);

		$method = strtoupper(
			$_SERVER['REQUEST_METHOD'] ?? 'GET'
		);

		/*
		 * CHANGE THE TWO acct: VALUES.
		 */
		if (
			'/.well-known/webfinger' === rtrim(
				(string) $path,
				'/'
			)
			&& in_array(
				$method,
				array( 'GET', 'HEAD' ),
				true
			)
		) {
			$resource = isset( $_GET['resource'] )
				? trim(
					wp_unslash(
						$_GET['resource']
					)
				)
				: '';

			$webfinger_files = array(
				'acct:example.com@www.example.com'
					=> 'webfinger-0.json',

				'acct:alice@www.example.com'
					=> 'webfinger-1.json',
			);

			if (
				isset(
					$webfinger_files[ $resource ]
				)
			) {
				mb_ap_retirement_send_file(
					$webfinger_files[ $resource ],
					'application/jrd+json'
				);
			}

			return;
		}

		/*
		 * Serve the retired actors only when an
		 * ActivityPub representation is requested.
		 */
		if (
			'/' === $path
			&& in_array(
				$method,
				array( 'GET', 'HEAD' ),
				true
			)
			&& mb_ap_retirement_accepts_activitypub()
		) {
			$author = isset( $_GET['author'] )
				? (string) wp_unslash(
					$_GET['author']
				)
				: '';

			$actor_files = array(
				'0' => 'actor-0.json',
				'1' => 'actor-1.json',
			);

			if ( isset( $actor_files[ $author ] ) ) {
				mb_ap_retirement_send_file(
					$actor_files[ $author ],
					'application/activity+json'
				);
			}
		}

		/*
		 * Preserve dereferenceable Move activity IDs.
		 */
		if (
			in_array(
				$method,
				array( 'GET', 'HEAD' ),
				true
			)
			&& mb_ap_retirement_accepts_activitypub()
		) {
			$current_url =
				MB_AP_RETIREMENT_ORIGIN .
				$request_uri;

			foreach (
				array( '0', '1' ) as $number
			) {
				$filename =
					'move-' .
					$number .
					'.json';

				$file =
					MB_AP_RETIREMENT_ARCHIVE .
					'/' .
					$filename;

				if ( ! is_readable( $file ) ) {
					continue;
				}

				$move = json_decode(
					file_get_contents( $file ),
					true
				);

				if (
					is_array( $move )
					&& isset( $move['id'] )
					&& $move['id'] === $current_url
				) {
					mb_ap_retirement_send_file(
						$filename,
						'application/activity+json'
					);
				}
			}
		}

		/*
		 * Retire old inboxes and collections.
		 */
		$normalised_path =
			rtrim( (string) $path, '/' );

		$is_retired_endpoint =
			'/wp-json/activitypub/1.0/inbox'
				=== $normalised_path
			|| preg_match(
				'#^/wp-json/activitypub/1\.0/' .
				'actors/[01]/' .
				'(?:inbox|outbox(?:/stream)?|' .
				'followers|following|liked|' .
				'collections(?:/.*)?)$#',
				$normalised_path
			);

		if ( $is_retired_endpoint ) {
			mb_ap_retirement_send_gone();
		}
	},
	-1000
);
PHP

    Edit these values before installing:

    MB_AP_RETIREMENT_ARCHIVE
MB_AP_RETIREMENT_ORIGIN
MB_AP_RETIREMENT_TARGET
the two WebFinger acct: identifiers

    If you only have one retired actor, remove the unused map entries and files.

    15.1 Check the syntax

    "$PHP_BIN" -l /tmp/activitypub-retirement.php

    Required:

    No syntax errors detected

    15.2 Install it as a must-use plugin

    MUPLUGINS="$DOCROOT/wp-content/mu-plugins"

install -d \
  -o "$SITE_USER" \
  -g "$SITE_GROUP" \
  -m 0755 \
  "$MUPLUGINS"

install \
  -o "$SITE_USER" \
  -g "$SITE_GROUP" \
  -m 0644 \
  /tmp/activitypub-retirement.php \
  "$MUPLUGINS/activitypub-retirement.php"

    Confirm:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- \
  plugin list \
  --status=must-use \
  --fields=name,status,version \
  --format=table

    Expected:

    activitypub-retirement  must-use  1.0.0

    Part 16: test the retirement handler before removing ActivityPub

    16.1 Test WebFinger

    for RESOURCE in \
  'acct:example.com@www.example.com' \
  'acct:alice@www.example.com'
do
  echo "=== $RESOURCE ==="

  curl -fsS -G \
    -H 'Accept: application/jrd+json' \
    --data-urlencode "resource=$RESOURCE" \
    'https://www.example.com/.well-known/webfinger' |
  python3 -c '
import json
import sys

data = json.load(sys.stdin)

print("subject:", data.get("subject"))

for link in data.get("links", []):
    if link.get("rel") == "self":
        print("self:", link.get("href"))
'

  echo
done

    16.2 Test both actors

    for NUMBER in 0 1; do
  echo "=== actor $NUMBER ==="

  curl -fsS \
    -H 'Accept: application/activity+json' \
    "https://www.example.com/?author=$NUMBER" |
  python3 -c '
import json
import sys

data = json.load(sys.stdin)

print("id:", data.get("id"))
print("type:", data.get("type"))
print("movedTo:", data.get("movedTo"))
'

  echo
done

    16.3 Confirm normal HTML remains available

    for NUMBER in 0 1; do
  curl -sS \
    -o /dev/null \
    -H 'Accept: text/html' \
    -w "author=$NUMBER: HTTP %{http_code}, %{content_type}\n" \
    "https://www.example.com/?author=$NUMBER"
done

    A 200 or normal WordPress 301 redirect is acceptable.

    16.4 Test the retired inboxes

    for NUMBER in 0 1; do
  curl -sS \
    -o /dev/null \
    -X POST \
    -H 'Content-Type: application/activity+json' \
    -d '{}' \
    -w "actor $NUMBER inbox: HTTP %{http_code}\n" \
    "https://www.example.com/wp-json/activitypub/1.0/actors/$NUMBER/inbox"
done

    Required:

    HTTP 410

    Test the shared inbox:

    curl -sS \
  -o /dev/null \
  -X POST \
  -H 'Content-Type: application/activity+json' \
  -d '{}' \
  -w "shared inbox: HTTP %{http_code}\n" \
  'https://www.example.com/wp-json/activitypub/1.0/inbox'

    Required:

    HTTP 410

    Part 17: deactivate ActivityPub

    Do not delete it immediately.

    Deactivate it first:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- \
  plugin deactivate activitypub \
  --skip-plugins=false

    Confirm:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- \
  plugin get activitypub \
  --fields=name,status,version \
  --format=table

    Status must be:

    inactive

    Repeat all tests from Part 16.

    The WebFinger documents, actor documents and 410 Gone inboxes must continue working with the main ActivityPub plugin inactive.

    Part 18: delete the ActivityPub plugin files

    Only after every test succeeds:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- \
  plugin delete activitypub

    The retirement MU-plugin is separate and will remain installed.

    Confirm:

    plesk ext wp-toolkit --wp-cli -instance-id "$WP_INSTANCE_ID" -- \
  plugin list \
  --fields=name,status,version \
  --format=table |
grep -E '^(name|activitypub)'

    Only the table header should remain.

    Part 19: final verification

    Use a saved response body rather than piping directly into Python. This produces clearer diagnostics if a proxy cache briefly returns an empty response.

    for NUMBER in 0 1; do
  BODY="/tmp/retired-actor-$NUMBER.json"

  echo "=== actor $NUMBER ==="

  curl --fail-with-body -sS \
    -H 'Accept: application/activity+json' \
    -H 'Cache-Control: no-cache' \
    "https://www.example.com/?author=$NUMBER" \
    -o "$BODY"

  python3 -c '
import json
import sys

with open(sys.argv[1], encoding="utf-8") as file:
    data = json.load(file)

print("id:", data.get("id"))
print("type:", data.get("type"))
print("movedTo:", data.get("movedTo"))
' "$BODY"

  curl -sS \
    -o /dev/null \
    -X POST \
    -H 'Content-Type: application/activity+json' \
    -d '{}' \
    -w "inbox: HTTP %{http_code}\n" \
    "https://www.example.com/wp-json/activitypub/1.0/actors/$NUMBER/inbox"

  echo
done

    Final expected state:

    actor 0:
type: Group
movedTo: real Mastodon actor
inbox: HTTP 410

actor 1:
type: Person
movedTo: real Mastodon actor
inbox: HTTP 410

    Check both WebFinger identities once more:

    for RESOURCE in \
  'acct:example.com@www.example.com' \
  'acct:alice@www.example.com'
do
  curl --fail-with-body -sS -G \
    -H 'Accept: application/jrd+json' \
    -H 'Cache-Control: no-cache' \
    --data-urlencode "resource=$RESOURCE" \
    'https://www.example.com/.well-known/webfinger' |
  python3 -c '
import json
import sys

data = json.load(sys.stdin)

print("subject:", data.get("subject"))

for link in data.get("links", []):
    if link.get("rel") == "self":
        print("self:", link.get("href"))
'
done

    Common errors

    /usr/bin/env: php: No such file or directory

    Plesk may not expose a generic php binary in the shell path.

    Use the Plesk WP Toolkit wrapper:

    plesk ext wp-toolkit --wp-cli -instance-id 8 -- ...

    or invoke the configured Plesk PHP binary directly:

    /opt/plesk/php/8.2/bin/php

    Do not create a global PHP symlink merely to satisfy WP-CLI.

    'activitypub' is not a registered wp command

    Add:

    --skip-plugins=false

    to the WP Toolkit command.

    Mastodon cannot find the old account

    The actor is not currently discoverable through WebFinger.

    Temporarily re-enable the relevant ActivityPub profile in WordPress, save the permalink settings and verify:

    /.well-known/webfinger?resource=acct:username@domain

    before retrying the Mastodon alias.

    The follower count is zero

    This is not a migration failure.

    It means WordPress has no stored followers to notify directly. The actor can still publish movedTo, and remote servers can discover it later.

    The REST outbox does not display the Move

    Query the ap_outbox records directly with WP-CLI. Pagination and filtering can make the public outbox misleading.

    Python reports JSONDecodeError

    Save the HTTP body and headers first:

    curl -sS \
  -D /tmp/headers.txt \
  -o /tmp/body.json \
  -H 'Accept: application/activity+json' \
  'https://www.example.com/?author=0'

    Inspect:

    cat /tmp/headers.txt
wc -c /tmp/body.json
python3 -m json.tool /tmp/body.json

    A transient empty response during cache turnover does not necessarily mean the retirement handler is broken.

    Remote servers continue posting to the old inbox

    They may retain stale actor information for some time.

    The correct final response is:

    410 Gone

    Do not proxy those requests into Mastodon.

    What must remain permanently

    Keep these files:

    wp-content/mu-plugins/activitypub-retirement.php

    and:

    /private/activitypub-retired/

    Back them up with the rest of the website.

    Also retain the old account aliases on the destination Mastodon account. They are part of the reciprocal evidence that validates the Move.

    The final architecture is deliberately small:

    Old WordPress actor
    ↓
movedTo
    ↓
Real Mastodon actor

    The old actor remains readable, but inert.

    Its inbox is closed.

    Its identity is not forwarded, impersonated or silently discarded.

    The Fediverse receives an explicit statement: this actor existed, and it moved here.

    The protocol requirements were checked against Mastodon’s official documentation for Move, alsoKnownAs, account aliases and WebFinger. The WordPress commands and migration behavior were checked against ActivityPub for WordPress 9.0.1 source code, including its external-move implementation, cache key and CLI registration. The Plesk command form and plugin deactivation/deletion steps were checked against the official Plesk and WP-CLI documentation.

  • BlackInk Brush: DEBUG Vertical RGB Stripes

    BlackInk Brush: DEBUG Vertical RGB Stripes

    Heute nochmal zurück zu einer alternativen Version eines meiner CRT-Pinsel gegangen und da lag bei mir glatt Armin Hofmanns „Methodik der Form- und Bildgestaltung“ auf dem Tisch, dessen Cover mich fasziniert. Was läge da näher, als eine kleine Studie zu machen, um einen Pinsel auszuprobieren?

    Der Code:

    cfg {
    	name = "DEBUG Vertical RGB Stripes";
    	renderingTime = 60;
    }

    float4 main(idatas i) {
    	// Normalize stroke space UVs
    	box2 b = box2FromCenterAxe(i.strokeStartPos, length(i.strokePos - i.strokeStartPos), normalizeSafe(i.strokePos - i.strokeStartPos));
    	float2 uv = 4 * b.toCenter(i.pos) / b.size;

    	// Scale up horizontal frequency
    	float stripe = floor(uv.x * 60); // visible stripes

    	// Simple stripe pattern: R, G, B
    	float3 col = float3(0.0, 0.0, 0.0);
    	if (mod(stripe, 3) == 0) {
    		col.r = 1.0;
    	} else if (mod(stripe, 3) == 1) {
    		col.g = 1.0;
    	} else {
    		col.b = 1.0;
    	}

    	return float4(col, 1.0);
    }
  • BlackInk Brush: CRT Melt (Procedural)

    BlackInk Brush: CRT Melt (Procedural)

    Zwischen den Seiten von Neuromancer, und Zen & The Art of the Macintosh, habe ich wieder ChatGPT ausgepackt, und mit Hilfe folgender Dokumente BSL Doc und BSL Samples, diesen Pinsel rekonstruiert:1

    cfg{
        name = "CRT Melt (Procedural)";
    }

    globals{

        uiTab "CRT";

        float rgbOffset = 0.03;
        {
            uiTab = "CRT";
            uiName = "RGB Separation";
            uiMin = 0;
            uiMax = 0.2;
        }

        float meltStrength = 0.5;
        {
            uiTab = "CRT";
            uiName = "Vertical Melt";
            uiMin = 0;
            uiMax = 2;
        }

        float wobbleStrength = 0.3;
        {
            uiTab = "CRT";
            uiName = "Horizontal Wobble";
            uiMin = 0;
            uiMax = 2;
        }
    }

    float4 main( idatas i )
    {
        // ----- stroke space -----
        box2 b = box2FromCenterAxe(
            i.strokeStartPos,
            length(i.strokePos - i.strokeStartPos),
            normalizeSafe(i.strokePos - i.strokeStartPos)
        );

        float2 uv = b.toCenter(i.pos) / b.size;

        // ----- CRT distortions -----
        float melt = uv.y + sin( uv.x * 10 + i.time * 2 ) * meltStrength;
        float wobble = sin( uv.y * 40 + i.time * 4 ) * wobbleStrength;

        // ----- RGB sampling positions -----
        float ur = uv.x + wobble + rgbOffset;
        float ug = uv.x + wobble;
        float ub = uv.x + wobble - rgbOffset;

        // ----- stripe signal -----
        float sr = step( 0, sin( ur * 60 ) );
        float sg = step( 0, sin( ug * 60 ) );
        float sb = step( 0, sin( ub * 60 ) );

        float3 col = float3( sr, sg, sb );

        return float4( col, 1.0 );
    }

    Das dabei entstandene ChatGPT‑Projekt kann man bis auf weiteres hier abrufen und selbst verwenden, um eigene Pinsel für BlackInk zu entwickeln.

    1. Die Dokumente habe ich auf https://steamcommunity.com/app/233680/discussions/0/4031351002388283519/ gefunden ↩︎

  • Fix für titellose Posts in WordPress, für SEO, GEO, und Social Media

    Weil ich mehrere Microblogging-Kategorien habe, die keine Titel brauchen, hier ein Fix für das Erstellen eines Pseudotitels für SEO, GEO, und Social-Media-Links:

    // Shared function for title-less posts in certain categories
    function mb_title_for_titleless_notes( $title ) {

        if ( ! is_singular( 'post' ) ) {
            return $title;
        }

        global $post;

        // Only act if the post has no title
        if ( trim( $post->post_title ) !== '' ) {
            return $title;
        }

        // Get categories
        $categories = get_the_category( $post->ID );
        if ( empty( $categories ) ) {
            return $title;
        }

        // Allowed categories
        $allowed = [ 'macht', 'notiert', 'liest', 'hoert', 'schaut', 'spielt' ];
        $matched_category = null;

        foreach ( $categories as $cat ) {
            if ( in_array( $cat->slug, $allowed, true ) ) {
                $matched_category = $cat;
                break;
            }
        }

        if ( ! $matched_category ) {
            return $title;
        }

        // Build replacement title
        $date = get_the_date( 'j. F Y, G:i', $post ); // German 
        $category_name = $matched_category->name;

        // Example: "Notiert: 9. Januar 2026, 9:46 Uhr - Mario Breskic"
        return sprintf(
            '%s: %s Uhr - Mario Breskic',
            $category_name,
            $date
        );
    }

    // HTML <title>
    add_filter( 'wpseo_title', 'mb_title_for_titleless_notes', 20 );

    // Open Graph <meta property="og:title">
    add_filter( 'wpseo_opengraph_title', 'mb_title_for_titleless_notes', 20 );

    // Twitter <meta name="twitter:title">
    add_filter( 'wpseo_twitter_title', 'mb_title_for_titleless_notes', 20 );
    // Built with ChatGPT

  • Dateiumbenennung nach Velsz in Bridge

    Wir machen das in zwei Stufen: zuerst bereinigen wir alle üblichen Datumsangaben in dem Ordner, in dem wir die Umbenennung vornehmen wollen, dann machen wir die Umbenennung in Bridge.

    Vorbereitungsskript zur Bereinigung von Dateinamen (vor der Umbenennung in Adobe Bridge)

    Mein Python-Skript dient dazu, Datumseinträge aus Dateinamen zu entfernen, bevor die eigentliche Umbenennung mit Adobe Bridge erfolgt. Es hilft mir dabei, doppelte oder inkonsistente Datumsangaben zu vermeiden, wenn Bridge später ein neues Datum hinzufügt.

    Was mein Skript macht

    • Durchsucht den Ordner, in dem sich das Skript befindet
    • Erkennt typische Datumsformate im Dateinamen:
      • YYYY-MM-DD (z. B. 2023-08-07)
      • DD-MM-YYYY (z. B. 07-08-2023)
      • YYYYMMDD oder DDMMYYYY (z. B. 20230807)
      • YYMMDD oder DDMMYY (z. B. 230807)
    • Entfernt diese Datumsbestandteile aus dem Dateinamen
    • Lässt die Dateiendung unverändert
    • Gibt eine Rückmeldung, ob eine Datei umbenannt wurde oder nicht (aber nur, wenn man über Commandline/Konsole aufruft)

    Anwendung

    1. Ich speichere das Skript im gleichen Ordner wie die zu bereinigenden Dateien.
    2. Dann führe ich das Skript aus (z. B. mit Python über die Konsole) und dann
    3. Starte ich Adobe Bridge und wende meine Umbenennungsvorlage an.

    Nachfolgend das Python-Script, das ich verwende. Einfach markieren und kopieren, dann beispielsweise als rename_cleaner.py speichern.

    import os
    import re

    # 📍 Get the folder where the script is located
    folder_path = os.path.dirname(os.path.abspath(__file__))

    # 🧠 Regex pattern to match common date formats in filenames
    date_pattern = re.compile(
        r'(\d{4}-\d{2}-\d{2})|'      # YYYY-MM-DD
        r'(\d{2}-\d{2}-\d{4})|'      # DD-MM-YYYY
        r'(\d{8})|'                  # YYYYMMDD or DDMMYYYY
        r'(\d{6})'                   # YYMMDD or DDMMYY
    )

    # 🚀 Loop through files in the folder
    for filename in os.listdir(folder_path):
        file_path = os.path.join(folder_path, filename)

        # Skip folders
        if not os.path.isfile(file_path):
            continue

        name, ext = os.path.splitext(filename)

        # 🧹 Remove date patterns from filename
        cleaned_name = date_pattern.sub('', name).strip('-_ ')

        # 🏷️ Build new filename
        new_filename = f"{cleaned_name}{ext}"
        new_path = os.path.join(folder_path, new_filename)

        # 🔁 Rename file if name changed
        if filename != new_filename:
            os.rename(file_path, new_path)
            print(f"✅ Renamed: {filename} → {new_filename}")
        else:
            print(f"⏩ Skipped (no change): {filename}")

    Anleitung zur Verwendung der Batch-Umbenennungsvorlage in Adobe Bridge

    Dateiname der Vorlage: standard-nach-velsz.setting
    Kompatibel mit: Adobe Bridge 2022, 2023, 2024

    So verwendest du meine Vorlage nach Velsz1

    1. Datei kopieren: Kopiere die Datei standard-nach-velsz.setting in folgenden Ordner auf deinem Computer:

    Windows:

    C:\Users\<USERNAME>\AppData\Roaming\Adobe\Bridge <version>\Batch Rename Settings\

    macOS:

    /Users/<USERNAME>/Library/Application Support/Adobe/Bridge <version>/Batch Rename Settings2

    1. Starte Adobe Bridge.
    2. Markiere alle Dateien, die umbenannt werden sollen.
    3. Gehe zu Werkzeuge > Stapelumbenennung
    4. Lade die heruntergeladene Vorlage standard-nach-velsz, oder:
    5. Wähle folgende Einstellungen
      • Zielordner: Gleicher Ordner (oder ein neuer)
      • Neuer Dateiname:
        • Datum/Uhrzeit. Erstellungsdatum. JJJJMMTT (YYYMMDD)
        • Text: –
        • Beibehaltener Dateiname. Name. Kleinbuchstaben.
    6. Klicke auf Umbenennen, um die Änderungen anzuwenden.
    1. Vergleiche dazu u.a. „Lightroom Classic und CC: das umfassende Handbuch“ von István Velsz ↩︎
    2. Dank für den richtigen Pfad an wckdtalls Kommentar hier: https://community.adobe.com/t5/bridge-discussions/batch-rename-presets/m-p/13085459#M35134 ↩︎

  • Artikellinks aus WordPress in Linkwarden speichern

    Ein kurzer Snippet zum Ausprobieren. Benötigt WordPress und Linkwarden.1 Damit werden alle Links, die sich in einem Artikel bestimmter Kategorien befinden, beim Veröffentlichen zum Speichern an Linkwarden geschickt. Linkwarden schickt diese dann auch an archive.org, damit sie auch öffentlich verfügbar bleiben.

    Kontext dazu: Mein Mastodon‑Post hier, und dieser Bluesky‑Post.

    // Hooks into the WordPress publish_post action.
    // When a post is published, it triggers the send_post_links_to_linkwarden function.
    add_action('publish_post', 'send_post_links_to_linkwarden', 10, 2);

    function send_post_links_to_linkwarden($post_ID, $post) {
        // Only proceed if the post is in one of these categories.
        $preferred_categories = ['CHANGE_ME', 'CHANGE_ME_TOO'];

        // Set post_title
        $post_title = sanitize_text_field($post->post_title);


        // Get the category slugs of the published post.
        $post_categories = wp_get_post_categories($post_ID, ['fields' => 'slugs']);
        
        // Skip processing if the post doesn't belong to one of the preferred categories.
        if (empty(array_intersect($preferred_categories, $post_categories))) {
            error_log("[Linkwarden] Skipping post ID $post_ID because it is not in preferred categories.");
            return;
        }

        // Define the Linkwarden API base URL and access token.
        $api_base_url = ' https://YOUR_LINKWARDEN_URL/api/v1';
        $api_token = 'YOUR_API_TOKEN';

        // Extract all URLs from the post content.
        $content = $post->post_content;
        $urls = wp_extract_urls($content);

        // Exit if no URLs were found in the post.
        if (empty($urls)) {
            error_log("[Linkwarden] No URLs found in post ID $post_ID");
            return;
        }

        // Remove duplicate URLs.
        $urls = array_unique($urls);

        // Send each URL found in the post to the Linkwarden API.
        foreach ($urls as $url) {
            // Create the body of the request with the URL, post title as title and tag.
            $body = [
                'url'   => $url,
                'title' => $post->post_title,
                'tags'  => [ ['name'=> $post_title] ],
                'collectionId' => [
                    'id' => COLLECTION_ID_NUMBER_NO_QUOTES_FOR_ME_PLEASE    
                    ],
            ];
            
            // Make a POST request to the Linkwarden /links endpoint.
            $response = wp_remote_post("{$api_base_url}/links", [
                'headers' => [
                    'Authorization' => 'Bearer ' . $api_token,
                    'Content-Type'  => 'application/json',
                ],
                'body'    => wp_json_encode($body),
                'timeout' => 10,
            ]);
            
            // Log an error if the HTTP request fails.
            if (is_wp_error($response)) {
                error_log("[Linkwarden] HTTP request error for URL $url: " . $response->get_error_message());
                continue;
            }
            
            // Check the response code to confirm successful addition.
            $code = wp_remote_retrieve_response_code($response);
            if ($code !== 201 && $code !== 200) {
                error_log("[Linkwarden] Unexpected response code $code for URL $url. Response: " . wp_remote_retrieve_body($response));
            } else {
                error_log("[Linkwarden] Successfully added URL $url from post ID $post_ID");
            }
        }
    }
    1. Getestet mit selbst-gehostetem Linkwarden als Docker-Volume. ↩︎

  • CRT-Pixel-Shader-Brush für BlackInk

    Dieses kurze Shader-Skript erzeugt RGB-Streifen entlang der Pinselbewegung und eignet sich als visuelles Experiment oder Ausgangspunkt für eigene Brush-Designs. Es kann direkt in BlackInk eingefügt werden – dazu einfach den Code in den „Brush Pixel Shader Editor“ kopieren und als neue Konfiguration speichern.

    Die Streifen entstehen durch eine einfache Modulo-Logik: Jede dritte Spalte wird abwechselnd rot, grün oder blau eingefärbt. Die Frequenz lässt sich über die uv.x-Skalierung anpassen. Die Berechnung erfolgt auf Basis der Pinselrichtung und ‑länge, wodurch das Muster dynamisch auf die Strichführung reagiert.

    cfg {
     name = "Vertical RGB Stripes";
     renderingTime = 60;
    }

    float4 main(idatas i) {
     // Normalize stroke space UVs
     box2 b = box2FromCenterAxe(i.strokeStartPos, length(i.strokePos - i.strokeStartPos), normalizeSafe(i.strokePos - i.strokeStartPos));
     float2 uv = 4 * b.toCenter(i.pos) / b.size;

     // Scale up horizontal frequency
     float stripe = floor(uv.x * 60); // visible stripes

     // Simple stripe pattern: R, G, B
     float3 col = float3(0.0, 0.0, 0.0);
     if (mod(stripe, 3) == 0) {
      col.r = 1.0;
     } else if (mod(stripe, 3) == 1) {
      col.g = 1.0;
     } else {
      col.b = 1.0;
     }

     return float4(col, 1.0);
    }