ext_localconf.php

<?php

/*
 * This file is part of the TYPO3 responsive images project.
 *
 * It is free software; you can redistribute it and/or modify it under
 * the terms of the GNU General Public License, either version 2
 * of the License, or any later version.
 *
 * For the full copyright and license information, please read
 * LICENSE file that was distributed with this source code.
 *
 */

if (!defined('TYPO3_MODE')) {
    die('Access denied');
}

call_user_func(function () {
    /** @var \TYPO3\CMS\Core\Resource\Rendering\RendererRegistry $rendererRegistry */
    $rendererRegistry = \TYPO3\CMS\Core\Resource\Rendering\RendererRegistry::getInstance();
    $rendererRegistry->registerRendererClass(\Codemonkey1988\ResponsiveImages\Resource\Rendering\ResponsiveImageRenderer::class);

    $signalSlotDispatcher = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\TYPO3\CMS\Extbase\SignalSlot\Dispatcher::class);
    $signalSlotDispatcher->connect(
        \TYPO3\CMS\Core\Resource\ResourceStorage::class,
        \TYPO3\CMS\Core\Resource\Service\FileProcessingService::SIGNAL_PreFileProcess,
        \Codemonkey1988\ResponsiveImages\Signal\FileProcessing::class,
        'preProcess'
    );
});