1 files changed, 128 insertions, 0 deletions
diff --git a/lib/private/Preview/Bitmap.php b/lib/private/Preview/Bitmap.php
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+++ b/lib/private/Preview/Bitmap.php
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+<?php
+
+/**
+ * SPDX-FileCopyrightText: 2016-2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-FileCopyrightText: 2016 ownCloud, Inc.
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+namespace OC\Preview;
+
+use Imagick;
+use OCP\Files\File;
+use OCP\IImage;
+use Psr\Log\LoggerInterface;
+
+/**
+ * Creates a PNG preview using ImageMagick via the PECL extension
+ *
+ * @package OC\Preview
+ */
+abstract class Bitmap extends ProviderV2 {
+	/**
+	 * List of MIME types that this preview provider is allowed to process.
+	 *
+	 * These should correspond to the MIME types *identified* by Imagemagick
+	 * for files to be processed by this provider. These do / will not
+	 * necessarily need to match the MIME types stored in the database
+	 * (which are identified by IMimeTypeDetector).
+	 *
+	 * @return string Regular expression
+	 */
+	abstract protected function getAllowedMimeTypes(): string;
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
+		$tmpPath = $this->getLocalFile($file);
+		if ($tmpPath === false) {
+			\OC::$server->get(LoggerInterface::class)->error(
+				'Failed to get thumbnail for: ' . $file->getPath(),
+				['app' => 'core']
+			);
+			return null;
+		}
+
+		// Creates \Imagick object from bitmap or vector file
+		try {
+			$bp = $this->getResizedPreview($tmpPath, $maxX, $maxY);
+		} catch (\Exception $e) {
+			\OC::$server->get(LoggerInterface::class)->info(
+				'File: ' . $file->getPath() . ' Imagick says:',
+				[
+					'exception' => $e,
+					'app' => 'core',
+				]
+			);
+			return null;
+		}
+
+		$this->cleanTmpFiles();
+
+		//new bitmap image object
+		$image = new \OCP\Image();
+		$image->loadFromData((string)$bp);
+		//check if image object is valid
+		return $image->valid() ? $image : null;
+	}
+
+	/**
+	 * Returns a preview of maxX times maxY dimensions in PNG format
+	 *
+	 *    * The default resolution is already 72dpi, no need to change it for a bitmap output
+	 *    * It's possible to have proper colour conversion using profileimage().
+	 *    ICC profiles are here: http://www.color.org/srgbprofiles.xalter
+	 *    * It's possible to Gamma-correct an image via gammaImage()
+	 *
+	 * @param string $tmpPath the location of the file to convert
+	 * @param int $maxX
+	 * @param int $maxY
+	 *
+	 * @return \Imagick
+	 *
+	 * @throws \Exception
+	 */
+	private function getResizedPreview($tmpPath, $maxX, $maxY) {
+		$bp = new Imagick();
+
+		// Validate mime type
+		$bp->pingImage($tmpPath . '[0]');
+		$mimeType = $bp->getImageMimeType();
+		if (!preg_match($this->getAllowedMimeTypes(), $mimeType)) {
+			throw new \Exception('File mime type does not match the preview provider: ' . $mimeType);
+		}
+
+		// Layer 0 contains either the bitmap or a flat representation of all vector layers
+		$bp->readImage($tmpPath . '[0]');
+
+		$bp = $this->resize($bp, $maxX, $maxY);
+
+		$bp->setImageFormat('png');
+
+		return $bp;
+	}
+
+	/**
+	 * Returns a resized \Imagick object
+	 *
+	 * If you want to know more on the various methods available to resize an
+	 * image, check out this link : @link https://stackoverflow.com/questions/8517304/what-the-difference-of-sample-resample-scale-resize-adaptive-resize-thumbnail-im
+	 *
+	 * @param \Imagick $bp
+	 * @param int $maxX
+	 * @param int $maxY
+	 *
+	 * @return \Imagick
+	 */
+	private function resize($bp, $maxX, $maxY) {
+		[$previewWidth, $previewHeight] = array_values($bp->getImageGeometry());
+
+		// We only need to resize a preview which doesn't fit in the maximum dimensions
+		if ($previewWidth > $maxX || $previewHeight > $maxY) {
+			// TODO: LANCZOS is the default filter, CATROM could bring similar results faster
+			$bp->resizeImage($maxX, $maxY, imagick::FILTER_LANCZOS, 1, true);
+		}
+
+		return $bp;
+	}
+}