first version of the new previewer lib. It currently only created previews/thumbnails for images. It get´s more interesting when we add PDFs, movies, mp3, text files and more...

lib/preview.php

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+<?php
+/**
+ * Copyright (c) 2012 Frank Karlitschek frank@owncloud.org
+ * This file is licensed under the Affero General Public License version 3 or
+ * later.
+ * See the COPYING-README file.
+ */
+
+/*
+TODO:
+  - delete thumbnails if files change. 
+  - movies support
+  - pdf support
+  - mp3/id3 support
+  - more file types
+
+*/
+
+
+
+class OC_Preview {
+        
+
+	/**
+	 * @brief return a preview of a file
+	 * @param $file The path to the file where you want a thumbnail from
+	 * @param $maxX The maximum X size of the thumbnail. It can be smaller depending on the shape of the image
+	 * @param $maxY The maximum Y size of the thumbnail. It can be smaller depending on the shape of the image
+	 * @return image
+	*/
+	static public function show($file,$maxX,$maxY) {
+		$mimetype=explode('/',OC_FileSystem::getMimeType($file));
+		if($mimetype[0]=='imaage'){
+			OCP\Response::enableCaching(3600 * 24); // 24 hour
+			$image=OC_PreviewImage::getThumbnail($file,$maxX,$maxY,false);
+			$image->show();
+		}else{
+			header('Content-type: image/png');
+			OC_PreviewUnknown::getThumbnail($maxX,$maxY);
+		}
+	}
+
+
+}
+
+
+
+class OC_PreviewImage {
+
+	// the thumbnail cache folder
+	const THUMBNAILS_FOLDER = 'thumbnails';
+
+        public static function getThumbnail($path,$maxX,$maxY,$scalingup) {
+		$thumbnails_view = new \OC_FilesystemView('/'.\OCP\User::getUser() .'/'.self::THUMBNAILS_FOLDER);
+
+		// is a preview already in the cache?
+                if ($thumbnails_view->file_exists($path.'-'.$maxX.'-'.$maxY.'-'.$scalingup)) {
+                        return new \OC_Image($thumbnails_view->getLocalFile($path.'-'.$maxX.'-'.$maxY.'-'.$scalingup));
+                }
+		
+		// does the sourcefile exist?
+                if (!\OC_Filesystem::file_exists($path)) {
+                        \OC_Log::write('Preview', 'File '.$path.' don\'t exists', \OC_Log::WARN);
+                        return false;
+                }
+
+		// open the source image
+                $image = new \OC_Image();
+                $image->loadFromFile(\OC_Filesystem::getLocalFile($path));
+                if (!$image->valid()) return false;
+
+		// fix the orientation
+                $image->fixOrientation();
+	
+		// calculate the right preview size
+		$Xsize=$image->width();
+		$Ysize=$image->height();
+		if (($Xsize/$Ysize)>($maxX/$maxY)) {
+			$factor=$maxX/$Xsize;
+		} else {
+			$factor=$maxY/$Ysize;
+		}
+		
+		// only scale up if requested
+		if($scalingup==false) {
+			if($factor>1) $factor=1;
+		}
+		$newXsize=$Xsize*$factor;
+		$newYsize=$Ysize*$factor;
+
+		// resize
+                $ret = $image->preciseResize($newXsize, $newYsize);
+                if (!$ret) {
+                        \OC_Log::write('Preview', 'Couldn\'t resize image', \OC_Log::ERROR);
+                        unset($image);
+                        return false;
+                }
+			
+		// store in cache
+                $l = $thumbnails_view->getLocalFile($path.'-'.$maxX.'-'.$maxY.'-'.$scalingup);
+                $image->save($l);
+
+                return $image;
+        }
+
+
+
+}
+
+
+class OC_PreviewUnknown {
+        public static function getThumbnail($maxX,$maxY) {
+			
+		// check if GD is installed
+		if(!extension_loaded('gd') || !function_exists('gd_info')) {
+			OC_Log::write('preview', __METHOD__.'(): GD module not installed', OC_Log::ERROR);
+			return false;
+		}
+
+		// create a white image
+		$image = imagecreatetruecolor($maxX, $maxY);
+		$color = imagecolorallocate($image, 255, 255, 255);
+		imagefill($image, 0, 0, $color);
+
+		// output the image
+		imagepng($image);
+		imagedestroy($image);
+        }
+
+}
+

lib/public/preview.php

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+<?php
+/**
+* ownCloud
+*
+* @author Frank Karlitschek
+* @copyright 2012 Frank Karlitschek frank@owncloud.org
+*
+* This library is free software; you can redistribute it and/or
+* modify it under the terms of the GNU AFFERO GENERAL PUBLIC LICENSE
+* License as published by the Free Software Foundation; either
+* version 3 of the License, or any later version.
+*
+* This library is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU AFFERO GENERAL PUBLIC LICENSE for more details.
+*
+* You should have received a copy of the GNU Affero General Public
+* License along with this library.  If not, see <http://www.gnu.org/licenses/>.
+*
+*/
+
+/**
+ * Public interface of ownCloud for apps to use.
+ * Preview Class.
+ *
+ */
+
+// use OCP namespace for all classes that are considered public.
+// This means that they should be used by apps instead of the internal ownCloud classes
+namespace OCP;
+
+/**
+ * This class provides functions to render and show thumbnails and previews of files
+ */
+class Preview {
+
+	/**
+	 * @brief return a preview of a file
+	 * @param $file The path to the file where you want a thumbnail from
+	 * @param $maxX The maximum X size of the thumbnail. It can be smaller depending on the shape of the image
+	 * @param $maxY The maximum Y size of the thumbnail. It can be smaller depending on the shape of the image
+	 * @param $scaleup Scale smaller images up to the thumbnail size or not. Might look ugly
+	 * @return image
+	 */
+	public static function show($file,$maxX=100,$maxY=75,$scaleup=false) {
+		return(\OC_Preview::show($file,$maxX,$maxY,$scaleup));
+	}
+
+}