ImageManager/ThumbnailStorage.h

   1 /* Copyright (C) 2008 Henner Zeller <h.zeller@acm.org>
   2
   3    This program is free software; you can redistribute it and/or
   4    modify it under the terms of the GNU General Public
   5    License as published by the Free Software Foundation; either
   6    version 2 of the License, or (at your option) any later version.
   7
   8    This program is distributed in the hope that it will be useful,
   9    but WITHOUT ANY WARRANTY; without even the implied warranty of
  10    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11    General Public License for more details.
  12
  13    You should have received a copy of the GNU General Public License
  14    along with this program; see the file COPYING.  If not, write to
  15    the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  16    Boston, MA 02110-1301, USA.
  17 */
  18
  19 #ifndef THUMBNAIL_STORAGE_H
  20 #define THUMBNAIL_STORAGE_H
  21
  22 #include <qmap.h>
  23 #include <qstring.h>
  24 #include <QMutex>
  25 #include <QSet>
  26 class QImage;
  27
  28 namespace ImageManager {
  29
  30 /**
  31  * Interface of a backend to store thumbnails.
  32  * Implementations of ThumbnailStorage must be thread save.
  33  */
  34 class ThumbnailStorage {
  35 public:
  36     virtual ~ThumbnailStorage() {}
  37
  38     /** Store an image under the given key. Returns success. */
  39     virtual bool store(const QString& key, const QImage& image) = 0;
  40
  41     /**
  42      * Tries to retrieve an image stored under the given key. On success,
  43      * returns 'true' and fills in the image.
  44      */
  45     virtual bool retrieve(const QString& key, QImage* image) = 0;
  46
  47     /**
  48      * Remove an image under the given key from the storage.
  49      */
  50     virtual void remove(const QString& key) = 0;
  51
  52     /**
  53      * Check if the thumbnail with the given key exists. Use if you don't
  54      * want to load the thumbnail but check if you would need go generate it.
  55      */
  56     virtual bool exists(const QString& key) = 0;
  57 };
  58
  59
  60 /**
  61  * Default implementation of the ThumbnailStorage. It stores images
  62  * in ~/.thumbnails/${key}.${imageFormat}.
  63  */
  64 class FileThumbnailStorage : public ThumbnailStorage {
  65 public:
  66     /**
  67      * construct a FileThumbnailStorage. Store the images in the given
  68      * "imageFormat", which can be 'png', 'ppm', 'jpg'. The 'png' format
  69      * would be the standard format to be compatible with other
  70      * applications (see <http://jens.triq.net/thumbnail-spec/>), but turns
  71      * out that the 'ppm' format seems to be much faster.
  72      * If "imageFormat" is NULL, we fall back to 'ppm' as default.
  73      */
  74     FileThumbnailStorage(const QString & imageFormat);
  75
  76     virtual bool store(const QString& key, const QImage& image);
  77     virtual bool retrieve(const QString& key, QImage* image);
  78     virtual void remove(const QString& key);
  79     virtual bool exists(const QString& key);
  80
  81 private:
  82     QString keyToPath(const QString& key);
  83     QMutex _cacheLock;
  84     QSet<QString> _existenceCache;
  85     QString _imageFormat;
  86 };
  87
  88 // If Filesystem-IO makes trouble, we could consider implementing a
  89 // store in BerkeleyDB or SQLite...
  90
  91 #ifdef TESTING_MEMORY_THUMBNAIL_CACHING
  92 class MemoryThumbnailStorage : public ThumbnailStorage {
  93 public:
  94     MemoryThumbnailStorage(const char* imageFormat);
  95     virtual bool store(const QString& key, const QImage& image);
  96     virtual bool retrieve(const QString& key, QImage* image);
  97     virtual void remove(const QString&) {}
  98     virtual bool exists(const QString& key);
  99
 100 private:
 101     typedef QMap<QString, QByteArray> ImageCache;
 102     // TODO: add mutex, if tested in multiple threads
 103     ImageCache _cache;
 104     const char* const _imageFormat;
 105 };
 106 #endif
 107
 108 }  // end namespace ImageManager
 109
 110 #endif /* THUMBNAIL_STORAGE_H */