thumbnailcache.cpp Example File

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 #include "thumbnailcache.h"

 #include "thumbnailmodel.h"

 #include <QtCore/qcryptographichash.h>
 #include <QtCore/qcoreapplication.h>
 #include <QtCore/qcoreevent.h>
 #include <QtCore/qdir.h>
 #include <QtCore/qurl.h>
 #include <QtGui/qimagereader.h>
 #include <QtGui/qpixmap.h>

 #if (QT_VERSION < QT_VERSION_CHECK(4, 7, 0))
 uint qHash(const QUrl &url) { return qHash(url.toString()); }
 #endif

 class Thumbnail
 {
 public:
     Thumbnail(const QUrl &url)
         : url(url)
     {
     }

     const QUrl url;
     QPixmap pixmap;

 private:
     ThumbnailCache *cache;
 };

 class ThumbnailEvent : public QEvent
 {
 public:
     ThumbnailEvent(const QUrl &url, const QImage &image)
         : QEvent(QEvent::User)
         , url(url)
         , image(image)
     {
     }

     const QUrl url;
     const QImage image;
 };

 ThumbnailCache::ThumbnailCache(QObject *parent)
     : QThread(parent)
 #if defined(Q_OS_SYMBIAN) || defined(Q_WS_MAEMO_5) || defined(Q_WS_MAEMO_6)
     , cache(25)
 #else
     , cache(150)
 #endif
     , cancelled(false)
 {
     start(QThread::LowestPriority);
 }

 ThumbnailCache::~ThumbnailCache()
 {
     {
         QMutexLocker locker(&mutex);

         cancelled = true;

         waitCondition.wakeOne();
     }
     wait();
 }

 QPixmap ThumbnailCache::thumbnail(const QUrl &url)
 {
     QMutexLocker locker(&mutex);

     if (Thumbnail *thumbnail = cache.object(url)) {
         return thumbnail->pixmap;
     } else {
         pendingUrls.enqueue(url);

         cache.insert(url, new Thumbnail(url));

         waitCondition.wakeOne();

         return QPixmap();
     }
 }

 bool ThumbnailCache::event(QEvent *event)
 {
     if (event->type() == QEvent::User) {
         ThumbnailEvent *thumbnailEvent = static_cast<ThumbnailEvent *>(event);

         QMutexLocker locker(&mutex);

         if (Thumbnail *thumbnail = cache.object(thumbnailEvent->url)) {
             thumbnail->pixmap = QPixmap::fromImage(thumbnailEvent->image);

             locker.unlock();

             emit thumbnailReady();
         }
         return true;
     } else {
         return QThread::event(event);
     }
 }

 void ThumbnailCache::run()
 {
     QMutexLocker locker(&mutex);

     while(!cancelled) {
         if (!pendingUrls.isEmpty()) {
             const QUrl url = pendingUrls.dequeue();

             if (cache.contains(url)) {
                 locker.unlock();
                 QImage image = loadImage(url);
                 locker.relock();

                 if (!image.isNull())
                     QCoreApplication::postEvent(this, new ThumbnailEvent(url, image));
             }
         } else {
             waitCondition.wait(&mutex);
         }
     }
 }

 QImage ThumbnailCache::loadImage(const QUrl &url) const
 {
     const QString fileName = thumbnailPath(url);

     QImageReader reader(fileName);
     reader.setQuality(25);

     if (reader.supportsOption(QImageIOHandler::Size)) {
         QSize size = reader.size();

         if (!reader.supportsOption(QImageIOHandler::ScaledSize)
                 && (size.width() > 1280 || size.height() > 1280)) {
             return QImage();
         }

         if (size.width() > ThumbnailModel::thumbnailSize.width()
                 || size.height() > ThumbnailModel::thumbnailSize.height()) {
             size.scale(ThumbnailModel::thumbnailSize, Qt::KeepAspectRatio);
         }

         reader.setScaledSize(size);
     } else {
         reader.setScaledSize(ThumbnailModel::thumbnailSize);
     }

     return reader.read();
 }

 QString ThumbnailCache::thumbnailPath(const QUrl &url) const
 {
 #if defined(Q_OS_UNIX) && !(defined(Q_OS_SYMBIAN) || defined(Q_OS_MAC))
 #if defined(Q_WS_MAEMO_5)
     QString thumbnailPath = QDir::homePath()
             + QLatin1String("/.thumbnails/cropped/")
             + QCryptographicHash::hash(url.toString().toUtf8(), QCryptographicHash::Md5).toHex()
             + QLatin1String(".jpeg");
 #elif defined(Q_WS_MAEMO_6)
     QString thumbnailPath = QDir::homePath()
             + QLatin1String("/.thumbnails/grid/")
             + QCryptographicHash::hash(url.toString().toUtf8(), QCryptographicHash::Md5).toHex()
             + QLatin1String(".jpeg");
 #else
     QString thumbnailPath = QDir::homePath()
             + QLatin1String("/.thumbnails/normal/")
             + QCryptographicHash::hash(url.toEncoded(), QCryptographicHash::Md5).toHex()
             + QLatin1String(".png");
 #endif
     if (QFile::exists(thumbnailPath))
         return thumbnailPath;
 #endif

     return url.toLocalFile();
 }