Improve the performance when creating previews for thousands of items by the following strategy:

 - The previews for currently visible items are created before
   the previews for invisible items.
 - If the user changes the visible area by using the scrollbars,
   all pending previews get paused. As soon as the user stays
   on the same position for a short delay, the previews are
   resumed. Also in this case the previews for the visible items
   are generated first.

svn path=/trunk/KDE/kdebase/apps/; revision=815480

1 files changed, 51 insertions, 5 deletions

diff --git a/src/iconmanager.h b/src/iconmanager.h
index f72811c27..e9d7c9b78 100644
--- a/src/iconmanager.h
+++ b/src/iconmanager.h
@@ -38,6 +38,15 @@ class QAbstractItemView;
  * Per default a preview is generated for each item.
  * Additionally the clipboard is checked for cut items.
  * The icon state for cut items gets dimmed automatically.
+ *
+ * The following strategy is used when creating previews:
+ * - The previews for currently visible items are created before
+ *   the previews for invisible items.
+ * - If the user changes the visible area by using the scrollbars,
+ *   all pending previews get paused. As soon as the user stays
+ *   on the same position for a short delay, the previews are
+ *   resumed. Also in this case the previews for the visible items
+ *   are generated first.
  */
 class IconManager : public QObject
 {
@@ -73,11 +82,25 @@ private slots:
     void updateCutItems();
 
     /**
-     * Dispatches the preview queue m_previews block by block within
+     * Dispatches the preview queue  block by block within
      * time slices.
      */
     void dispatchPreviewQueue();
 
+    /**
+     * Pauses all preview jobs and invokes IconManager::resumePreviews()
+     * after a short delay. Is invoked as soon as the user has moved
+     * a scrollbar.
+     */
+    void pausePreviews();
+
+    /**
+     * Resumes the previews that have been paused after moving the
+     * scrollbar. The previews for the current visible area are
+     * generated first.
+     */
+    void resumePreviews();
+
 private:
     /**
      * Replaces the icon of the item with the \a url by the preview pixmap
@@ -107,13 +130,17 @@ private:
      */
     void limitToSize(QPixmap& icon, const QSize& maxSize);
 
+    /**
+     * Starts a new preview job for the items \a to m_previewJobs
+     * and triggers the preview timer.
+     */
+    void startPreviewJob(const KFileItemList& items);
+
     /** Kills all ongoing preview jobs. */
-    void killJobs();
+    void killPreviewJobs();
 
 private:
-    /**
-     * Remembers the pixmap for an item specified by an URL.
-     */
+    /** Remembers the pixmap for an item specified by an URL. */
     struct ItemInfo
     {
         KUrl url;
@@ -122,14 +149,33 @@ private:
 
     bool m_showPreview;
 
+    /**
+     * True, if m_pendingItems and m_dispatchedItems should be
+     * cleared when the preview jobs have been finished.
+     */
+    bool m_clearItemQueues;
+
     QAbstractItemView* m_view;
     QTimer* m_previewTimer;
+    QTimer* m_scrollAreaTimer;
     QList<KJob*> m_previewJobs;
     DolphinModel* m_dolphinModel;
     DolphinSortFilterProxyModel* m_proxyModel;
 
     QList<ItemInfo> m_cutItemsCache;
     QList<ItemInfo> m_previews;
+
+    /**
+     * Contains the URLs of all items where a preview must be generated, but
+     * where the preview job has not dispatched the items yet.
+     */
+    QList<KUrl> m_pendingItems;
+
+    /**
+     * Containts the URLs of all items, where a preview has already been
+     * generated by the preview jobs.
+     */
+    QList<KUrl> m_dispatchedItems;
 };
 
 inline bool IconManager::showPreview() const