Dive pictures: automatically recalculate thumbnails

If a thumbnail and the original picture can be accessed and the
modification date of the thumbnail is before the modification date
of the picture, recalculate the thumbnail.

This causes more disk access and might give strange effects for
picture files with messed up file timestamps (i.e. lying in the
future) or messed up computer clocks (i.e. running in the past).
Therefore, add a preference option to disable the new behavior.
Default is set to enabled.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

1 files changed, 17 insertions, 1 deletions

diff --git a/core/imagedownloader.cpp b/core/imagedownloader.cpp
index 0c72f3381..da5c86b99 100644
--- a/core/imagedownloader.cpp
+++ b/core/imagedownloader.cpp
@@ -151,8 +151,24 @@ static QImage getThumbnailFromCache(const QString &picture_filename)
 	QString filename = thumbnailFileName(picture_filename);
 	if (filename.isEmpty())
 		return QImage();
-
 	QFile file(filename);
+
+	if (prefs.auto_recalculate_thumbnails) {
+		// Check if thumbnails is older than the (local) image file
+		QString filenameLocal = localFilePath(qPrintable(picture_filename));
+		QFileInfo pictureInfo(filenameLocal);
+		QFileInfo thumbnailInfo(file);
+		if (pictureInfo.exists() && thumbnailInfo.exists()) {
+			QDateTime pictureTime = pictureInfo.lastModified();
+			QDateTime thumbnailTime = thumbnailInfo.lastModified();
+			if (pictureTime.isValid() && thumbnailTime.isValid() && thumbnailTime < pictureTime) {
+				// Both files exist, have valid timestamps and thumbnail was calculated before picture.
+				// Return an empty thumbnail to signal recalculation of the thumbnail
+				return QImage();
+			}
+		}
+	}
+
 	if (!file.open(QIODevice::ReadOnly))
 		return QImage();
 	QDataStream stream(&file);