Implement different zoom levels for dive photos tab

This implements different zoom levels for the dive photos tab as
suggested by Stefan Fuchs <sfuchs@gmx.de> in #898.
The zoom level can be changed using a slider or CTRL+mousewheel.
Zoom levels range from a third of the standard thumbnail size to
thrice the standard thumbnail size.

Thumbnails are cached in maximum resolution and scaled down on
the fly. Because the profile widget took its pictures from the
photo list model, an extra picture copy with a fixed size had
to be introduced.

The UI is still a bit crude.

Reported-by: Stefan Fuchs <sfuchs@gmx.de>
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

1 files changed, 52 insertions, 16 deletions

diff --git a/qt-models/divepicturemodel.cpp b/qt-models/divepicturemodel.cpp
index ff4e187ae..47e64492b 100644
--- a/qt-models/divepicturemodel.cpp
+++ b/qt-models/divepicturemodel.cpp
@@ -9,25 +9,28 @@
 
 extern QHash <QString, QImage> thumbnailCache;
 static QMutex thumbnailMutex;
+static const int maxZoom = 3;	// Maximum zoom: thrice of standard size
 
-static void scaleImages(PictureEntry &entry)
+static QImage getThumbnailFromCache(const PictureEntry &entry)
 {
 	QMutexLocker l(&thumbnailMutex);
-	if (thumbnailCache.contains(entry.filename) && !thumbnailCache.value(entry.filename).isNull()) {
-		entry.image = thumbnailCache.value(entry.filename);
-		return;
-	}
-	l.unlock();
+	return thumbnailCache.value(entry.filename);
+}
 
-	int dim = defaultIconMetrics().sz_pic;
-	QImage p = SHashedImage(entry.picture);
-	if(!p.isNull()) {
-		p = p.scaled(dim, dim, Qt::KeepAspectRatio);
+static void scaleImages(PictureEntry &entry, int size, int maxSize)
+{
+	QImage thumbnail = getThumbnailFromCache(entry);
+	// If thumbnails were written by an earlier version, they might be smaller than needed.
+	// Rescale in such a case to avoid resizing artifacts.
+	if (thumbnail.isNull() || (thumbnail.size().width() < maxSize && thumbnail.size().height() < maxSize)) {
+		thumbnail = SHashedImage(entry.picture).scaled(maxSize, maxSize, Qt::KeepAspectRatio);
 		QMutexLocker l(&thumbnailMutex);
-		if (!thumbnailCache.contains(entry.filename))
-			thumbnailCache.insert(entry.filename, p);
+		thumbnailCache.insert(entry.filename, thumbnail);
 	}
-	entry.image = p;
+
+	entry.imageProfile = thumbnail.scaled(maxSize / maxZoom, maxSize / maxZoom, Qt::KeepAspectRatio);
+	entry.image = size == maxSize ? thumbnail
+				      : thumbnail.scaled(size, size, Qt::KeepAspectRatio);
 }
 
 DivePictureModel *DivePictureModel::instance()
@@ -36,7 +39,9 @@ DivePictureModel *DivePictureModel::instance()
 	return self;
 }
 
-DivePictureModel::DivePictureModel() : rowDDStart(0), rowDDEnd(0)
+DivePictureModel::DivePictureModel() : rowDDStart(0),
+				       rowDDEnd(0),
+				       zoomLevel(0.0)
 {
 }
 
@@ -48,6 +53,33 @@ void DivePictureModel::updateDivePicturesWhenDone(QList<QFuture<void>> futures)
 	updateDivePictures();
 }
 
+void DivePictureModel::setZoomLevel(int level)
+{
+	zoomLevel = level / 10.0;
+	// zoomLevel is bound by [-1.0 1.0], see comment below.
+	if (zoomLevel < -1.0)
+		zoomLevel = -1.0;
+	if (zoomLevel > 1.0)
+		zoomLevel = 1.0;
+	updateThumbnails();
+	layoutChanged();
+}
+
+void DivePictureModel::updateThumbnails()
+{
+	// Calculate size of thumbnails. The standard size is defaultIconMetrics().sz_pic.
+	// We use exponential scaling so that the central point is the standard
+	// size and the minimum and maximum extreme points are a third respectively
+	// three times the standard size.
+	// Naturally, these three zoom levels are then represented by
+	// -1.0 (minimum), 0 (standard) and 1.0 (maximum). The actual size is
+	// calculated as standard_size*3.0^zoomLevel.
+	int defaultSize = defaultIconMetrics().sz_pic;
+	int maxSize = defaultSize * maxZoom;
+	int size = static_cast<int>(round(defaultSize * pow(maxZoom, zoomLevel)));
+	QtConcurrent::blockingMap(pictures, [size, maxSize](PictureEntry &entry){scaleImages(entry, size, maxSize);});
+}
+
 void DivePictureModel::updateDivePictures()
 {
 	if (!pictures.isEmpty()) {
@@ -68,12 +100,13 @@ void DivePictureModel::updateDivePictures()
 			if (dive->id == displayed_dive.id)
 				rowDDStart = pictures.count();
 			FOR_EACH_PICTURE(dive)
-				pictures.push_back({picture, picture->filename, QImage(), picture->offset.seconds});
+				pictures.push_back({picture, picture->filename, {}, {}, picture->offset.seconds});
 			if (dive->id == displayed_dive.id)
 				rowDDEnd = pictures.count();
 		}
 	}
-	QtConcurrent::blockingMap(pictures, scaleImages);
+
+	updateThumbnails();
 
 	beginInsertRows(QModelIndex(), 0, pictures.count() - 1);
 	endInsertRows();
@@ -100,6 +133,9 @@ QVariant DivePictureModel::data(const QModelIndex &index, int role) const
 		case Qt::DecorationRole:
 			ret = entry.image;
 			break;
+		case Qt::UserRole:	// Used by profile widget to access bigger thumbnails
+			ret = entry.imageProfile;
+			break;
 		case Qt::DisplayRole:
 			ret = QFileInfo(entry.filename).fileName();
 			break;