Dive pictures: Move thumbnail-size to Thumbnailer class

The size of the to-be-created thumbnails was passed from DivePictureModel
to Thumbnailer. This became more and more bothersome, because the size
had to be stored with the request. Calling from Thumbnailer into
DivePictureModel was not an option, since this is not linked to all tests.
Therefore, move these functions to the Thumbnailer class.

Since the maximum thumbnail size is now known to the thumbnailer, the
dummy and failure images can be precalculated, which makes switching
between dives faster.

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

2 files changed, 39 insertions, 9 deletions

diff --git a/core/imagedownloader.cpp b/core/imagedownloader.cpp
index 2949d83d9..cbff1489c 100644
--- a/core/imagedownloader.cpp
+++ b/core/imagedownloader.cpp
@@ -140,7 +140,8 @@ QImage getHashedImage(const QString &file)
 	return res;
 }
 
-Thumbnailer::Thumbnailer()
+Thumbnailer::Thumbnailer() : failImage(QImage(":filter-close").scaled(maxThumbnailSize(), maxThumbnailSize(), Qt::KeepAspectRatio)), // TODO: Don't misuse filter close icon
+			     dummyImage(QImage(":photo-icon").scaled(maxThumbnailSize(), maxThumbnailSize(), Qt::KeepAspectRatio)) // TODO: Don't misuse photo-icon
 {
 	// Currently, we only process one image at a time. Stefan Fuchs reported problems when
 	// calculating multiple thumbnails at once and this hopefully helps.
@@ -200,16 +201,16 @@ static void addThumbnailToCache(const QImage &thumbnail, const QString &picture_
 	file.commit();
 }
 
-void Thumbnailer::processItem(QString filename, int size)
+void Thumbnailer::processItem(QString filename)
 {
 	QImage thumbnail = getThumbnailFromCache(filename);
 
 	if (thumbnail.isNull()) {
 		thumbnail = getHashedImage(filename);
 		if (thumbnail.isNull()) {
-			// TODO: Don't misuse filter close icon
-			thumbnail = QImage(":filter-close").scaled(size, size, Qt::KeepAspectRatio);
+			thumbnail = failImage;
 		} else {
+			int size = maxThumbnailSize();
 			thumbnail = thumbnail.scaled(size, size, Qt::KeepAspectRatio);
 			addThumbnailToCache(thumbnail, filename);
 		}
@@ -220,7 +221,7 @@ void Thumbnailer::processItem(QString filename, int size)
 	workingOn.remove(filename);
 }
 
-QImage Thumbnailer::fetchThumbnail(PictureEntry &entry, int size)
+QImage Thumbnailer::fetchThumbnail(PictureEntry &entry)
 {
 	QMutexLocker l(&lock);
 
@@ -228,9 +229,9 @@ QImage Thumbnailer::fetchThumbnail(PictureEntry &entry, int size)
 	const QString &filename = entry.filename;
 	if (!workingOn.contains(filename)) {
 		workingOn.insert(filename,
-				 QtConcurrent::run(&pool, [this, filename, size]() { processItem(filename, size); }));
+				 QtConcurrent::run(&pool, [this, filename]() { processItem(filename); }));
 	}
-	return QImage(":photo-icon").scaled(size, size, Qt::KeepAspectRatio);
+	return dummyImage;
 }
 
 void Thumbnailer::clearWorkQueue()
@@ -240,3 +241,27 @@ void Thumbnailer::clearWorkQueue()
 		it->cancel();
 	workingOn.clear();
 }
+
+static const int maxZoom = 3;	// Maximum zoom: thrice of standard size
+
+int Thumbnailer::defaultThumbnailSize()
+{
+	return defaultIconMetrics().sz_pic;
+}
+
+int Thumbnailer::maxThumbnailSize()
+{
+	return defaultThumbnailSize() * maxZoom;
+}
+
+int Thumbnailer::thumbnailSize(double zoomLevel)
+{
+	// 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.
+	return static_cast<int>(round(defaultThumbnailSize() * pow(maxZoom, zoomLevel)));
+}
diff --git a/core/imagedownloader.h b/core/imagedownloader.h
index d8e9d2d7d..92edea0b6 100644
--- a/core/imagedownloader.h
+++ b/core/imagedownloader.h
@@ -28,18 +28,23 @@ public:
 	// Schedule a thumbnail for fetching or calculation.
 	// Returns a placehlder thumbnail. The actual thumbnail will be sent
 	// via a signal later.
-	QImage fetchThumbnail(PictureEntry &entry, int size);
+	QImage fetchThumbnail(PictureEntry &entry);
 
 	// If we change dive, clear all unfinished thumbnail creations
 	void clearWorkQueue();
+	static int maxThumbnailSize();
+	static int defaultThumbnailSize();
+	static int thumbnailSize(double zoomLevel);
 signals:
 	void thumbnailChanged(QString filename, QImage thumbnail);
 private:
 	Thumbnailer();
-	void processItem(QString filename, int size);
+	void processItem(QString filename);
 
 	mutable QMutex lock;
 	QThreadPool pool;
+	QImage failImage;		// Shown when image-fetching fails
+	QImage dummyImage;		// Shown before thumbnail is fetched
 
 	QMap<QString,QFuture<void>> workingOn;
 };