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>

desktop-widgets/divepicturewidget.cpp

@@ -59,3 +59,17 @@ void DivePictureWidget::mousePressEvent(QMouseEvent *event)
 		QListView::mousePressEvent(event);
 	}
 }
+
+void DivePictureWidget::wheelEvent(QWheelEvent *event)
+{
+	if (event->modifiers() == Qt::ControlModifier) {
+		// Angle delta is given in eighth parts of a degree. A classical mouse
+		// wheel click is 15 degrees. Each click should correspond to one zoom step.
+		// Therefore, divide by 15*8=120. To also support touch pads and finer-grained
+		// mouse wheels, take care to always round away from zero.
+		int delta = event->angleDelta().y();
+		int carry = delta > 0 ? 119 : -119;
+		emit zoomLevelChanged((delta + carry) / 120);
+	} else
+		QListView::wheelEvent(event);
+}

desktop-widgets/divepicturewidget.h

@@ -14,9 +14,11 @@ public:
 protected:
 	void mouseDoubleClickEvent(QMouseEvent *event) Q_DECL_OVERRIDE;
 	void mousePressEvent(QMouseEvent *event) Q_DECL_OVERRIDE;
+	void wheelEvent(QWheelEvent *event) Q_DECL_OVERRIDE;
 
 signals:
 	void photoDoubleClicked(const QString filePath);
+	void zoomLevelChanged(int delta);
 };
 
 class DivePictureThumbnailThread : public QThread {

desktop-widgets/tab-widgets/TabDivePhotos.cpp

@@ -29,6 +29,10 @@ TabDivePhotos::TabDivePhotos(QWidget *parent)
 			QDesktopServices::openUrl(QUrl::fromLocalFile(path));
 		}
 	);
+	connect(ui->photosView, &DivePictureWidget::zoomLevelChanged,
+		this, &TabDivePhotos::changeZoomLevel);
+	connect(ui->zoomSlider, &QAbstractSlider::valueChanged,
+		DivePictureModel::instance(), &DivePictureModel::setZoomLevel);
 }
 
 TabDivePhotos::~TabDivePhotos()
@@ -98,3 +102,8 @@ void TabDivePhotos::updateData()
 	divePictureModel->updateDivePictures();
 }
 
+void TabDivePhotos::changeZoomLevel(int delta)
+{
+	// We count on QSlider doing bound checks
+	ui->zoomSlider->setValue(ui->zoomSlider->value() + delta);
+}

desktop-widgets/tab-widgets/TabDivePhotos.h

@@ -26,6 +26,7 @@ private slots:
 	void addPhotosFromURL();
 	void removeAllPhotos();
 	void removeSelectedPhotos();
+	void changeZoomLevel(int delta);
 
 private:
 	Ui::TabDivePhotos *ui;

desktop-widgets/tab-widgets/TabDivePhotos.ui

@@ -21,6 +21,42 @@
      </property>
     </widget>
    </item>
+   <item>
+    <layout class="QHBoxLayout" name="zoomLayout">
+     <item>
+      <widget class="QLabel" name="zoomLabel">
+       <property name="text">
+        <string>Zoom level</string>
+       </property>
+      </widget>
+     </item>
+     <item>
+      <widget class="QSlider" name="zoomSlider">
+       <property name="minimum">
+        <number>-10</number>
+       </property>
+       <property name="maximum">
+        <number>10</number>
+       </property>
+       <property name="singleStep">
+        <number>1</number>
+       </property>
+       <property name="pageStep">
+        <number>1</number>
+       </property>
+       <property name="orientation">
+        <enum>Qt::Horizontal</enum>
+       </property>
+       <property name="tickPosition">
+        <enum>QSlider::TicksBelow</enum>
+       </property>
+       <property name="tickInterval">
+        <number>1</number>
+       </property>
+      </widget>
+     </item>
+    </layout>
+   </item>
   </layout>
  </widget>
  <customwidgets>

profile-widget/profilewidget2.cpp

@@ -2007,7 +2007,7 @@ void ProfileWidget2::plotPictures()
 		if (!offsetSeconds)
 			continue;
 		DivePictureItem *item = new DivePictureItem();
-		item->setPixmap(m->index(i, 0).data(Qt::DecorationRole).value<QPixmap>());
+		item->setPixmap(m->index(i, 0).data(Qt::UserRole).value<QPixmap>());
 		item->setFileUrl(m->index(i, 1).data().toString());
 		// let's put the picture at the correct time, but at a fixed "depth" on the profile
 		// not sure this is ideal, but it seems to look right.

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;
+	return thumbnailCache.value(entry.filename);
 }
-	l.unlock();
 
-	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;

qt-models/divepicturemodel.h

@@ -10,6 +10,7 @@ struct PictureEntry {
 	struct picture *picture;
 	QString filename;
 	QImage image;
+	QImage imageProfile;	// For the profile widget keep a copy of a constant sized image
 	int offsetSeconds;
 };
 
@@ -24,9 +25,13 @@ public:
 	void updateDivePicturesWhenDone(QList<QFuture<void>>);
 	void removePicture(const QString& fileUrl, bool last);
 	int rowDDStart, rowDDEnd;
+public slots:
+	void setZoomLevel(int level);
 private:
 	DivePictureModel();
 	QList<PictureEntry> pictures;
+	double zoomLevel;	// -1.0: minimum, 0.0: standard, 1.0: maximum
+	void updateThumbnails();
 };
 
 #endif