Faster graph zoom by using a snapshot-preview (#1728)

* Faster graph zoom by using a snapshot-preview

* Added "Fast Zooming..." menu option

---------

Co-authored-by: matlabbe <matlabbe@gmail.com>

guilib/include/rtabmap/gui/GraphViewer.h

@@ -33,6 +33,8 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <QGraphicsView>
 #include <QtCore/QMap>
 #include <QtCore/QSettings>
+#include <QTimer>
+#include <QGraphicsPixmapItem>
 #include <rtabmap/core/Link.h>
 #include <rtabmap/core/GPS.h>
 #include <opencv2/opencv.hpp>
@@ -130,6 +132,7 @@ public:
 	bool isOrientationENU() const;
 	ViewPlane getViewPlane() const;
 	bool isEnsureFrameVisible() const;
+	int getFastZoomMinNodes() const;
 
 	// setters
 	void setWorkingDirectory(const QString & path);
@@ -170,6 +173,7 @@ public:
 	void setOrientationENU(bool enabled);
 	void setViewPlane(ViewPlane plane);
 	void setEnsureFrameVisible(bool visible);
+	void setFastZoomMinNodes(int value);
 
 Q_SIGNALS:
 	void configChanged();
@@ -184,11 +188,14 @@ protected:
 	virtual void wheelEvent ( QWheelEvent * event );
 	virtual void mouseMoveEvent(QMouseEvent * event);
 	virtual void mousePressEvent(QMouseEvent * event);
+	virtual void mouseReleaseEvent(QMouseEvent * event);
 	virtual void contextMenuEvent(QContextMenuEvent * event);
 
 private:
 	void setupGraphicsScene();
-
+	void startZoomOverlay();
+	void updateZoomOverlay();
+	void stopZoomOverlay();
 private:
 	QString _workingDirectory;
 	QColor _nodeColor;
@@ -248,6 +255,11 @@ private:
 	ViewPlane _viewPlane;
 	bool _ensureFrameVisible;
 	QPoint _previousMousePos;
+	QPoint _initialMousePos;
+	QTimer _zoomDebounceTimer;
+	QGraphicsPixmapItem * _zoomOverlayItem;
+	bool _zoomOverlayActive;
+	int _fastZoomMinNodes;
 };
 
 } /* namespace rtabmap */

guilib/src/GraphViewer.cpp

@@ -32,6 +32,7 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <QGraphicsScene>
 #include <QGraphicsEllipseItem>
 #include <QGraphicsRectItem>
+#include <QGraphicsPixmapItem>
 #include <QtGui/QWheelEvent>
 #include <QGraphicsSceneHoverEvent>
 #include <QMenu>
@@ -341,10 +342,18 @@ GraphViewer::GraphViewer(QWidget * parent) :
 		_orientationENU(false),
 		_mouseTracking(false),
 		_viewPlane(XY),
-		_ensureFrameVisible(true)
+		_ensureFrameVisible(true),
+		_previousMousePos(-1,-1),
+		_initialMousePos(-1,-1),
+		_zoomDebounceTimer(this),
+		_zoomOverlayItem(0),
+		_zoomOverlayActive(false),
+		_fastZoomMinNodes(0)
 {
 	this->setDragMode(QGraphicsView::ScrollHandDrag);
 	_workingDirectory = QDir::homePath();
+	_zoomDebounceTimer.setSingleShot(true);
+	connect(&_zoomDebounceTimer, &QTimer::timeout, this, &GraphViewer::stopZoomOverlay);
 
 	setupGraphicsScene();
 
@@ -355,6 +364,9 @@ GraphViewer::GraphViewer(QWidget * parent) :
 	this->restoreDefaults();
 
 	this->fitInView(this->sceneRect(), Qt::KeepAspectRatio);
+	
+	setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
+    setResizeAnchor(QGraphicsView::AnchorUnderMouse);
 }
 
 GraphViewer::~GraphViewer()
@@ -363,11 +375,20 @@ GraphViewer::~GraphViewer()
 
 void GraphViewer::setupGraphicsScene()
 {
+	_zoomDebounceTimer.stop();
+	_zoomOverlayActive = false;
+	_zoomOverlayItem = 0;
 	if(this->scene())
 	{
 		delete this->scene();
 	}
 	this->setScene(new QGraphicsScene(this));
+	_zoomOverlayItem = this->scene()->addPixmap(QPixmap());
+	_zoomOverlayItem->setZValue(1000000);
+	_zoomOverlayItem->setVisible(false);
+	_zoomOverlayItem->setAcceptedMouseButtons(Qt::NoButton);
+	_zoomOverlayItem->setAcceptHoverEvents(false);
+	
 	_world = (QGraphicsItem *)this->scene()->addEllipse(QRectF(-0.0001,-0.0001,0.0001,0.0001));
 	_root = (QGraphicsItem *)this->scene()->addEllipse(QRectF(-0.0001,-0.0001,0.0001,0.0001));
 	_root->setParentItem(_world);
@@ -507,6 +528,62 @@ void GraphViewer::setupGraphicsScene()
 
 }
 
+void GraphViewer::startZoomOverlay()
+{
+	if(_fastZoomMinNodes==0 || _nodeItems.size() < _fastZoomMinNodes)
+	{
+		return;
+	}
+
+	if(_zoomOverlayActive || !_zoomOverlayItem)
+ 	{
+ 		return;
+ 	}
+ 
+	const QRect viewportRect = this->viewport()->rect();
+	if(viewportRect.isEmpty())
+ 	{
+ 		return;
+ 	}
+
+	const QPixmap snapshot = this->viewport()->grab();
+	if(snapshot.isNull())
+	{
+		return;
+	}
+
+	const QRectF sourceRect = this->mapToScene(viewportRect).boundingRect();
+	const qreal sx = sourceRect.width() / qreal(snapshot.width());
+	const qreal sy = sourceRect.height() / qreal(snapshot.height());
+
+	_zoomOverlayItem->setPixmap(snapshot);
+	_zoomOverlayItem->setTransform(QTransform::fromScale(sx, sy));
+	_zoomOverlayItem->setPos(sourceRect.topLeft());
+	_zoomOverlayItem->show();
+ 	_world->setVisible(false);
+ 	_zoomOverlayActive = true;
+}
+
+void GraphViewer::stopZoomOverlay()
+{
+	_zoomDebounceTimer.stop();
+	if(!_zoomOverlayActive)
+	{
+		return;
+	}
+
+	_zoomOverlayActive = false;
+	if(_zoomOverlayItem)
+	{
+		_zoomOverlayItem->hide();
+	}
+	if(_world)
+	{
+		_world->setVisible(true);
+	}
+	this->viewport()->update();
+}
+
 void GraphViewer::setWorldMapRotation(const float & theta)
 {
 	_worldMapRotation = theta;
@@ -1432,6 +1509,7 @@ void GraphViewer::clearNodeColorByValue()
 
 void GraphViewer::clearAll()
 {
+	stopZoomOverlay();
 	clearMap();
 	clearGraph();
 
@@ -1489,6 +1567,7 @@ void GraphViewer::saveSettings(QSettings & settings, const QString & group) cons
 	settings.setValue("orientation_ENU", this->isOrientationENU());
 	settings.setValue("view_plane", (int)this->getViewPlane());
 	settings.setValue("ensure_frame_visible", (int)this->isEnsureFrameVisible());
+	settings.setValue("fast_zoom_min_nodes", this->getFastZoomMinNodes());
 	if(!group.isEmpty())
 	{
 		settings.endGroup();
@@ -1540,6 +1619,7 @@ void GraphViewer::loadSettings(QSettings & settings, const QString & group)
 	this->setOrientationENU(settings.value("orientation_ENU", this->isOrientationENU()).toBool());
 	this->setViewPlane((ViewPlane)settings.value("view_plane", (int)this->getViewPlane()).toInt());
 	this->setEnsureFrameVisible(settings.value("ensure_frame_visible", this->isEnsureFrameVisible()).toBool());
+	this->setFastZoomMinNodes(settings.value("fast_zoom_min_nodes", this->getFastZoomMinNodes()).toInt());
 	if(!group.isEmpty())
 	{
 		settings.endGroup();
@@ -1602,6 +1682,10 @@ bool GraphViewer::isEnsureFrameVisible() const
 {
 	return _ensureFrameVisible;
 }
+int GraphViewer::getFastZoomMinNodes() const
+{
+	return _fastZoomMinNodes;
+}
 
 void GraphViewer::setWorkingDirectory(const QString & path)
 {
@@ -1967,6 +2051,11 @@ void GraphViewer::setEnsureFrameVisible(bool visible)
 	_ensureFrameVisible = visible;
 }
 
+void GraphViewer::setFastZoomMinNodes(int value)
+{
+	_fastZoomMinNodes = value;
+}
+
 
 void GraphViewer::restoreDefaults()
 {
@@ -1997,18 +2086,26 @@ void GraphViewer::restoreDefaults()
 	setGlobalPathVisible(true);
 	setLocalPathVisible(true);
 	setGtGraphVisible(true);
+	setFastZoomMinNodes(0);
 }
 
-void GraphViewer::wheelEvent ( QWheelEvent * event )
+void GraphViewer::wheelEvent(QWheelEvent * event)
 {
-	if(event->angleDelta().y() < 0)
+	if(event->angleDelta().y() == 0)
 	{
-		this->scale(0.95, 0.95);
-	}
-	else
-	{
-		this->scale(1.05, 1.05);
+		event->ignore();
+		return;
 	}
+
+	// Start buffering zoom interaction with a raster snapshot.
+	startZoomOverlay();
+	
+	const qreal factor = event->angleDelta().y() < 0 ? 0.95 : 1.05;
+	this->scale(factor, factor);
+
+	// When wheel stops for 400 ms, restore the real scene and let it redraw once.
+	_zoomDebounceTimer.start(400);
+	event->accept();
 }
 
 void GraphViewer::mouseMoveEvent(QMouseEvent * event)
@@ -2029,14 +2126,16 @@ void GraphViewer::mouseMoveEvent(QMouseEvent * event)
 	if (event->modifiers() & (Qt::ShiftModifier | Qt::ControlModifier) && event->buttons() & Qt::LeftButton) {
 		// same modifiers than 3D view, change zoom
 		if(_previousMousePos.y()!=0) {
-			if(event->pos().y() - _previousMousePos.y() > 0)
-			{
-				this->scale(0.98, 0.98);
-			}
-			else
-			{
-				this->scale(1.02, 1.02);
-			}
+			qreal factor = (event->pos().y() - _previousMousePos.y() > 0) ? 0.98 : 1.02;
+			
+			QGraphicsView::ViewportAnchor oldAnchor = this->transformationAnchor();
+			this->setTransformationAnchor(QGraphicsView::NoAnchor);
+			QPointF scenePointBefore = this->mapToScene(_initialMousePos);
+			this->scale(factor, factor);
+			QPointF scenePointAfter = this->mapToScene(_initialMousePos);
+			QPointF delta = scenePointAfter - scenePointBefore;
+			this->translate(delta.x(), delta.y());
+			this->setTransformationAnchor(oldAnchor);
 		}
 		_previousMousePos = event->pos();
 		return;
@@ -2047,11 +2146,21 @@ void GraphViewer::mouseMoveEvent(QMouseEvent * event)
 
 void GraphViewer::mousePressEvent(QMouseEvent * event)
 {
-	QGraphicsItem *item = this->scene()->itemAt(mapToScene(event->pos()), QTransform());
+	if((event->button() == Qt::LeftButton) &&
+	   (event->modifiers() & (Qt::ShiftModifier | Qt::ControlModifier)))
+	{
+		startZoomOverlay();
+		_previousMousePos = event->pos();
+		_initialMousePos = event->pos();
+		event->accept();
+		return;
+	}
+
+	QGraphicsItem * item = this->scene()->itemAt(mapToScene(event->pos()), QTransform());
 	if(item)
 	{
-		NodeItem *nodeItem = qgraphicsitem_cast<NodeItem*>(item);
-		LinkItem *linkItem = qgraphicsitem_cast<LinkItem*>(item);
+		NodeItem * nodeItem = qgraphicsitem_cast<NodeItem*>(item);
+		LinkItem * linkItem = qgraphicsitem_cast<LinkItem*>(item);
 		if(nodeItem && nodeItem->parentItem() == _graphRoot && nodeItem->id() != 0)
 		{
 			Q_EMIT nodeSelected(nodeItem->id());
@@ -2071,6 +2180,19 @@ void GraphViewer::mousePressEvent(QMouseEvent * event)
 	}
 }
 
+void GraphViewer::mouseReleaseEvent(QMouseEvent * event)
+{
+	_previousMousePos = QPoint(-1, -1);
+	_initialMousePos = QPoint(-1, -1);
+
+	if(_zoomOverlayActive)
+	{
+		stopZoomOverlay();
+	}
+
+	QGraphicsView::mouseReleaseEvent(event);
+}
+
 QIcon createIcon(const QColor & color)
 {
 	QPixmap pixmap(50, 50);
@@ -2167,6 +2289,7 @@ void GraphViewer::contextMenuEvent(QContextMenuEvent * event)
 	QAction * aShowHideOdomCacheOverlay;
 	QAction * aOrientationENU;
 	QAction * aMouseTracking;
+	QAction * aFastZooming;
 	QAction * aViewPlaneXY;
 	QAction * aViewPlaneXZ;
 	QAction * aViewPlaneYZ;
@@ -2269,6 +2392,7 @@ void GraphViewer::contextMenuEvent(QContextMenuEvent * event)
 	aMouseTracking->setCheckable(true);
 	aMouseTracking->setChecked(_mouseTracking);
 	aMouseTracking->setEnabled(_viewPlane == XY);
+	aFastZooming = menu.addAction(tr("Fast Zooming..."));
 	aShowHideGraph->setEnabled(_viewPlane == XY);
 	aShowHideGlobalPath->setEnabled(_globalPathLinkItems.size());
 	aShowHideLocalPath->setEnabled(_localPathLinkItems.size());
@@ -2714,6 +2838,15 @@ void GraphViewer::contextMenuEvent(QContextMenuEvent * event)
 	{
 		_mouseTracking = aMouseTracking->isChecked();
 	}
+	else if(r == aFastZooming)
+	{
+		bool ok;
+		double value = QInputDialog::getInt(this, tr("Fast Zooming"), tr("Minimum number of nodes to raster the graph\nwhile zooming (0=disabled):"), _fastZoomMinNodes, 0, 2147483647, 100, &ok);
+		if(ok)
+		{
+			setFastZoomMinNodes(value);
+		}
+	}
 	else if(r == aViewPlaneXY)
 	{
 		this->setViewPlane(XY);