skymap.h

/*
    SPDX-FileCopyrightText: 2001 Jason Harris <jharris@30doradus.org>
 
    SPDX-License-Identifier: GPL-2.0-or-later
*/
 
#pragma once
 
#include "config-kstars.h"
 
#include "skymapdrawabstract.h"
#include "printing/legend.h"
#include "skyobjects/skypoint.h"
#include "skyobjects/skyline.h"
#include "nan.h"
 
#include <QGraphicsView>
#include <QtGlobal>
#include <QTimer>
 
class QPainter;
class QPaintDevice;
 
class dms;
class InfoBoxes;
class InfoBoxWidget;
class KSPopupMenu;
class KStarsData;
class Projector;
class SkyObject;
 
#ifdef HAVE_OPENGL
class SkyMapGLDraw;
class SkyMapQDraw;
#endif
 
/**
 * @class SkyMap
 *
 * This is the canvas on which the sky is painted.  It's the main widget for KStars.
 * Contains SkyPoint members for the map's Focus (current central position), Destination
 * (requested central position), FocusPoint (next queued position to be focused),
 * MousePoint (position of mouse cursor), and ClickedPoint (position of last mouse click).
 * Also contains the InfoBoxes for on-screen data display.
 *
 * SkyMap handles most user interaction events (both mouse and keyboard).
 *
 * @short Canvas widget for displaying the sky bitmap; also handles user interaction events.
 *
 * @author Jason Harris
 * @version 1.0
 */
class SkyMap : public QGraphicsView
{
        Q_OBJECT
 
        friend class SkyMapDrawAbstract; // FIXME: SkyMapDrawAbstract requires a lot of access to SkyMap
        friend class SkyMapQDraw;        // FIXME: SkyMapQDraw requires access to computeSkymap
 
    protected:
        /**
            *Constructor.  Read stored settings from KConfig object (focus position,
            *zoom factor, sky color, etc.).  Run initPopupMenus().
            */
        SkyMap();
 
    public:
        static SkyMap *Create();
 
        static SkyMap *Instance();
 
        static bool IsFocused()
        {
            //return (pinstance->focusObject() || pinstance->focusPoint());
            return (pinstance->focusObject());
        }
 
        static bool IsSlewing()
        {
            return pinstance->isSlewing();
        }
 
        /** Destructor (empty) */
        ~SkyMap() override;
 
        enum Projection
        {
            Lambert,
            AzimuthalEquidistant,
            Orthographic,
            Equirectangular,
            Stereographic,
            Gnomonic,
            UnknownProjection
        };
 
        enum Cursor
        {
            NoCursor,
            Cross,
            Circle,
        };
 
        /** @return the angular field of view of the sky map, in degrees.
            *@note it must use either the height or the width of the window to calculate the
            *FOV angle.  It chooses whichever is larger.
            */
        float fov();
 
        /** @short Update object name and coordinates in the Focus InfoBox */
        void showFocusCoords();
 
        /** @brief Update info boxes coordinates */
        void updateInfoBoxes();
 
        /** @short Update the focus position according to current options. */
        void updateFocus();
 
        /** @short Retrieve the Focus point; the position on the sky at the
                *center of the skymap.
                *@return a pointer to the central focus point of the sky map
                */
        SkyPoint *focus()
        {
            return &Focus;
        }
 
        /** @short retrieve the Destination position.
                *
                *The Destination is the point on the sky to which the focus will
                *be moved.
                *
                *@return a pointer to the destination point of the sky map
                */
        SkyPoint *destination()
        {
            return &Destination;
        }
 
        /** @short retrieve the FocusPoint position.
                *
                *The FocusPoint stores the position on the sky that is to be
                *focused next.  This is not exactly the same as the Destination
                *point, because when the Destination is set, it will begin slewing
                *immediately.
                *
                *@return a pointer to the sky point which is to be focused next.
                */
        SkyPoint *focusPoint()
        {
            return &FocusPoint;
        }
 
        /** @short sets the central focus point of the sky map.
                *@param f a pointer to the SkyPoint the map should be centered on
                */
        void setFocus(SkyPoint *f);
 
        /** @short sets the focus point of the skymap, using ra/dec coordinates
                *
                *@note This function behaves essentially like the above function.
                *It differs only in the data types of its arguments.
                *
                *@param ra the new right ascension
                *@param dec the new declination
                */
        void setFocus(const dms &ra, const dms &dec);
 
        /** @short sets the focus point of the sky map, using its alt/az coordinates
                *@param alt the new altitude (actual, without refraction correction)
                *@param az the new azimuth
                */
        void setFocusAltAz(const dms &alt, const dms &az);
 
        /** @short sets the destination point of the sky map.
                *@note setDestination() emits the destinationChanged() SIGNAL,
                *which triggers the SLOT function SkyMap::slewFocus().  This
                *function iteratively steps the Focus point toward Destination,
                *repainting the sky at each step (if Options::useAnimatedSlewing()==true).
                *@param f a pointer to the SkyPoint the map should slew to
                */
        void setDestination(const SkyPoint &f);
 
        /** @short sets the destination point of the skymap, using ra/dec coordinates.
                *
                *@note This function behaves essentially like the above function.
                *It differs only in the data types of its arguments.
                *
                *@param ra the new right ascension
                *@param dec the new declination
                */
        void setDestination(const dms &ra, const dms &dec);
 
        /** @short sets the destination point of the sky map, using its alt/az coordinates.
                *@param alt the new altitude
                *@param az the new azimuth
                *@param altIsRefracted set to true if the altitude supplied is apparent
                */
        void setDestinationAltAz(const dms &alt, const dms &az, bool altIsRefracted);
 
        /** @short set the FocusPoint; the position that is to be the next Destination.
                *@param f a pointer to the FocusPoint SkyPoint.
                */
        void setFocusPoint(SkyPoint *f)
        {
            if (f)
                FocusPoint = *f;
        }
 
        /** @short Retrieve the ClickedPoint position.
                *
                *When the user clicks on a point in the sky map, the sky coordinates of the mouse
                *cursor are stored in the private member ClickedPoint.  This function retrieves
                *a pointer to ClickedPoint.
                *@return a pointer to ClickedPoint, the sky coordinates where the user clicked.
                */
        SkyPoint *clickedPoint()
        {
            return &ClickedPoint;
        }
 
        /**
         * @short Retrieve the mouse pointer position.
         *
         * @return The sky coordinates where the mouse pointer is over.
         */
        SkyPoint *mousePoint()
        {
            return &m_MousePoint;
        }
 
        /** @short Set the ClickedPoint to the skypoint given as an argument.
                *@param f pointer to the new ClickedPoint.
                */
        void setClickedPoint(const SkyPoint *f);
 
        /** @short Retrieve the object nearest to a mouse click event.
                *
                *If the user clicks on the sky map, a pointer to the nearest SkyObject is stored in
                *the private member ClickedObject.  This function returns the ClickedObject pointer,
                *or nullptr if there is no CLickedObject.
                *@return a pointer to the object nearest to a user mouse click.
                */
        SkyObject *clickedObject() const
        {
            return ClickedObject;
        }
 
        /** @short Set the ClickedObject pointer to the argument.
                *@param o pointer to the SkyObject to be assigned as the ClickedObject
                */
        void setClickedObject(SkyObject *o);
 
        /** @short Retrieve the object which is centered in the sky map.
                *
                *If the user centers the sky map on an object (by double-clicking or using the
                *Find Object dialog), a pointer to the "focused" object is stored in
                *the private member FocusObject.  This function returns a pointer to the
                *FocusObject, or nullptr if there is not FocusObject.
                *@return a pointer to the object at the center of the sky map.
                */
        SkyObject *focusObject() const
        {
            return FocusObject;
        }
 
        /** @short Set the FocusObject pointer to the argument.
                *@param o pointer to the SkyObject to be assigned as the FocusObject
                */
        void setFocusObject(SkyObject *o);
 
        /** @short Call to set up the projector before a draw cycle. */
        void setupProjector();
 
        /** @ Set zoom factor.
              *@param factor zoom factor
              */
        void setZoomFactor(double factor);
 
        bool isSlewing() const;
 
        // NOTE: This method is draw-backend independent.
        /** @short update the geometry of the angle ruler. */
        void updateAngleRuler();
 
        /** @return true if the object currently has a user label attached.
                *@note this function only checks for a label explicitly added to the object
                *with the right-click popup menu; other kinds of labels are not detected by
                *this function.
                *@param o pointer to the sky object to be tested for a User label.
                */
        bool isObjectLabeled(SkyObject *o);
 
        /*@*@short Convenience function for shutting off tracking mode.  Just calls KStars::slotTrack().
                */
        void stopTracking();
 
        /** Get the current projector.
                @return a pointer to the current projector. */
        inline const Projector *projector() const
        {
            return m_proj;
        }
 
        // NOTE: These dynamic casts must not segfault. If they do, it's good because we know that there is a problem.
        /**
             *@short Proxy method for SkyMapDrawAbstract::exportSkyImage()
             */
        inline void exportSkyImage(QPaintDevice *pd, bool scale = false)
        {
            dynamic_cast<SkyMapDrawAbstract *>(m_SkyMapDraw)->exportSkyImage(pd, scale);
        }
 
        inline void exportSkyImage(SkyQPainter *painter, bool scale = false)
        {
            dynamic_cast<SkyMapDrawAbstract *>(m_SkyMapDraw)->exportSkyImage(painter, scale);
        }
 
        SkyMapDrawAbstract *getSkyMapDrawAbstract()
        {
            return dynamic_cast<SkyMapDrawAbstract *>(m_SkyMapDraw);
        }
 
        /**
             *@short Proxy method for SkyMapDrawAbstract::drawObjectLabels()
             */
        inline void drawObjectLabels(QList<SkyObject *> &labelObjects)
        {
            dynamic_cast<SkyMapDrawAbstract *>(m_SkyMapDraw)->drawObjectLabels(labelObjects);
        }
 
        void setPreviewLegend(bool preview)
        {
            m_previewLegend = preview;
        }
 
        void setLegend(const Legend &legend)
        {
            m_legend = legend;
        }
 
        bool isInObjectPointingMode() const
        {
            return m_objPointingMode;
        }
 
        void setObjectPointingMode(bool enabled)
        {
            m_objPointingMode = enabled;
        }
 
        void setFovCaptureMode(bool enabled)
        {
            m_fovCaptureMode = enabled;
        }
 
        bool isInFovCaptureMode() const
        {
            return m_fovCaptureMode;
        }
 
        /** @short Sets the shape of the default mouse cursor. */
        void setMouseCursorShape(Cursor type);
 
        SkyPoint getCenterPoint();
 
        /** @short Sets the extra rotation applied to FOV symbols (before correction) to the given angle. */
        void setExtraFovRotation(double angle);
 
        /** @short Gets the extra rotation applied to FOV symbols. */
        double extraFovRotation() const {
            return m_fovExtraRotation;
        }
 
    public slots:
        /** Recalculates the positions of objects in the sky, and then repaints the sky map.
             * If the positions don't need to be recalculated, use update() instead of forceUpdate().
             * This saves a lot of CPU time.
             * @param now if true, paintEvent() is run immediately.  Otherwise, it is added to the event queue
             */
        void forceUpdate(bool now = false);
 
        /** @short Convenience function; simply calls forceUpdate(true).
             * @see forceUpdate()
             */
        void forceUpdateNow()
        {
            forceUpdate(true);
        }
 
        /**
             * @short Update the focus point and call forceUpdate()
             * @param now is passed on to forceUpdate()
             */
        void slotUpdateSky(bool now);
 
        /** Toggle visibility of geo infobox */
        void slotToggleGeoBox(bool);
 
        /** Toggle visibility of focus infobox */
        void slotToggleFocusBox(bool);
 
        /** Toggle visibility of time infobox */
        void slotToggleTimeBox(bool);
 
        /** Toggle visibility of all infoboxes */
        void slotToggleInfoboxes(bool);
 
        /** Sets the base sky rotation (before correction) to the given angle */
        void slotSetSkyRotation(double angle);
 
        /** Step the Focus point toward the Destination point.  Do this iteratively, redrawing the Sky
             * Map after each step, until the Focus point is within 1 step of the Destination point.
             * For the final step, snap directly to Destination, and redraw the map.
             */
        void slewFocus();
 
        /** @short Center the display at the point ClickedPoint.
             *
             * The essential part of the function is to simply set the Destination point, which will emit
             * the destinationChanged() SIGNAL, which triggers the slewFocus() SLOT.  Additionally, this
             * function performs some bookkeeping tasks, such updating whether we are tracking the new
             * object/position, adding a Planet Trail if required, etc.
             *
             * @see destinationChanged()
             * @see slewFocus()
             */
        void slotCenter();
 
        /** @short Popup menu function: Display 1st-Generation DSS image with the Image Viewer.
             * @note the URL is generated using the coordinates of ClickedPoint.
             */
        void slotDSS();
 
        /** @short Popup menu function: Display Sloan Digital Sky Survey image with the Image Viewer.
             * @note the URL is generated using the coordinates of ClickedPoint.
             */
        void slotSDSS();
 
        /**
         * @brief slotCopyCoordinates Copies J2000 and JNow equatorial coordinates to the clipboard in addition to horizontal coords.
         */
        void slotCopyCoordinates();
 
        /**
         * @brief slotCopyTLE Copy satellite TLE to clipboard.
         */
        void slotCopyTLE();
 
        /** @short Popup menu function: Show webpage about ClickedObject
             * (only available for some objects).
             */
        void slotInfo();
 
        /** @short Popup menu function: Show image of ClickedObject
             * (only available for some objects).
             */
        void slotImage();
 
        /** @short Popup menu function: Show the Detailed Information window for ClickedObject. */
        void slotDetail();
 
        /** Add ClickedObject to KStarsData::ObjLabelList, which stores pointers to SkyObjects which
             * have User Labels attached.
             */
        void slotAddObjectLabel();
 
        /** Remove ClickedObject from KStarsData::ObjLabelList, which stores pointers to SkyObjects which
             * have User Labels attached.
             */
        void slotRemoveObjectLabel();
 
        /** Remove custom object from internet search in the local catalog */
        void slotRemoveCustomObject();
 
        /** @short Add a Planet Trail to ClickedObject.
             * @note Trails are added simply by calling KSPlanetBase::addToTrail() to add the first point.
             * as long as the trail is not empty, new points will be automatically appended to it.
             * @note if ClickedObject is not a Solar System body, this function does nothing.
             * @see KSPlanetBase::addToTrail()
             */
        void slotAddPlanetTrail();
 
        /** @short Remove the PlanetTrail from ClickedObject.
             * @note The Trail is removed by simply calling KSPlanetBase::clearTrail().  As long as
             * the trail is empty, no new points will be automatically appended.
             * @see KSPlanetBase::clearTrail()
             */
        void slotRemovePlanetTrail();
 
        /** @short Render a fading text label on the screen to flash information */
        void slotDisplayFadingText(const QString &text);
 
        /** Checks whether the timestep exceeds a threshold value.  If so, sets
             * ClockSlewing=true and sets the SimClock to ManualMode.
             */
        void slotClockSlewing();
 
        /** Enables the angular distance measuring mode. It saves the first
             * position of the ruler in a SkyPoint. It makes difference between
             * having clicked on the skymap and not having done so
             * \note This method is draw-backend independent.
            */
        void slotBeginAngularDistance();
 
        void slotBeginStarHop(); // TODO: Add docs
 
        /** Computes the angular distance, prints the result in the status
             * bar and disables the angular distance measuring mode
             * If the user has clicked on the map the status bar shows the
             * name of the clicked object plus the angular distance. If
             * the user did not clicked on the map, just pressed ], only
             * the angular distance is printed
             * \note This method is draw-backend independent.
            */
        void slotEndRulerMode();
 
        /** Disables the angular distance measuring mode. Nothing is printed
             * in the status bar */
        void slotCancelRulerMode();
 
        /** @short Open Flag Manager window with clickedObject() RA and Dec entered.
              */
        void slotAddFlag();
 
        /** @short Open Flag Manager window with RA and Dec entered.
              */
        void slotAddFlagRaw();
 
        /** @short Open Flag Manager window with selected flag focused and ready to edit.
              *@param flagIdx index of flag to be edited.
              */
        void slotEditFlag(int flagIdx);
 
        /** @short Delete selected flag.
              *@param flagIdx index of flag to be deleted.
              */
        void slotDeleteFlag(int flagIdx);
 
#ifdef HAVE_OPENGL
        void slotToggleGL();
#endif
 
        /** Run Xplanet Viewer to display images of the planets*/
        void slotStartXplanetViewer();
 
        /** Zoom in one step. */
        void slotZoomIn();
 
        /** Zoom out one step. */
        void slotZoomOut();
 
        /** Set default zoom. */
        void slotZoomDefault();
 
        /** Object pointing for Printing Wizard done */
        void slotObjectSelected();
 
        void slotCancelLegendPreviewMode();
 
        void slotFinishFovCaptureMode();
 
        void slotCaptureFov();
 
    signals:
        /** Emitted by setDestination(), and connected to slewFocus().  Whenever the Destination
             * point is changed, slewFocus() will iteratively step the Focus toward Destination
             * until it is reached.
             * @see SkyMap::setDestination()
             * @see SkyMap::slewFocus()
             */
        void destinationChanged();
 
        /** Emitted when zoom level is changed. */
        void zoomChanged();
 
        /** Emitted when current object changed. */
        void objectChanged(SkyObject *);
 
        /** Emitted when pointing changed. (At least should) */
        void positionChanged(SkyPoint *);
 
        /** Emitted when position under mouse changed. */
        void mousePointChanged(SkyPoint *);
 
        /** Emitted when a position is clicked */
        void positionClicked(SkyPoint *);
 
        /** Emitted when a position is clicked */
        void objectClicked(SkyObject *);
 
        /** Emitted when a sky object is removed from the database */
        void removeSkyObject(SkyObject *object);
 
        /** Emitter when mosaic center is dragged in the sky map */
        void mosaicCenterChanged(dms dRA, dms dDE);
 
        void updateQueued();
 
    protected:
        bool event(QEvent *event) override;
 
        /** Process keystrokes:
             * @li arrow keys  Slew the map
             * @li +/- keys  Zoom in and out
             * @li <i>Space</i>  Toggle between Horizontal and Equatorial coordinate systems
             * @li 0-9  Go to a major Solar System body (0=Sun; 1-9 are the major planets, except 3=Moon)
             * @li [  Place starting point for measuring an angular distance
             * @li ]  End point for Angular Distance; display measurement.
             * @li <i>Escape</i>  Cancel Angular measurement
             * @li ,/<  Step backward one time step
             * @li ./>  Step forward one time step
             */
        void keyPressEvent(QKeyEvent *e) override;
 
        /** When keyRelease is triggered, just set the "slewing" flag to false,
             * and update the display (to draw objects that are hidden when slewing==true). */
        void keyReleaseEvent(QKeyEvent *e) override;
 
        /** Determine RA, Dec coordinates of clicked location.  Find the SkyObject
             * which is nearest to the clicked location.
             *
             * If left-clicked: Set set mouseButtonDown==true, slewing==true; display
             * nearest object name in status bar.
             * If right-clicked: display popup menu appropriate for nearest object.
             */
        void mousePressEvent(QMouseEvent *e) override;
 
        /** set mouseButtonDown==false, slewing==false */
        void mouseReleaseEvent(QMouseEvent *e) override;
 
        /** Center SkyMap at double-clicked location  */
        void mouseDoubleClickEvent(QMouseEvent *e) override;
 
        /** This function does several different things depending on the state of the program:
             * @li If Angle-measurement mode is active, update the end-ruler point to the mouse cursor,
             *     and continue this function.
             * @li If we are defining a ZoomBox, update the ZoomBox rectangle, redraw the screen,
             *     and return.
             * @li If dragging the mouse in the map, update focus such that RA, Dec under the mouse
             *     cursor remains constant.
             * @li If just moving the mouse, simply update the curso coordinates in the status bar.
             */
        void mouseMoveEvent(QMouseEvent *e) override;
 
        /** Zoom in and out with the mouse wheel. */
        void wheelEvent(QWheelEvent *e) override;
 
        /** If the skymap will be resized, the sky must be new computed. So this
             * function calls explicitly new computing of the skymap.
             */
        void resizeEvent(QResizeEvent *) override;
 
    private slots:
        /** @short display tooltip for object under cursor. It's called by m_HoverTimer.
             *  if mouse didn't moved for last HOVER_INTERVAL milliseconds.
             */
        void slotTransientLabel();
 
        /** Set the shape of mouse cursor to a cross with 4 arrows. */
        void setMouseMoveCursor();
 
        /** Set the shape of mouse cursor to an open hand. */
        void setMouseDragCursor();
 
    private:
 
        /** @short Sets the shape of the mouse cursor to a magnifying glass. */
        void setZoomMouseCursor();
 
        /** @short Sets the shape of the mouse cursor to a rotation symbol. */
        void setRotationMouseCursor();
 
        /** @short Sets the shape of the mouse cursor to a fov rotation symbol. */
        void setFovRotationMouseCursor();
 
        /** Calculate the zoom factor for the given keyboard modifier
             */
        double zoomFactor(const int modifier);
 
        /** calculate the magnitude factor (1, .5, .2, or .1) for the given
             * keyboard modifier.
             */
        double magFactor(const int modifier);
 
        /** Decrease the magnitude limit by a step size determined by the
             * keyboard modifier.
             * @param modifier
             */
        void decMagLimit(const int modifier);
 
        /** Increase the magnitude limit by a step size determined by the
            * keyboard modifier.
            * @param modifier
            */
        void incMagLimit(const int modifier);
 
        /** Convenience routine to either zoom in or increase mag limit
             * depending on the Alt modifier.  The Shift and Control modifiers
             * will adjust the size of the zoom or the mag step.
             * @param modifier
             */
        void zoomInOrMagStep(const int modifier);
 
        /** Convenience routine to either zoom out or decrease mag limit
             * depending on the Alt modifier.  The Shift and Control modifiers
             * will adjust the size of the zoom or the mag step.
             * @param modifier
             */
        void zoomOutOrMagStep(const int modifier);
 
        void beginRulerMode(bool starHopRuler); // TODO: Add docs
 
        /**
         * Determine the rotation angle of the SkyMap
         *
         * This is simply Options::skyRotation() if the erect observer
         * correction is not applicable, but otherwise it is
         * determined by adding a correction amount dependent on the
         * focus of the sky map
         */
        dms determineSkyRotation();
 
        /**
         * @short Strart xplanet.
         * @param outputFile Output file path.
         */
        void startXplanet(const QString &outputFile = "");
 
        bool mouseButtonDown { false };
        bool midMouseButtonDown { false };
        /// True if mouseMoveEvent; needed by setMouseMoveCursor
        bool mouseMoveCursor { false };
        bool mouseDragCursor { false };
        bool slewing { false };
        bool clockSlewing { false };
        //if false only old pixmap will repainted with bitBlt(), this
        // saves a lot of cpu usage
        bool computeSkymap { false };
        // True if we are either looking for angular distance or star hopping directions
        bool rulerMode { false };
        // True only if we are looking for star hopping directions. If
        // false while rulerMode is true, it means we are measuring angular
        // distance. FIXME: Find a better way to do this
        bool starHopDefineMode { false };
        double y0;
 
        QPoint rotationStart;
        dms rotationStartAngle;
 
        QPoint fovRotationStart;
        dms fovRotationStartAngle;
 
        double m_Scale;
 
        KStarsData *data { nullptr };
        KSPopupMenu *pmenu { nullptr };
 
        /// Coordinates of point under cursor. It's update in function mouseMoveEvent
        SkyPoint m_MousePoint;
 
        // A copy of m_MousePoint, copied when the mouse is pressed.
        SkyPoint m_MousePointPressed;
 
        SkyPoint Focus, ClickedPoint, FocusPoint, Destination;
        SkyObject *ClickedObject { nullptr };
        SkyObject *FocusObject { nullptr };
 
        Projector *m_proj { nullptr };
 
        SkyLine AngularRuler; //The line for measuring angles in the map
        QRect ZoomRect;       //The manual-focus circle.
 
        // Mouse should not move for that interval to display tooltip
        static const int HOVER_INTERVAL = 500;
        // Timer for tooltips
        QTimer m_HoverTimer;
 
        // InfoBoxes. Used in destructor to save state
        InfoBoxWidget *m_timeBox { nullptr };
        InfoBoxWidget *m_geoBox { nullptr };
        InfoBoxWidget *m_objBox { nullptr };
        InfoBoxes *m_iboxes { nullptr };
 
        // legend
        bool m_previewLegend { false };
        Legend m_legend;
 
        bool m_objPointingMode { false };
        bool m_fovCaptureMode { false };
        bool m_touchMode { false };
        bool m_pinchMode { false };
        bool m_tapAndHoldMode { false };
        qreal m_pinchScale { 0.0 };
 
        QWidget *m_SkyMapDraw { nullptr }; // Can be dynamic_cast<> to SkyMapDrawAbstract
 
        // NOTE: These are pointers to the individual widgets
#ifdef HAVE_OPENGL
        SkyMapQDraw *m_SkyMapQDraw { nullptr };
        SkyMapGLDraw *m_SkyMapGLDraw { nullptr };
#endif
 
        static SkyMap *pinstance;
        /// Good to keep the original ruler start-point for purposes of dynamic_cast
        const SkyPoint *m_rulerStartPoint { nullptr };
 
        // Extra rotation applied to FOV symbols.
        double m_fovExtraRotation { 0.0 };
};