QGraphicsItem - QGraphicsScene - QGraphicsView

1.QGraphicsItem -- 是个基类

class Q_WIDGETS_EXPORT QGraphicsItem
{
public:
    enum GraphicsItemFlag {
        ItemIsMovable = 0x1,
        ItemIsSelectable = 0x2,
        ItemIsFocusable = 0x4,
        ItemClipsToShape = 0x8,
        ItemClipsChildrenToShape = 0x10,
        ItemIgnoresTransformations = 0x20,
        ItemIgnoresParentOpacity = 0x40,
        ItemDoesntPropagateOpacityToChildren = 0x80,
        ItemStacksBehindParent = 0x100,
        ItemUsesExtendedStyleOption = 0x200,
        ItemHasNoContents = 0x400,
        ItemSendsGeometryChanges = 0x800,
        ItemAcceptsInputMethod = 0x1000,
        ItemNegativeZStacksBehindParent = 0x2000,
        ItemIsPanel = 0x4000,
        ItemIsFocusScope = 0x8000, // internal
        ItemSendsScenePositionChanges = 0x10000,
        ItemStopsClickFocusPropagation = 0x20000,
        ItemStopsFocusHandling = 0x40000,
        ItemContainsChildrenInShape = 0x80000
        // NB! Don't forget to increase the d_ptr->flags bit field by 1 when adding a new flag.
    };
    Q_DECLARE_FLAGS(GraphicsItemFlags, GraphicsItemFlag)

    enum GraphicsItemChange {
        ItemPositionChange,
        ItemMatrixChange,
        ItemVisibleChange,
        ItemEnabledChange,
        ItemSelectedChange,
        ItemParentChange,
        ItemChildAddedChange,
        ItemChildRemovedChange,
        ItemTransformChange,
        ItemPositionHasChanged,
        ItemTransformHasChanged,
        ItemSceneChange,
        ItemVisibleHasChanged,
        ItemEnabledHasChanged,
        ItemSelectedHasChanged,
        ItemParentHasChanged,
        ItemSceneHasChanged,
        ItemCursorChange,
        ItemCursorHasChanged,
        ItemToolTipChange,
        ItemToolTipHasChanged,
        ItemFlagsChange,
        ItemFlagsHaveChanged,
        ItemZValueChange,
        ItemZValueHasChanged,
        ItemOpacityChange,
        ItemOpacityHasChanged,
        ItemScenePositionHasChanged,
        ItemRotationChange,
        ItemRotationHasChanged,
        ItemScaleChange,
        ItemScaleHasChanged,
        ItemTransformOriginPointChange,
        ItemTransformOriginPointHasChanged
    };

    enum CacheMode {
        NoCache,
        ItemCoordinateCache,
        DeviceCoordinateCache
    };

    enum PanelModality
    {
        NonModal,
        PanelModal,
        SceneModal
    };

    explicit QGraphicsItem(QGraphicsItem *parent = Q_NULLPTR);
    virtual ~QGraphicsItem();

    QGraphicsScene *scene() const;

    QGraphicsItem *parentItem() const;
    QGraphicsItem *topLevelItem() const;
    QGraphicsObject *parentObject() const;
    QGraphicsWidget *parentWidget() const;
    QGraphicsWidget *topLevelWidget() const;
    QGraphicsWidget *window() const;
    QGraphicsItem *panel() const;
    void setParentItem(QGraphicsItem *parent);
#if QT_DEPRECATED_SINCE(5, 0)
    QT_DEPRECATED inline QList<QGraphicsItem *> children() const { return childItems(); }
#endif
    QList<QGraphicsItem *> childItems() const;
    bool isWidget() const;
    bool isWindow() const;
    bool isPanel() const;

    QGraphicsObject *toGraphicsObject();
    const QGraphicsObject *toGraphicsObject() const;

    QGraphicsItemGroup *group() const;
    void setGroup(QGraphicsItemGroup *group);

    GraphicsItemFlags flags() const;
    void setFlag(GraphicsItemFlag flag, bool enabled = true);
    void setFlags(GraphicsItemFlags flags);

    CacheMode cacheMode() const;
    void setCacheMode(CacheMode mode, const QSize &cacheSize = QSize());

    PanelModality panelModality() const;
    void setPanelModality(PanelModality panelModality);
    bool isBlockedByModalPanel(QGraphicsItem **blockingPanel = Q_NULLPTR) const;

#ifndef QT_NO_TOOLTIP
    QString toolTip() const;
    void setToolTip(const QString &toolTip);
#endif

#ifndef QT_NO_CURSOR
    QCursor cursor() const;
    void setCursor(const QCursor &cursor);
    bool hasCursor() const;
    void unsetCursor();
#endif

    bool isVisible() const;
    bool isVisibleTo(const QGraphicsItem *parent) const;
    void setVisible(bool visible);
    inline void hide() { setVisible(false); }
    inline void show() { setVisible(true); }

    bool isEnabled() const;
    void setEnabled(bool enabled);

    bool isSelected() const;
    void setSelected(bool selected);

    bool acceptDrops() const;
    void setAcceptDrops(bool on);

    qreal opacity() const;
    qreal effectiveOpacity() const;
    void setOpacity(qreal opacity);

#ifndef QT_NO_GRAPHICSEFFECT
    // Effect
    QGraphicsEffect *graphicsEffect() const;
    void setGraphicsEffect(QGraphicsEffect *effect);
#endif //QT_NO_GRAPHICSEFFECT

    Qt::MouseButtons acceptedMouseButtons() const;
    void setAcceptedMouseButtons(Qt::MouseButtons buttons);
#if QT_DEPRECATED_SINCE(5, 0)
    QT_DEPRECATED inline bool acceptsHoverEvents() const { return acceptHoverEvents(); }
    QT_DEPRECATED inline void setAcceptsHoverEvents(bool enabled) { setAcceptHoverEvents(enabled); }
#endif
    bool acceptHoverEvents() const;
    void setAcceptHoverEvents(bool enabled);
    bool acceptTouchEvents() const;
    void setAcceptTouchEvents(bool enabled);

    bool filtersChildEvents() const;
    void setFiltersChildEvents(bool enabled);

    bool handlesChildEvents() const;
    void setHandlesChildEvents(bool enabled);

    bool isActive() const;
    void setActive(bool active);

    bool hasFocus() const;
    void setFocus(Qt::FocusReason focusReason = Qt::OtherFocusReason);
    void clearFocus();

    QGraphicsItem *focusProxy() const;
    void setFocusProxy(QGraphicsItem *item);

    QGraphicsItem *focusItem() const;
    QGraphicsItem *focusScopeItem() const;

    void grabMouse();
    void ungrabMouse();
    void grabKeyboard();
    void ungrabKeyboard();

    // Positioning in scene coordinates
    QPointF pos() const;
    inline qreal x() const { return pos().x(); }
    void setX(qreal x);
    inline qreal y() const { return pos().y(); }
    void setY(qreal y);
    QPointF scenePos() const;
    void setPos(const QPointF &pos);
    inline void setPos(qreal x, qreal y);
    inline void moveBy(qreal dx, qreal dy) { setPos(pos().x() + dx, pos().y() + dy); }

    void ensureVisible(const QRectF &rect = QRectF(), int xmargin = 50, int ymargin = 50);
    inline void ensureVisible(qreal x, qreal y, qreal w, qreal h, int xmargin = 50, int ymargin = 50);

    // Local transformation
    QMatrix matrix() const;
    QMatrix sceneMatrix() const;
    void setMatrix(const QMatrix &matrix, bool combine = false);
    void resetMatrix();
    QTransform transform() const;
    QTransform sceneTransform() const;
    QTransform deviceTransform(const QTransform &viewportTransform) const;
    QTransform itemTransform(const QGraphicsItem *other, bool *ok = Q_NULLPTR) const;
    void setTransform(const QTransform &matrix, bool combine = false);
    void resetTransform();
#if QT_DEPRECATED_SINCE(5, 0)
    QT_DEPRECATED inline void rotate(qreal angle) { setTransform(QTransform().rotate(angle), true); }
    QT_DEPRECATED inline void scale(qreal sx, qreal sy) { setTransform(QTransform::fromScale(sx, sy), true); }
    QT_DEPRECATED inline void shear(qreal sh, qreal sv) { setTransform(QTransform().shear(sh, sv), true); }
    QT_DEPRECATED inline void translate(qreal dx, qreal dy) { setTransform(QTransform::fromTranslate(dx, dy), true); }
#endif
    void setRotation(qreal angle);
    qreal rotation() const;

    void setScale(qreal scale);
    qreal scale() const;

    QList<QGraphicsTransform *> transformations() const;
    void setTransformations(const QList<QGraphicsTransform *> &transformations);

    QPointF transformOriginPoint() const;
    void setTransformOriginPoint(const QPointF &origin);
    inline void setTransformOriginPoint(qreal ax, qreal ay)
    { setTransformOriginPoint(QPointF(ax,ay)); }

    virtual void advance(int phase);

    // Stacking order
    qreal zValue() const;
    void setZValue(qreal z);
    void stackBefore(const QGraphicsItem *sibling);

    // Hit test
    virtual QRectF boundingRect() const = 0;
    QRectF childrenBoundingRect() const;
    QRectF sceneBoundingRect() const;
    virtual QPainterPath shape() const;
    bool isClipped() const;
    QPainterPath clipPath() const;
    virtual bool contains(const QPointF &point) const;
    virtual bool collidesWithItem(const QGraphicsItem *other, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const;
    virtual bool collidesWithPath(const QPainterPath &path, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const;
    QList<QGraphicsItem *> collidingItems(Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const;
    bool isObscured(const QRectF &rect = QRectF()) const;
    inline bool isObscured(qreal x, qreal y, qreal w, qreal h) const;
    virtual bool isObscuredBy(const QGraphicsItem *item) const;
    virtual QPainterPath opaqueArea() const;

    QRegion boundingRegion(const QTransform &itemToDeviceTransform) const;
    qreal boundingRegionGranularity() const;
    void setBoundingRegionGranularity(qreal granularity);

    // Drawing
    virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = Q_NULLPTR) = 0;
    void update(const QRectF &rect = QRectF());
    inline void update(qreal x, qreal y, qreal width, qreal height);
    void scroll(qreal dx, qreal dy, const QRectF &rect = QRectF());

    // Coordinate mapping
    QPointF mapToItem(const QGraphicsItem *item, const QPointF &point) const;
    QPointF mapToParent(const QPointF &point) const;
    QPointF mapToScene(const QPointF &point) const;
    QPolygonF mapToItem(const QGraphicsItem *item, const QRectF &rect) const;
    QPolygonF mapToParent(const QRectF &rect) const;
    QPolygonF mapToScene(const QRectF &rect) const;
    QRectF mapRectToItem(const QGraphicsItem *item, const QRectF &rect) const;
    QRectF mapRectToParent(const QRectF &rect) const;
    QRectF mapRectToScene(const QRectF &rect) const;
    QPolygonF mapToItem(const QGraphicsItem *item, const QPolygonF &polygon) const;
    QPolygonF mapToParent(const QPolygonF &polygon) const;
    QPolygonF mapToScene(const QPolygonF &polygon) const;
    QPainterPath mapToItem(const QGraphicsItem *item, const QPainterPath &path) const;
    QPainterPath mapToParent(const QPainterPath &path) const;
    QPainterPath mapToScene(const QPainterPath &path) const;
    QPointF mapFromItem(const QGraphicsItem *item, const QPointF &point) const;
    QPointF mapFromParent(const QPointF &point) const;
    QPointF mapFromScene(const QPointF &point) const;
    QPolygonF mapFromItem(const QGraphicsItem *item, const QRectF &rect) const;
    QPolygonF mapFromParent(const QRectF &rect) const;
    QPolygonF mapFromScene(const QRectF &rect) const;
    QRectF mapRectFromItem(const QGraphicsItem *item, const QRectF &rect) const;
    QRectF mapRectFromParent(const QRectF &rect) const;
    QRectF mapRectFromScene(const QRectF &rect) const;
    QPolygonF mapFromItem(const QGraphicsItem *item, const QPolygonF &polygon) const;
    QPolygonF mapFromParent(const QPolygonF &polygon) const;
    QPolygonF mapFromScene(const QPolygonF &polygon) const;
    QPainterPath mapFromItem(const QGraphicsItem *item, const QPainterPath &path) const;
    QPainterPath mapFromParent(const QPainterPath &path) const;
    QPainterPath mapFromScene(const QPainterPath &path) const;

    inline QPointF mapToItem(const QGraphicsItem *item, qreal x, qreal y) const;
    inline QPointF mapToParent(qreal x, qreal y) const;
    inline QPointF mapToScene(qreal x, qreal y) const;
    inline QPolygonF mapToItem(const QGraphicsItem *item, qreal x, qreal y, qreal w, qreal h) const;
    inline QPolygonF mapToParent(qreal x, qreal y, qreal w, qreal h) const;
    inline QPolygonF mapToScene(qreal x, qreal y, qreal w, qreal h) const;
    inline QRectF mapRectToItem(const QGraphicsItem *item, qreal x, qreal y, qreal w, qreal h) const;
    inline QRectF mapRectToParent(qreal x, qreal y, qreal w, qreal h) const;
    inline QRectF mapRectToScene(qreal x, qreal y, qreal w, qreal h) const;
    inline QPointF mapFromItem(const QGraphicsItem *item, qreal x, qreal y) const;
    inline QPointF mapFromParent(qreal x, qreal y) const;
    inline QPointF mapFromScene(qreal x, qreal y) const;
    inline QPolygonF mapFromItem(const QGraphicsItem *item, qreal x, qreal y, qreal w, qreal h) const;
    inline QPolygonF mapFromParent(qreal x, qreal y, qreal w, qreal h) const;
    inline QPolygonF mapFromScene(qreal x, qreal y, qreal w, qreal h) const;
    inline QRectF mapRectFromItem(const QGraphicsItem *item, qreal x, qreal y, qreal w, qreal h) const;
    inline QRectF mapRectFromParent(qreal x, qreal y, qreal w, qreal h) const;
    inline QRectF mapRectFromScene(qreal x, qreal y, qreal w, qreal h) const;

    bool isAncestorOf(const QGraphicsItem *child) const;
    QGraphicsItem *commonAncestorItem(const QGraphicsItem *other) const;
    bool isUnderMouse() const;

    // Custom data
    QVariant data(int key) const;
    void setData(int key, const QVariant &value);

    Qt::InputMethodHints inputMethodHints() const;
    void setInputMethodHints(Qt::InputMethodHints hints);

    enum {
        Type = 1,
        UserType = 65536
    };
    virtual int type() const;

    void installSceneEventFilter(QGraphicsItem *filterItem);
    void removeSceneEventFilter(QGraphicsItem *filterItem);

protected:
    void updateMicroFocus();
    virtual bool sceneEventFilter(QGraphicsItem *watched, QEvent *event);
    virtual bool sceneEvent(QEvent *event);
    virtual void contextMenuEvent(QGraphicsSceneContextMenuEvent *event);
    virtual void dragEnterEvent(QGraphicsSceneDragDropEvent *event);
    virtual void dragLeaveEvent(QGraphicsSceneDragDropEvent *event);
    virtual void dragMoveEvent(QGraphicsSceneDragDropEvent *event);
    virtual void dropEvent(QGraphicsSceneDragDropEvent *event);
    virtual void focusInEvent(QFocusEvent *event);
    virtual void focusOutEvent(QFocusEvent *event);
    virtual void hoverEnterEvent(QGraphicsSceneHoverEvent *event);
    virtual void hoverMoveEvent(QGraphicsSceneHoverEvent *event);
    virtual void hoverLeaveEvent(QGraphicsSceneHoverEvent *event);
    virtual void keyPressEvent(QKeyEvent *event);
    virtual void keyReleaseEvent(QKeyEvent *event);
    virtual void mousePressEvent(QGraphicsSceneMouseEvent *event);
    virtual void mouseMoveEvent(QGraphicsSceneMouseEvent *event);
    virtual void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);
    virtual void mouseDoubleClickEvent(QGraphicsSceneMouseEvent *event);
    virtual void wheelEvent(QGraphicsSceneWheelEvent *event);
    virtual void inputMethodEvent(QInputMethodEvent *event);
    virtual QVariant inputMethodQuery(Qt::InputMethodQuery query) const;

    virtual QVariant itemChange(GraphicsItemChange change, const QVariant &value);

    enum Extension {
        UserExtension = 0x80000000
    };
    virtual bool supportsExtension(Extension extension) const;
    virtual void setExtension(Extension extension, const QVariant &variant);
    virtual QVariant extension(const QVariant &variant) const;

protected:
    QGraphicsItem(QGraphicsItemPrivate &dd, QGraphicsItem *parent);
    QScopedPointer<QGraphicsItemPrivate> d_ptr;

    void addToIndex();
    void removeFromIndex();
    void prepareGeometryChange();

private:
    Q_DISABLE_COPY(QGraphicsItem)
    Q_DECLARE_PRIVATE(QGraphicsItem)
    friend class QGraphicsItemGroup;
    friend class QGraphicsScene;
    friend class QGraphicsScenePrivate;
    friend class QGraphicsSceneFindItemBspTreeVisitor;
    friend class QGraphicsSceneBspTree;
    friend class QGraphicsView;
    friend class QGraphicsViewPrivate;
    friend class QGraphicsObject;
    friend class QGraphicsWidget;
    friend class QGraphicsWidgetPrivate;
    friend class QGraphicsProxyWidgetPrivate;
    friend class QGraphicsSceneIndex;
    friend class QGraphicsSceneIndexPrivate;
    friend class QGraphicsSceneBspTreeIndex;
    friend class QGraphicsSceneBspTreeIndexPrivate;
    friend class QGraphicsItemEffectSourcePrivate;
    friend class QGraphicsTransformPrivate;
#ifndef QT_NO_GESTURES
    friend class QGestureManager;
#endif
    friend class ::tst_QGraphicsItem;
    friend bool qt_closestLeaf(const QGraphicsItem *, const QGraphicsItem *);
    friend bool qt_closestItemFirst(const QGraphicsItem *, const QGraphicsItem *);
};

2.QGraphicsScene

class QGraphicsScene : public QObject

class Q_WIDGETS_EXPORT QGraphicsScene : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QBrush backgroundBrush READ backgroundBrush WRITE setBackgroundBrush)
    Q_PROPERTY(QBrush foregroundBrush READ foregroundBrush WRITE setForegroundBrush)
    Q_PROPERTY(ItemIndexMethod itemIndexMethod READ itemIndexMethod WRITE setItemIndexMethod)
    Q_PROPERTY(QRectF sceneRect READ sceneRect WRITE setSceneRect)
    Q_PROPERTY(int bspTreeDepth READ bspTreeDepth WRITE setBspTreeDepth)
    Q_PROPERTY(QPalette palette READ palette WRITE setPalette)
    Q_PROPERTY(QFont font READ font WRITE setFont)
    Q_PROPERTY(bool sortCacheEnabled READ isSortCacheEnabled WRITE setSortCacheEnabled)
    Q_PROPERTY(bool stickyFocus READ stickyFocus WRITE setStickyFocus)
    Q_PROPERTY(qreal minimumRenderSize READ minimumRenderSize WRITE setMinimumRenderSize)

public:
    enum ItemIndexMethod {
        BspTreeIndex,
        NoIndex = -1
    };

    enum SceneLayer {
        ItemLayer = 0x1,
        BackgroundLayer = 0x2,
        ForegroundLayer = 0x4,
        AllLayers = 0xffff
    };
    Q_DECLARE_FLAGS(SceneLayers, SceneLayer)

    QGraphicsScene(QObject *parent = Q_NULLPTR);
    QGraphicsScene(const QRectF &sceneRect, QObject *parent = Q_NULLPTR);
    QGraphicsScene(qreal x, qreal y, qreal width, qreal height, QObject *parent = Q_NULLPTR);
    virtual ~QGraphicsScene();

    QRectF sceneRect() const;
    inline qreal width() const { return sceneRect().width(); }
    inline qreal height() const { return sceneRect().height(); }
    void setSceneRect(const QRectF &rect);
    inline void setSceneRect(qreal x, qreal y, qreal w, qreal h)
    { setSceneRect(QRectF(x, y, w, h)); }

    void render(QPainter *painter,
                const QRectF &target = QRectF(), const QRectF &source = QRectF(),
                Qt::AspectRatioMode aspectRatioMode = Qt::KeepAspectRatio);

    ItemIndexMethod itemIndexMethod() const;
    void setItemIndexMethod(ItemIndexMethod method);

    bool isSortCacheEnabled() const;
    void setSortCacheEnabled(bool enabled);

    int bspTreeDepth() const;
    void setBspTreeDepth(int depth);

    QRectF itemsBoundingRect() const;

    QList<QGraphicsItem *> items(Qt::SortOrder order = Qt::DescendingOrder) const;

    QList<QGraphicsItem *> items(const QPointF &pos, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape, Qt::SortOrder order = Qt::DescendingOrder, const QTransform &deviceTransform = QTransform()) const;
    QList<QGraphicsItem *> items(const QRectF &rect, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape, Qt::SortOrder order = Qt::DescendingOrder, const QTransform &deviceTransform = QTransform()) const;
    QList<QGraphicsItem *> items(const QPolygonF &polygon, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape, Qt::SortOrder order = Qt::DescendingOrder, const QTransform &deviceTransform = QTransform()) const;
    QList<QGraphicsItem *> items(const QPainterPath &path, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape, Qt::SortOrder order = Qt::DescendingOrder, const QTransform &deviceTransform = QTransform()) const;

    QList<QGraphicsItem *> collidingItems(const QGraphicsItem *item, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const;
#if QT_DEPRECATED_SINCE(5, 0)
    QT_DEPRECATED inline QGraphicsItem *itemAt(const QPointF &position) const {
        QList<QGraphicsItem *> itemsAtPoint = items(position);
        return itemsAtPoint.isEmpty() ? Q_NULLPTR : itemsAtPoint.first();
    }
#endif
    QGraphicsItem *itemAt(const QPointF &pos, const QTransform &deviceTransform) const;
#if QT_DEPRECATED_SINCE(5, 0)
    QT_DEPRECATED inline QList<QGraphicsItem *> items(qreal x, qreal y, qreal w, qreal h, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const
    { return items(QRectF(x, y, w, h), mode); }
#endif
    inline QList<QGraphicsItem *> items(qreal x, qreal y, qreal w, qreal h, Qt::ItemSelectionMode mode, Qt::SortOrder order,
                                        const QTransform &deviceTransform = QTransform()) const
    { return items(QRectF(x, y, w, h), mode, order, deviceTransform); }
#if QT_DEPRECATED_SINCE(5, 0)
    QT_DEPRECATED inline QGraphicsItem *itemAt(qreal x, qreal y) const {
        QList<QGraphicsItem *> itemsAtPoint = items(QPointF(x, y));
        return itemsAtPoint.isEmpty() ? Q_NULLPTR : itemsAtPoint.first();
    }
#endif
    inline QGraphicsItem *itemAt(qreal x, qreal y, const QTransform &deviceTransform) const
    { return itemAt(QPointF(x, y), deviceTransform); }

    QList<QGraphicsItem *> selectedItems() const;
    QPainterPath selectionArea() const;
    void setSelectionArea(const QPainterPath &path, const QTransform &deviceTransform);
    void setSelectionArea(const QPainterPath &path, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape, const QTransform &deviceTransform = QTransform());
    void setSelectionArea(const QPainterPath &path, Qt::ItemSelectionOperation selectionOperation, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape, const QTransform &deviceTransform = QTransform());
    // ### Qt6 merge the last 2 functions and add a default: Qt::ItemSelectionOperation selectionOperation = Qt::ReplaceSelection

    QGraphicsItemGroup *createItemGroup(const QList<QGraphicsItem *> &items);
    void destroyItemGroup(QGraphicsItemGroup *group);

    void addItem(QGraphicsItem *item);
    QGraphicsEllipseItem *addEllipse(const QRectF &rect, const QPen &pen = QPen(), const QBrush &brush = QBrush());
    QGraphicsLineItem *addLine(const QLineF &line, const QPen &pen = QPen());
    QGraphicsPathItem *addPath(const QPainterPath &path, const QPen &pen = QPen(), const QBrush &brush = QBrush());
    QGraphicsPixmapItem *addPixmap(const QPixmap &pixmap);
    QGraphicsPolygonItem *addPolygon(const QPolygonF &polygon, const QPen &pen = QPen(), const QBrush &brush = QBrush());
    QGraphicsRectItem *addRect(const QRectF &rect, const QPen &pen = QPen(), const QBrush &brush = QBrush());
    QGraphicsTextItem *addText(const QString &text, const QFont &font = QFont());
    QGraphicsSimpleTextItem *addSimpleText(const QString &text, const QFont &font = QFont());
    QGraphicsProxyWidget *addWidget(QWidget *widget, Qt::WindowFlags wFlags = Qt::WindowFlags());
    inline QGraphicsEllipseItem *addEllipse(qreal x, qreal y, qreal w, qreal h, const QPen &pen = QPen(), const QBrush &brush = QBrush())
    { return addEllipse(QRectF(x, y, w, h), pen, brush); }
    inline QGraphicsLineItem *addLine(qreal x1, qreal y1, qreal x2, qreal y2, const QPen &pen = QPen())
    { return addLine(QLineF(x1, y1, x2, y2), pen); }
    inline QGraphicsRectItem *addRect(qreal x, qreal y, qreal w, qreal h, const QPen &pen = QPen(), const QBrush &brush = QBrush())
    { return addRect(QRectF(x, y, w, h), pen, brush); }
    void removeItem(QGraphicsItem *item);

    QGraphicsItem *focusItem() const;
    void setFocusItem(QGraphicsItem *item, Qt::FocusReason focusReason = Qt::OtherFocusReason);
    bool hasFocus() const;
    void setFocus(Qt::FocusReason focusReason = Qt::OtherFocusReason);
    void clearFocus();

    void setStickyFocus(bool enabled);
    bool stickyFocus() const;

    QGraphicsItem *mouseGrabberItem() const;

    QBrush backgroundBrush() const;
    void setBackgroundBrush(const QBrush &brush);

    QBrush foregroundBrush() const;
    void setForegroundBrush(const QBrush &brush);

    virtual QVariant inputMethodQuery(Qt::InputMethodQuery query) const;

    QList <QGraphicsView *> views() const;

    inline void update(qreal x, qreal y, qreal w, qreal h)
    { update(QRectF(x, y, w, h)); }
    inline void invalidate(qreal x, qreal y, qreal w, qreal h, SceneLayers layers = AllLayers)
    { invalidate(QRectF(x, y, w, h), layers); }

    QStyle *style() const;
    void setStyle(QStyle *style);

    QFont font() const;
    void setFont(const QFont &font);

    QPalette palette() const;
    void setPalette(const QPalette &palette);

    bool isActive() const;
    QGraphicsItem *activePanel() const;
    void setActivePanel(QGraphicsItem *item);
    QGraphicsWidget *activeWindow() const;
    void setActiveWindow(QGraphicsWidget *widget);

    bool sendEvent(QGraphicsItem *item, QEvent *event);

    qreal minimumRenderSize() const;
    void setMinimumRenderSize(qreal minSize);

public Q_SLOTS:
    void update(const QRectF &rect = QRectF());
    void invalidate(const QRectF &rect = QRectF(), SceneLayers layers = AllLayers);
    void advance();
    void clearSelection();
    void clear();

protected:
    bool event(QEvent *event) Q_DECL_OVERRIDE;
    bool eventFilter(QObject *watched, QEvent *event) Q_DECL_OVERRIDE;
    virtual void contextMenuEvent(QGraphicsSceneContextMenuEvent *event);
    virtual void dragEnterEvent(QGraphicsSceneDragDropEvent *event);
    virtual void dragMoveEvent(QGraphicsSceneDragDropEvent *event);
    virtual void dragLeaveEvent(QGraphicsSceneDragDropEvent *event);
    virtual void dropEvent(QGraphicsSceneDragDropEvent *event);
    virtual void focusInEvent(QFocusEvent *event);
    virtual void focusOutEvent(QFocusEvent *event);
    virtual void helpEvent(QGraphicsSceneHelpEvent *event);
    virtual void keyPressEvent(QKeyEvent *event);
    virtual void keyReleaseEvent(QKeyEvent *event);
    virtual void mousePressEvent(QGraphicsSceneMouseEvent *event);
    virtual void mouseMoveEvent(QGraphicsSceneMouseEvent *event);
    virtual void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);
    virtual void mouseDoubleClickEvent(QGraphicsSceneMouseEvent *event);
    virtual void wheelEvent(QGraphicsSceneWheelEvent *event);
    virtual void inputMethodEvent(QInputMethodEvent *event);

    virtual void drawBackground(QPainter *painter, const QRectF &rect);
    virtual void drawForeground(QPainter *painter, const QRectF &rect);
    virtual void drawItems(QPainter *painter, int numItems,
                           QGraphicsItem *items[],
                           const QStyleOptionGraphicsItem options[],
                           QWidget *widget = Q_NULLPTR);

protected Q_SLOTS:
    // ### Qt 6: make unconditional
#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
    virtual
#endif
    bool focusNextPrevChild(bool next);

Q_SIGNALS:
    void changed(const QList<QRectF> &region);
    void sceneRectChanged(const QRectF &rect);
    void selectionChanged();
    void focusItemChanged(QGraphicsItem *newFocus, QGraphicsItem *oldFocus, Qt::FocusReason reason);

private:
    Q_DECLARE_PRIVATE(QGraphicsScene)
    Q_DISABLE_COPY(QGraphicsScene)
    Q_PRIVATE_SLOT(d_func(), void _q_emitUpdated())
    Q_PRIVATE_SLOT(d_func(), void _q_polishItems())
    Q_PRIVATE_SLOT(d_func(), void _q_processDirtyItems())
    Q_PRIVATE_SLOT(d_func(), void _q_updateScenePosDescendants())
    friend class QGraphicsItem;
    friend class QGraphicsItemPrivate;
    friend class QGraphicsObject;
    friend class QGraphicsView;
    friend class QGraphicsViewPrivate;
    friend class QGraphicsWidget;
    friend class QGraphicsWidgetPrivate;
    friend class QGraphicsEffect;
    friend class QGraphicsSceneIndex;
    friend class QGraphicsSceneIndexPrivate;
    friend class QGraphicsSceneBspTreeIndex;
    friend class QGraphicsSceneBspTreeIndexPrivate;
    friend class QGraphicsItemEffectSourcePrivate;
#ifndef QT_NO_GESTURES
    friend class QGesture;
#endif
};

3.QGraphicsView 

class QGraphicsView : public QAbstractScrollArea
class QAbstractScrollArea : public QFrame
class QFrame : public QWidget
class QWidget : public QObject, public QPaintDevice

class Q_WIDGETS_EXPORT QGraphicsView : public QAbstractScrollArea
{
    Q_OBJECT
    Q_FLAGS(QPainter::RenderHints CacheMode OptimizationFlags)
    Q_PROPERTY(QBrush backgroundBrush READ backgroundBrush WRITE setBackgroundBrush)
    Q_PROPERTY(QBrush foregroundBrush READ foregroundBrush WRITE setForegroundBrush)
    Q_PROPERTY(bool interactive READ isInteractive WRITE setInteractive)
    Q_PROPERTY(QRectF sceneRect READ sceneRect WRITE setSceneRect)
    Q_PROPERTY(Qt::Alignment alignment READ alignment WRITE setAlignment)
    Q_PROPERTY(QPainter::RenderHints renderHints READ renderHints WRITE setRenderHints)
    Q_PROPERTY(DragMode dragMode READ dragMode WRITE setDragMode)
    Q_PROPERTY(CacheMode cacheMode READ cacheMode WRITE setCacheMode)
    Q_PROPERTY(ViewportAnchor transformationAnchor READ transformationAnchor WRITE setTransformationAnchor)
    Q_PROPERTY(ViewportAnchor resizeAnchor READ resizeAnchor WRITE setResizeAnchor)
    Q_PROPERTY(ViewportUpdateMode viewportUpdateMode READ viewportUpdateMode WRITE setViewportUpdateMode)
#ifndef QT_NO_RUBBERBAND
    Q_PROPERTY(Qt::ItemSelectionMode rubberBandSelectionMode READ rubberBandSelectionMode WRITE setRubberBandSelectionMode)
#endif
    Q_PROPERTY(OptimizationFlags optimizationFlags READ optimizationFlags WRITE setOptimizationFlags)

public:
    enum ViewportAnchor {
        NoAnchor,
        AnchorViewCenter,
        AnchorUnderMouse
    };
    Q_ENUM(ViewportAnchor)

    enum CacheModeFlag {
        CacheNone = 0x0,
        CacheBackground = 0x1
    };
    Q_DECLARE_FLAGS(CacheMode, CacheModeFlag)

    enum DragMode {
        NoDrag,
        ScrollHandDrag,
        RubberBandDrag
    };
    Q_ENUM(DragMode)

    enum ViewportUpdateMode {
        FullViewportUpdate,
        MinimalViewportUpdate,
        SmartViewportUpdate,
        NoViewportUpdate,
        BoundingRectViewportUpdate
    };
    Q_ENUM(ViewportUpdateMode)

    enum OptimizationFlag {
        DontClipPainter = 0x1, // obsolete
        DontSavePainterState = 0x2,
        DontAdjustForAntialiasing = 0x4,
        IndirectPainting = 0x8
    };
    Q_DECLARE_FLAGS(OptimizationFlags, OptimizationFlag)

    QGraphicsView(QWidget *parent = Q_NULLPTR);
    QGraphicsView(QGraphicsScene *scene, QWidget *parent = Q_NULLPTR);
    ~QGraphicsView();

    QSize sizeHint() const Q_DECL_OVERRIDE;

    QPainter::RenderHints renderHints() const;
    void setRenderHint(QPainter::RenderHint hint, bool enabled = true);
    void setRenderHints(QPainter::RenderHints hints);

    Qt::Alignment alignment() const;
    void setAlignment(Qt::Alignment alignment);

    ViewportAnchor transformationAnchor() const;
    void setTransformationAnchor(ViewportAnchor anchor);

    ViewportAnchor resizeAnchor() const;
    void setResizeAnchor(ViewportAnchor anchor);

    ViewportUpdateMode viewportUpdateMode() const;
    void setViewportUpdateMode(ViewportUpdateMode mode);

    OptimizationFlags optimizationFlags() const;
    void setOptimizationFlag(OptimizationFlag flag, bool enabled = true);
    void setOptimizationFlags(OptimizationFlags flags);

    DragMode dragMode() const;
    void setDragMode(DragMode mode);

#ifndef QT_NO_RUBBERBAND
    Qt::ItemSelectionMode rubberBandSelectionMode() const;
    void setRubberBandSelectionMode(Qt::ItemSelectionMode mode);
    QRect rubberBandRect() const;
#endif

    CacheMode cacheMode() const;
    void setCacheMode(CacheMode mode);
    void resetCachedContent();

    bool isInteractive() const;
    void setInteractive(bool allowed);

    QGraphicsScene *scene() const;
    void setScene(QGraphicsScene *scene);

    QRectF sceneRect() const;
    void setSceneRect(const QRectF &rect);
    inline void setSceneRect(qreal x, qreal y, qreal w, qreal h);

    QMatrix matrix() const;
    void setMatrix(const QMatrix &matrix, bool combine = false);
    void resetMatrix();
    QTransform transform() const;
    QTransform viewportTransform() const;
    bool isTransformed() const;
    void setTransform(const QTransform &matrix, bool combine = false);
    void resetTransform();
    void rotate(qreal angle);
    void scale(qreal sx, qreal sy);
    void shear(qreal sh, qreal sv);
    void translate(qreal dx, qreal dy);

    void centerOn(const QPointF &pos);
    inline void centerOn(qreal x, qreal y);
    void centerOn(const QGraphicsItem *item);
    void ensureVisible(const QRectF &rect, int xmargin = 50, int ymargin = 50);
    inline void ensureVisible(qreal x, qreal y, qreal w, qreal h, int xmargin = 50, int ymargin = 50);
    void ensureVisible(const QGraphicsItem *item, int xmargin = 50, int ymargin = 50);
    void fitInView(const QRectF &rect, Qt::AspectRatioMode aspectRadioMode = Qt::IgnoreAspectRatio);
    inline void fitInView(qreal x, qreal y, qreal w, qreal h,
                          Qt::AspectRatioMode aspectRadioMode = Qt::IgnoreAspectRatio);
    void fitInView(const QGraphicsItem *item,
                   Qt::AspectRatioMode aspectRadioMode = Qt::IgnoreAspectRatio);

    void render(QPainter *painter, const QRectF &target = QRectF(), const QRect &source = QRect(),
                Qt::AspectRatioMode aspectRatioMode = Qt::KeepAspectRatio);

    QList<QGraphicsItem *> items() const;
    QList<QGraphicsItem *> items(const QPoint &pos) const;
    inline QList<QGraphicsItem *> items(int x, int y) const;
    QList<QGraphicsItem *> items(const QRect &rect, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const;
    inline QList<QGraphicsItem *> items(int x, int y, int w, int h, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const;
    QList<QGraphicsItem *> items(const QPolygon &polygon, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const;
    QList<QGraphicsItem *> items(const QPainterPath &path, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const;
    QGraphicsItem *itemAt(const QPoint &pos) const;
    inline QGraphicsItem *itemAt(int x, int y) const;

    QPointF mapToScene(const QPoint &point) const;
    QPolygonF mapToScene(const QRect &rect) const;
    QPolygonF mapToScene(const QPolygon &polygon) const;
    QPainterPath mapToScene(const QPainterPath &path) const;
    QPoint mapFromScene(const QPointF &point) const;
    QPolygon mapFromScene(const QRectF &rect) const;
    QPolygon mapFromScene(const QPolygonF &polygon) const;
    QPainterPath mapFromScene(const QPainterPath &path) const;
    inline QPointF mapToScene(int x, int y) const;
    inline QPolygonF mapToScene(int x, int y, int w, int h) const;
    inline QPoint mapFromScene(qreal x, qreal y) const;
    inline QPolygon mapFromScene(qreal x, qreal y, qreal w, qreal h) const;

    QVariant inputMethodQuery(Qt::InputMethodQuery query) const Q_DECL_OVERRIDE;

    QBrush backgroundBrush() const;
    void setBackgroundBrush(const QBrush &brush);

    QBrush foregroundBrush() const;
    void setForegroundBrush(const QBrush &brush);

public Q_SLOTS:
    void updateScene(const QList<QRectF> &rects);
    void invalidateScene(const QRectF &rect = QRectF(), QGraphicsScene::SceneLayers layers = QGraphicsScene::AllLayers);
    void updateSceneRect(const QRectF &rect);

#ifndef QT_NO_RUBBERBAND
Q_SIGNALS:
    void rubberBandChanged(QRect viewportRect, QPointF fromScenePoint, QPointF toScenePoint);
#endif

protected Q_SLOTS:
    void setupViewport(QWidget *widget) Q_DECL_OVERRIDE;

protected:
    QGraphicsView(QGraphicsViewPrivate &, QWidget *parent = Q_NULLPTR);
    bool event(QEvent *event) Q_DECL_OVERRIDE;
    bool viewportEvent(QEvent *event) Q_DECL_OVERRIDE;

#ifndef QT_NO_CONTEXTMENU
    void contextMenuEvent(QContextMenuEvent *event) Q_DECL_OVERRIDE;
#endif
#if QT_CONFIG(draganddrop)
    void dragEnterEvent(QDragEnterEvent *event) Q_DECL_OVERRIDE;
    void dragLeaveEvent(QDragLeaveEvent *event) Q_DECL_OVERRIDE;
    void dragMoveEvent(QDragMoveEvent *event) Q_DECL_OVERRIDE;
    void dropEvent(QDropEvent *event) Q_DECL_OVERRIDE;
#endif
    void focusInEvent(QFocusEvent *event) Q_DECL_OVERRIDE;
    bool focusNextPrevChild(bool next) Q_DECL_OVERRIDE;
    void focusOutEvent(QFocusEvent *event) Q_DECL_OVERRIDE;
    void keyPressEvent(QKeyEvent *event) Q_DECL_OVERRIDE;
    void keyReleaseEvent(QKeyEvent *event) Q_DECL_OVERRIDE;
    void mouseDoubleClickEvent(QMouseEvent *event) Q_DECL_OVERRIDE;
    void mousePressEvent(QMouseEvent *event) Q_DECL_OVERRIDE;
    void mouseMoveEvent(QMouseEvent *event) Q_DECL_OVERRIDE;
    void mouseReleaseEvent(QMouseEvent *event) Q_DECL_OVERRIDE;
#ifndef QT_NO_WHEELEVENT
    void wheelEvent(QWheelEvent *event) Q_DECL_OVERRIDE;
#endif
    void paintEvent(QPaintEvent *event) Q_DECL_OVERRIDE;
    void resizeEvent(QResizeEvent *event) Q_DECL_OVERRIDE;
    void scrollContentsBy(int dx, int dy) Q_DECL_OVERRIDE;
    void showEvent(QShowEvent *event) Q_DECL_OVERRIDE;
    void inputMethodEvent(QInputMethodEvent *event) Q_DECL_OVERRIDE;

    virtual void drawBackground(QPainter *painter, const QRectF &rect);
    virtual void drawForeground(QPainter *painter, const QRectF &rect);
    virtual void drawItems(QPainter *painter, int numItems,
                           QGraphicsItem *items[],
                           const QStyleOptionGraphicsItem options[]);

private:
    Q_DECLARE_PRIVATE(QGraphicsView)
    Q_DISABLE_COPY(QGraphicsView)
#ifndef QT_NO_CURSOR
    Q_PRIVATE_SLOT(d_func(), void _q_setViewportCursor(const QCursor &))
    Q_PRIVATE_SLOT(d_func(), void _q_unsetViewportCursor())
#endif
    friend class QGraphicsSceneWidget;
    friend class QGraphicsScene;
    friend class QGraphicsScenePrivate;
    friend class QGraphicsItemPrivate;
};