qgraphicsview.cpp

奇趣公司比较新的qt/emd版本

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//#define QGRAPHICSVIEW_DEBUG

static const int QGRAPHICSVIEW_REGION_RECT_THRESHOLD = 50;

/*!
    \class QGraphicsView
    \brief The QGraphicsView class provides a widget for displaying the
    contents of a QGraphicsScene.
    \since 4.2
    \ingroup multimedia
    \mainclass

    QGraphicsView visualizes the contents of a QGraphicsScene in a scrollable
    viewport. To create a scene with geometrical items, see QGraphicsScene's
    documentation. QGraphicsView is part of \l{The Graphics View Framework}.

    To visualize a scene, you start by constructing a QGraphicsView object,
    passing the address of the scene you want to visualize to QGraphicsView's
    constructor. Alternatively, you can call setScene() to set the scene at a
    later point. After you call show(), the view will by default scroll to the
    center of the scene and display any items that are visible at this
    point. For example:

    \code
        QGraphicsScene scene;
        scene.addText("Hello, world!");

        QGraphicsView view(&scene);
        view.show();
    \endcode

    You can explicitly scroll to any position on the scene by using the
    scroll bars, or by calling centerOn(). By passing a point to centerOn(),
    QGraphicsView will scroll its viewport to ensure that the point is
    centered in the view. An overload is provided for scrolling to a
    QGraphicsItem, in which case QGraphicsView will see to that the center of
    the item is centered in the view. If all you want is to ensure that a
    certain area is visible, (but not necessarily centered,) you can call
    ensureVisible() instead.

    QGraphicsView can be used to visualize a whole scene, or only parts of it.
    The visualized area is by default detected automatically when the view is
    displayed for the first time (by calling
    QGraphicsScene::itemsBoundingRect()). To set the visualized area rectangle
    yourself, you can call setSceneRect(). This will adjust the scroll bars'
    ranges appropriately. Note that although the scene supports a virtually
    unlimited size, the range of the scroll bars will never exceed the range of
    an integer (INT_MIN, INT_MAX). When the scene is larger than the scroll
    bars' values, you can choose to use translate() to navigate the scene
    instead.

    QGraphicsView visualizes the scene by calling render(). By default, the
    items are drawn onto the viewport by using a regular QPainter, and using
    default render hints. To change the default render hints that
    QGraphicsView passes to QPainter when painting items, you can call
    setRenderHints().

    By default, QGraphicsView provides a regular QWidget for the viewport
    widget. You can access this widget by calling viewport(), or you can
    replace it by calling setViewport(). To render using OpenGL, simply call
    setViewport(new QGLWidget). QGraphicsView takes ownership of the viewport
    widget.

    QGraphicsView supports affine transformations, using QMatrix. You can
    either pass a matrix to setMatrix(), or you can call one of the
    convenience functions rotate(), scale(), translate() or shear(). The most
    two common transformations are scaling, which is used to implement
    zooming, and rotation. QGraphicsView keeps the center of the view fixed
    during a transformation.

    You can interact with the items on the scene by using the mouse and
    keyboard. QGraphicsView translates the mouse and key events into \e scene
    events, (events that inherit QGraphicsSceneEvent,), and forward them to
    the visualized scene. In the end, it's the individual item that handles
    the events and reacts to them. For example, if you click on a selectable
    item, the item will typically let the scene know that it has been
    selected, and it will also redraw itself to display a selection
    rectangle. Similiary, if you click and drag the mouse to move a movable
    item, it's the item that handles the mouse moves and moves itself.  Item
    interaction is enabled by default, and you can toggle it by calling
    setInteractive().

    You can also provide your own custom scene interaction, by creating a
    subclass of QGraphicsView, and reimplementing the mouse and key event
    handlers. To simplify how you programmatically interact with items in the
    view, QGraphicsView provides the mapping functions mapToScene() and
    mapFromScene(), and the item accessors items() and itemAt(). These
    functions allow you to map points, rectangles, polygons and paths between
    view coordinates and scene coordinates, and to find items on the scene
    using view coordinates.

    \img graphicsview-view.png

    \sa QGraphicsScene, QGraphicsItem, QGraphicsSceneEvent
*/

/*!
    \enum QGraphicsView::ViewportAnchor

    This enums describe the possible anchors that QGraphicsView can
    use when the user resizes the view or when the view is
    transformed.

    \value NoAnchor No anchor, i.e. the view leaves the scene's
                    position unchanged.
    \value AnchorViewCenter The scene point at the center of the view
                            is used as the anchor.
    \value AnchorUnderMouse The point under the mouse is used as the anchor.

    \sa resizeAnchor, transformationAnchor
*/

/*!
    \enum QGraphicsView::ViewportUpdateMode

    \since 4.3

    This enum describes how QGraphicsView updates its viewport when the scene
    contents change or are exposed.

    \value FullViewportUpdate When any visible part of the scene changes or is
    reexposed, QGraphicsView will update the entire viewport. This approach is
    fastest when QGraphicsView spends more time figuring out what to draw than
    it would spend drawing (e.g., when very many small items are repeatedly
    updated). This is the preferred update mode for viewports that do not
    support partial updates, such as QGLWidget.

    \value MinimalViewportUpdate QGraphicsView will determine the minimal
    viewport region that requires a redraw, minimizing the time spent drawing
    by avoiding a redraw of areas that have not changed. This is
    QGraphicsView's default mode. Although this approach provides the best
    performance in general, if there are many small visible changes on the
    scene, QGraphicsView might end up spending more time finding the minimal
    approach than it will spend drawing.

    \value SmartViewportUpdate QGraphicsView will attempt to find an optimal
    update mode by analyzing the areas that require a redraw.

    \value NoViewportUpdate QGraphicsView will never update its viewport when
    the scene changes; the user is expected to control all updates. This mode
    disables all (potentially slow) item visibility testing in QGraphicsView,
    and is suitable for scenes that either require a fixed frame rate, or where
    the viewport is otherwise updated externally.

    \sa viewportUpdateMode
*/

/*!
    \enum QGraphicsView::OptimizationFlag

    \since 4.3

    This enum describes flags that you can enable to improve rendering
    performance in QGraphicsView. By default, none of these flags are set.
    Note that setting a flag usually imposes a side effect, and this effect
    can vary between paint devices and platforms.

    \value DontClipPainter QGraphicsView sometimes clips the painter when
    rendering the scene contents. This can generally improve performance
    (e.g., rendering only small parts of a large pixmap), and protects against
    rendering mistakes (e.g., drawing outside bounding rectangles, or outside
    the exposed area). In some situations, however, the painter clip can slow
    down rendering; especially when all painting is restricted to inside
    exposed areas. By enabling this flag, QGraphicsView will completely
    disable its implicit clipping. Note that rendering artifacts from using a
    semi-transparent foreground or background brush can occur if clipping is
    disabled.

    \value DontSavePainterState When rendering, QGraphicsView protects the
    painter state (see QPainter::save()) when rendering the background or
    foreground, and when rendering each item. This allows you to leave the
    painter in an altered state (i.e., you can call QPainter::setPen() or
    QPainter::setBrush() without restoring the state after painting). However,
    if the items consistently do restore the state, you should enable this
    flag to prevent QGraphicsView from doing the same.

    \value DontAdjustForAntialiasing Disables QGraphicsView's antialiasing
    auto-adjustment of exposed areas. Items that render antialiased lines on
    the boundaries of their QGraphicsItem::boundingRect() can end up rendering
    parts of the line outside. To prevent rendering artifacts, QGraphicsView
    expands all exposed regions by 2 pixels in all directions. If you enable
    this flag, QGraphicsView will no longer perform these adjustments,
    minimizing the areas that require redrawing, which improves performance. A
    common side effect is that items that do draw with antialiasing can leave
    painting traces behind on the scene as they are moved.
*/

/*!
    \enum QGraphicsView::CacheModeFlag

    This enum describes the flags that you can set for a QGraphicsView's cache
    mode.

    \value CacheNone All painting is done directly onto the viewport.

    \value CacheBackground The background is cached. This affects both custom
    backgrounds, and backgrounds based on the backgroundBrush property. When
    this flag is enabled, QGraphicsView will allocate one pixmap with the full
    size of the viewport.

    \sa cacheMode
*/

/*!
    \enum QGraphicsView::DragMode

    This enum describes the default action for the view when pressing and
    dragging the mouse over the viewport.

    \value NoDrag Nothing happens; the mouse event is ignored.

    \value ScrollHandDrag The cursor changes into a pointing hand, and
    dragging the mouse around will scroll the scrolbars. This mode works both
    in \l{QGraphicsView::interactive}{interactive} and non-interactive mode.

    \value RubberBandDrag A rubber band will appear. Dragging the mouse will
    set the rubber band geometry, and all items covered by the rubber band are
    selected. This mode is disabled for non-interactive views.

    \sa dragMode, QGraphicsScene::setSelectionArea()
*/

#include "qgraphicsview.h"

#ifndef QT_NO_GRAPHICSVIEW

#include "qgraphicsitem.h"
#include "qgraphicsitem_p.h"
#include "qgraphicsscene.h"
#include "qgraphicsscene_p.h"
#include "qgraphicssceneevent.h"

#include <QtCore/qdatetime.h>
#include <QtCore/qdebug.h>
#include <QtGui/qapplication.h>
#include <QtGui/qdesktopwidget.h>
#include <QtGui/qevent.h>
#include <QtGui/qlayout.h>
#include <QtGui/qtransform.h>
#include <QtGui/qmatrix.h>
#include <QtGui/qpainter.h>
#include <QtGui/qscrollbar.h>
#include <QtGui/qstyleoption.h>
#include <private/qabstractscrollarea_p.h>

#include <math.h>

class QGraphicsViewPrivate : public QAbstractScrollAreaPrivate
{
    Q_DECLARE_PUBLIC(QGraphicsView)
public:
    QGraphicsViewPrivate();

    void recalculateContentSize();
    void centerView(QGraphicsView::ViewportAnchor anchor);

    QPainter::RenderHints renderHints;

    QGraphicsView::DragMode dragMode;
    bool sceneInteractionAllowed;
    QRectF sceneRect;
    bool hasSceneRect;
    void updateLastCenterPoint();

    qint64 horizontalScroll() const;
    qint64 verticalScroll() const;

    QList<QGraphicsItem *> itemsInArea(const QPainterPath &path,
                                       Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const;

    QPointF mousePressItemPoint;
    QPointF mousePressScenePoint;
    QPoint mousePressViewPoint;
    QPoint mousePressScreenPoint;
    QPointF lastMouseMoveScenePoint;
    QPoint lastMouseMoveScreenPoint;
    Qt::MouseButton mousePressButton;
    QTransform matrix;
    bool accelerateScrolling;
    qreal leftIndent;
    qreal topIndent;

    // Replaying events
    QGraphicsItem *lastItemUnderCursor;
    QPointF lastItemUnderCursorPos;

    // Replaying mouse events
    QMouseEvent lastMouseEvent;
    bool useLastMouseEvent;
    void replayLastMouseEvent();
    void storeMouseEvent(QMouseEvent *event);

    QPointF lastCenterPoint;
    bool keepLastCenterPoint;
    Qt::Alignment alignment;

    QGraphicsView::ViewportAnchor transformationAnchor;
    QGraphicsView::ViewportAnchor resizeAnchor;
    QGraphicsView::ViewportUpdateMode viewportUpdateMode;
    QGraphicsView::OptimizationFlags optimizationFlags;

    QPointer<QGraphicsScene> scene;
#ifndef QT_NO_RUBBERBAND
    QRect rubberBandRect;
    QRegion rubberBandRegion(const QWidget *widget, const QRect &rect) const;
    bool rubberBanding;
    Qt::ItemSelectionMode rubberBandSelectionMode;
#endif
    bool handScrolling;
    int handScrollMotions;

    QGraphicsView::CacheMode cacheMode;

    QBrush backgroundBrush;
    QBrush foregroundBrush;
    QPixmap backgroundPixmap;
    bool mustResizeBackgroundPixmap;
    QRegion backgroundPixmapExposed;

#ifndef QT_NO_CURSOR
    QCursor originalCursor;
    bool hasStoredOriginalCursor;
    void _q_setViewportCursor(const QCursor &cursor);
    void _q_unsetViewportCursor();
#endif

    QGraphicsSceneDragDropEvent *lastDragDropEvent;
    void storeDragDropEvent(const QGraphicsSceneDragDropEvent *event);
    void populateSceneDragDropEvent(QGraphicsSceneDragDropEvent *dest,
                                    QDropEvent *source);
};

/*!
    \internal
*/
QGraphicsViewPrivate::QGraphicsViewPrivate()
    : renderHints(QPainter::TextAntialiasing),
      dragMode(QGraphicsView::NoDrag),
      sceneInteractionAllowed(true), hasSceneRect(false), accelerateScrolling(true),
      leftIndent(0), topIndent(0), lastItemUnderCursor(0),
      lastMouseEvent(QEvent::None, QPoint(), Qt::NoButton, 0, 0),
      useLastMouseEvent(false),
      keepLastCenterPoint(true),
      alignment(Qt::AlignCenter),
      transformationAnchor(QGraphicsView::AnchorViewCenter), resizeAnchor(QGraphicsView::NoAnchor),
      viewportUpdateMode(QGraphicsView::MinimalViewportUpdate),
      optimizationFlags(0),
      scene(0),
#ifndef QT_NO_RUBBERBAND