qt-everywhere-src-5.15.1/qtbase/src/widgets/doc/snippets/code/src_gui_graphicsview_qgraphicsitem.cpp

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//! [0]
class SimpleItem : public QGraphicsItem
{
public:
    QRectF boundingRect() const override
    {
        qreal penWidth = 1;
        return QRectF(-10 - penWidth / 2, -10 - penWidth / 2,
                      20 + penWidth, 20 + penWidth);
    }

    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
               QWidget *widget) override
    {
        painter->drawRoundedRect(-10, -10, 20, 20, 5, 5);
    }
};
//! [0]


//! [1]
class CustomItem : public QGraphicsItem
{
public:
   enum { Type = UserType + 1 };

   int type() const override
   {
       // Enable the use of qgraphicsitem_cast with this item.
       return Type;
   }
   ...
};
//! [1]


//! [2]
item->setCursor(Qt::IBeamCursor);
//! [2]


//! [3]
item->setCursor(Qt::IBeamCursor);
//! [3]


//! [4]
QGraphicsRectItem rect;
rect.setPos(100, 100);

rect.sceneTransform().map(QPointF(0, 0));
// returns QPointF(100, 100);

rect.sceneTransform().inverted().map(QPointF(100, 100));
// returns QPointF(0, 0);
//! [4]


//! [5]
QGraphicsRectItem rect;
rect.setPos(100, 100);

rect.deviceTransform(view->viewportTransform()).map(QPointF(0, 0));
// returns the item's (0, 0) point in view's viewport coordinates

rect.deviceTransform(view->viewportTransform()).inverted().map(QPointF(100, 100));
// returns view's viewport's (100, 100) coordinate in item coordinates
//! [5]


//! [6]
// Rotate an item 45 degrees around (0, 0).
item->rotate(45);

// Rotate an item 45 degrees around (x, y).
item->setTransform(QTransform().translate(x, y).rotate(45).translate(-x, -y));
//! [6]


//! [7]
// Scale an item by 3x2 from its origin
item->scale(3, 2);

// Scale an item by 3x2 from (x, y)
item->setTransform(QTransform().translate(x, y).scale(3, 2).translate(-x, -y));
//! [7]


//! [8]
QRectF CircleItem::boundingRect() const
{
    qreal penWidth = 1;
    return QRectF(-radius - penWidth / 2, -radius - penWidth / 2,
                  diameter + penWidth, diameter + penWidth);
}
//! [8]


//! [9]
QPainterPath RoundItem::shape() const
{
    QPainterPath path;
    path.addEllipse(boundingRect());
    return path;
}
//! [9]


//! [10]
void RoundRectItem::paint(QPainter *painter,
                          const QStyleOptionGraphicsItem *option,
                          QWidget *widget)
{
    painter->drawRoundedRect(-10, -10, 20, 20, 5, 5);
}
//! [10]


//! [11]
static const int ObjectName = 0;

QGraphicsItem *item = scene.itemAt(100, 50);
if (item->data(ObjectName).toString().isEmpty()) {
    if (qgraphicsitem_cast<ButtonItem *>(item))
        item->setData(ObjectName, "Button");
}
//! [11]


//! [12]
QGraphicsScene scene;
QGraphicsEllipseItem *ellipse = scene.addEllipse(QRectF(-10, -10, 20, 20));
QGraphicsLineItem *line = scene.addLine(QLineF(-10, -10, 20, 20));

line->installSceneEventFilter(ellipse);
// line's events are filtered by ellipse's sceneEventFilter() function.

ellipse->installSceneEventFilter(line);
// ellipse's events are filtered by line's sceneEventFilter() function.
//! [12]


//! [13]
void CustomItem::contextMenuEvent(QGraphicsSceneContextMenuEvent *event)
{
    QMenu menu;
    QAction *removeAction = menu.addAction("Remove");
    QAction *markAction = menu.addAction("Mark");
    QAction *selectedAction = menu.exec(event->screenPos());
    // ...
}
//! [13]


//! [14]
CustomItem::CustomItem()
{
    setAcceptDrops(true);
    ...
}

void CustomItem::dragEnterEvent(QGraphicsSceneDragDropEvent *event)
{
    event->setAccepted(event->mimeData()->hasFormat("text/plain"));
}
//! [14]


//! [15]
QVariant Component::itemChange(GraphicsItemChange change, const QVariant &value)
{
    if (change == ItemPositionChange && scene()) {
        // value is the new position.
        QPointF newPos = value.toPointF();
        QRectF rect = scene()->sceneRect();
        if (!rect.contains(newPos)) {
            // Keep the item inside the scene rect.
            newPos.setX(qMin(rect.right(), qMax(newPos.x(), rect.left())));
            newPos.setY(qMin(rect.bottom(), qMax(newPos.y(), rect.top())));
            return newPos;
        }
    }
    return QGraphicsItem::itemChange(change, value);
}
//! [15]


//! [16]
void CircleItem::setRadius(qreal newRadius)
{
    if (radius != newRadius) {
        prepareGeometryChange();
        radius = newRadius;
    }
}
//! [16]


//! [17]
// Group all selected items together
QGraphicsItemGroup *group = scene->createItemGroup(scene->selecteditems());

// Destroy the group, and delete the group item
scene->destroyItemGroup(group);
//! [17]


//! [18]
class QGraphicsPathItem : public QAbstractGraphicsShapeItem
{
 public:
  enum { Type = 2 };
    int type() const override { return Type; }
  ...
};
//! [18]

//! [19]
QTransform xform = item->deviceTransform(view->viewportTransform());
QRect deviceRect = xform.mapRect(rect).toAlignedRect();
view->viewport()->scroll(dx, dy, deviceRect);
//! [19]

//! [20]
item->setTransform(QTransform().rotate(angle), true);
//! [20]

//! [21]
setTransform(QTransform::fromScale(sx, sy), true);
//! [21]

//! [22]
setTransform(QTransform().shear(sh, sv), true);
//! [22]

//! [23]
setTransform(QTransform::fromTranslate(dx, dy), true);
//! [23]