src_gui_graphicsview_qgraphicsitem.cpp

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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);
    }
};
 
 
class CustomItem : public QGraphicsItem
{
public:
   enum { Type = UserType + 1 };
 
   int type() const override
   {
       // Enable the use of qgraphicsitem_cast with this item.
       return Type;
   }
   ...
};
 
 
item->setCursor(Qt::IBeamCursor);
 
 
item->setCursor(Qt::IBeamCursor);
 
 
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);
 
 
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
 
 
// 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));
 
 
// 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));
 
 
QRectF CircleItem::boundingRect() const
{
    qreal penWidth = 1;
    return QRectF(-radius - penWidth / 2, -radius - penWidth / 2,
                  diameter + penWidth, diameter + penWidth);
}
 
 
QPainterPath RoundItem::shape() const
{
    QPainterPath path;
    path.addEllipse(boundingRect());
    return path;
}
 
 
void RoundRectItem::paint(QPainter *painter,
                          const QStyleOptionGraphicsItem *option,
                          QWidget *widget)
{
    painter->drawRoundedRect(-10, -10, 20, 20, 5, 5);
}
 
 
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");
}
 
 
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.
 
 
void CustomItem::contextMenuEvent(QGraphicsSceneContextMenuEvent *event)
{
    QMenu menu;
    QAction *removeAction = menu.addAction("Remove");
    QAction *markAction = menu.addAction("Mark");
    QAction *selectedAction = menu.exec(event->screenPos());
    // ...
}
 
 
CustomItem::CustomItem()
{
    setAcceptDrops(true);
    ...
}
 
void CustomItem::dragEnterEvent(QGraphicsSceneDragDropEvent *event)
{
    event->setAccepted(event->mimeData()->hasFormat("text/plain"));
}
 
 
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);
}
 
 
void CircleItem::setRadius(qreal newRadius)
{
    if (radius != newRadius) {
        prepareGeometryChange();
        radius = newRadius;
    }
}
 
 
// Group all selected items together
QGraphicsItemGroup *group = scene->createItemGroup(scene->selecteditems());
 
// Destroy the group, and delete the group item
scene->destroyItemGroup(group);
 
 
class QGraphicsPathItem : public QAbstractGraphicsShapeItem
{
 public:
  enum { Type = 2 };
    int type() const override { return Type; }
  ...
};
 
QTransform xform = item->deviceTransform(view->viewportTransform());
QRect deviceRect = xform.mapRect(rect).toAlignedRect();
view->viewport()->scroll(dx, dy, deviceRect);
 
item->setTransform(QTransform().rotate(angle), true);
 
setTransform(QTransform::fromScale(sx, sy), true);
 
setTransform(QTransform().shear(sh, sv), true);
 
setTransform(QTransform::fromTranslate(dx, dy), true);