[Interest] Draw ellipse (and etc.) the same way as cosmetic QPen

[Ian Thomson]

Have you tried adding child GraphicsItems for each of the dots and
setting the flag QGraphicsItem::ItemIgnoresTransformations? That should
do the trick.

Ian.


On 14/01/14 12:11, Dmitrii Volosnykh wrote:
> Is there a possibility to draw something irrespectively to scene
> transformations such as cosmetic QPen?
>
> I've tried to approaches but none brings me to a success. I have some
> scene that may contain a polyline with vertices represented by bold
> dots. While polyline and thus coordinates of dots should respect scene
> scaling, I don't want the size of dots to change.
>
> Here's the Polyline's imlementation of paint() method (Polyline inherits
> QGraphicsPolygonItem):
>
> void PolylineItem::paint(QPainter* const painter, const
> QStyleOptionGraphicsItem* const option, QWidget* const widget)
> {
>      Q_UNUSED(option);
>      Q_UNUSED(widget);
>
>      painter->setPen(pen());
>      painter->setBrush(brush());
>
>      painter->drawPolyline(polygon());
>
> #if 0
>      if (polygon().size() > m_points.size()) {
>          for (int i = m_points.size(); i < polygon().size(); ++i) {
>              auto* const point = new QGraphicsEllipseItem(this);
>              point->setPen(pen());
>              point->setBrush(brush());
> //            point->setFlag(QGraphicsItem::ItemIgnoresTransformations);
>              m_points.append(point);
>          }
>      } else if (polygon().size() < m_points.size()) {
>          const int count = m_points.size() - polygon().size();
>          for (int i = 0; i < count; ++i) {
>              delete m_points.takeLast();
>          }
>      }
>
>      const qreal r = pen().widthF() * POINT_RADIUS_RATIO;
>      for (int i = 0; i < m_points.size(); ++i) {
>          const QPointF& c = polygon().at(i);
>          m_points[i]->setRect(c.x() - r, c.y() - r, 2 * r, 2 * r);
>      }
> #else
>      const qreal r = pen().widthF() * POINT_RADIUS_RATIO;
>      foreach (const QPointF& point, polygon()) {
>          painter->drawEllipse(point, r, r);
>      }
> #endif
> }
>
> The code between #else and #endif directives is the first
> straightforward way I've tried. The points are scaled in size.
> The part between #if and #else behaves the same when point->setFlag() is
> commented out. If I enable this invokation, the points are constantly of
> the same size, as I want it, but their positions are scaled outside the
> polyline. In fact, they are not scaled, but the whole scene with the
> polyline itself are scaled, so it looks like the dots are moving outside.
>
> Can't figure out what to do. Asking for help.
>
> Regards,
> Dmitrii.
>
>
> _______________________________________________
> Interest mailing list
> Interest at qt-project.org
> http://lists.qt-project.org/mailman/listinfo/interest
>


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