Custom QRubberBand with transparent background

[mdomke]

Hi,

as already discussed here and here it should be possible to paint modify the appearance of the QRubberBand by making a subclass and overwriting the paintEvent. The rubberband should be displayed on QGraphicsView to select some items on a QGraphicsScene. I'm able to modify the frame color but the background of the rubber band rect remains completely transparent (white). Here is my implementation of the QRubberBand subclass

#include "SelectionFrame.h"
#include <QPaintEvent>
#include <QPainter>
#include <QDebug>
 
SelectionFrame::SelectionFrame(Shape shape, QWidget *parent) :
    QRubberBand(shape, parent)
{
    _border_color = QColor(0, 83, 235);
    _background_color = QColor(51, 122, 255);
}
 
SelectionFrame::~SelectionFrame()
{
}
 
void SelectionFrame::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event);
 
    QPainter painter;
    QPen pen = QPen(_border_color);
    pen.setWidth(5);
    pen.setStyle(Qt::DashLine);
 
    QBrush brush = QBrush(_background_color);
 
    painter.begin(this);
    painter.setPen(pen);
    painter.setOpacity(0.5);
    painter.setBrush(brush);
    painter.drawRect(event->rect());
    painter.end();
}

#include "SelectionFrame.h"
#include <QPaintEvent>
#include <QPainter>
#include <QDebug>

SelectionFrame::SelectionFrame(Shape shape, QWidget *parent) :
    QRubberBand(shape, parent)
{
    _border_color = QColor(0, 83, 235);
    _background_color = QColor(51, 122, 255);
}

SelectionFrame::~SelectionFrame()
{
}

void SelectionFrame::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event);

    QPainter painter;
    QPen pen = QPen(_border_color);
    pen.setWidth(5);
    pen.setStyle(Qt::DashLine);

    QBrush brush = QBrush(_background_color);

    painter.begin(this);
    painter.setPen(pen);
    painter.setOpacity(0.5);
    painter.setBrush(brush);
    painter.drawRect(event->rect());
    painter.end();
}

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As the painter's pen has been set to dashed, I think I can see, that there is an additional border painted on top of the dashed line with the correctly set transparency. The background is however not painter. Does anyone have a suggestion how this can be done right?

[mdomke]

I thin I remained a little bit unclear about what I'm trying to achieve. The rubber bands background (the content of the selection rectangle) should be semi-transparent and have a special color. In my understanding the rubber bands default behavior, at least on my system, is to have a completely transparent content area with only the borders painted.