Trying to overlay widget on a QTreeView item

I'm trying to align a rectangle over the text portion of a QTreeView item. Calculating the rectangle is a bit complicated because the checkbox indents add up depending on the number of parents, etc.

So to debug this I figured I'd just draw a physical rectangle over the math prediction. However, I'm unable to render a QWidget on top of a tree view item. It never shows up. Any ideas what's wrong or how to overlay a visual over a QTreeView item?

Basically, I want to see something like this, so I can tell where my textRect calc is off.

Attachment 13428

My attempt below. I'm trying to draw the rectangle in the treeview's mousePressEvent. But, no matter what I do, the overlay widget never appears...

Code:

---

void TreeView::mousePressEvent (QMouseEvent *event)
{
    if (event->button() == Qt::LeftButton)
    {
        QRect textRect = QRect(checkboxX
                               + style()->pixelMetric(QStyle::PM_IndicatorWidth)
                               + style()->pixelMetric(QStyle::PM_CheckBoxLabelSpacing)
                               + 30 // color chip and padding
                               + 3, // little padding
                               vrect.y(),
                               treeItemWidth,
                               vrect.height());
 
        // Overlay colored widget to see the rectangle
        PaintWidget *overlay = new PaintWidget(textRect, this);
        overlay->repaint(); // try to force the repaint
 
    }

---

Code:

---

class PaintWidget : public QWidget
{
    Q_OBJECT
 
public:
    explicit PaintWidget(const QRect &paintArea, QWidget *parent=nullptr)
        : QWidget(parent), m_area(paintArea)
        {
            setGeometry(m_area);
            QPalette pal = palette();
            // set white background
            pal.setColor(QPalette::Background, Qt::white);
            setPalette(pal);
            this->update();
        }
    ~PaintWidget(){};
 
private:
    QRect m_area;
};

---

You cannot do any on-screen painting anywhere except in a paintEvent().

I think you can probably accomplish what you want with a QStyledItemDelegate. All of the geometry calculations are made for you. Take a look at the Star Delegate example.

You might also be able to do this by adding additional cases to your QAbstractItemModel::data() method to handle the Qt::BackgroundRole.

Thanks d_stranz, after some more attempts here's the working code.

Code:

---

#include <QPaintEvent>
#include <QPainter>
#include <QDebug>
class PaintWidget : public QWidget
{
    Q_OBJECT
 
public:
    explicit PaintWidget(const QRect &paintArea, QWidget *parent=nullptr)
        : QWidget(parent), m_area(paintArea)
        {
            setAttribute(Qt::WA_NoSystemBackground);
            setAttribute(Qt::WA_TransparentForMouseEvents);            
        }
    ~PaintWidget(){};
 
protected:
    void paintEvent(QPaintEvent */*event*/) override
    {
        QPainter(this).fillRect(m_area, {255, 0, 0, 100});
    }
private:
    QRect m_area;
};

---

And the calling function I resize the overlay widget to be the entire size of the treeview, but only paint the rectangle of interest.

Code:

---

PaintWidget *overlay = new PaintWidget(textRect, this);
overlay->resize(this->width(), this->height());
overlay->show();

---