Drawing an overlay on top of an application's window

Question

I want to be able to paint on top of my application\'s window so that I can annotate all the widgets with some extra diagnostic information, similar to the CSS developer too

Answer 1

Somewhere in Qt5 the styles (GTK, Windows, etc) were made internal. Now you need to use QCommonStyle.

If anyone's wondering how to do this with Qt5+. Here's a self-contained version of @the_mandrill's code above.

class DiagnosticStyle : public QCommonStyle
{
Q_OBJECT

public: 
    typedef QStyle BaseStyle;
    void drawControl(ControlElement element, const QStyleOption* option, QPainter* painter, const QWidget* widget) const
    {
        QCommonStyle::drawControl(element, option, painter, widget);
        if (widget && painter) {
            // draw a border around the widget
            painter->setPen(QColor("red"));
            painter->drawRect(widget->rect());

            // show the classname of the widget
            QBrush translucentBrush(QColor(255,246,240, 100));
            painter->fillRect(widget->rect(), translucentBrush);
            painter->setPen(QColor("darkblue"));
            painter->drawText(widget->rect(), Qt::AlignLeft | Qt::AlignVCenter, widget->metaObject()->className()); 
        }
    };
};

Then, in your main window constructor call

qApp->setStyle(new DiagnosticStyle());