form::form(QWidget *parent) : QMainWindow(parent)
{
    setMinimumSize(200, 180);
    centralwidget = new QWidget(this);
    setCentralWidget(centralwidget);

    QTextEdit *textedit = new QTextEdit(centralwidget);
    QPushButton *btn = new QPushButton("text", textedit);

    QVBoxLayout *vl = new QVBoxLayout(centralwidget);
    vl->addWidget(textedit);
    vl->addWidget(btn);

    centralwidget->setLayout(vl);

    centralwidget->installEventFilter(this);
    textedit->viewport()->installEventFilter(this);
    btn->installEventFilter(this);
}


bool form::eventFilter(QObject *obj, QEvent *event)
{
    if(event->type() == QEvent::Paint) {
        obj->removeEventFilter(this);
        QApplication::sendEvent(obj, event);
        obj->installEventFilter(this);

        QPainter p(qobject_cast<QWidget*>(obj));
        p.setPen(Qt::red);
        p.setViewport(rect());
        p.drawLine(rect().topLeft(), rect().bottomRight());
        return true;
    }
    return false;
}

#include <QtCore/QEvent>
#include <QtCore/QTimer>
#include <QtGui/QTextEdit>
#include <QtGui/QGridLayout>
#include <QtGui/QVBoxLayout>
#include <QtGui/QPainter>
#include <QtGui/QApplication>
#include <QtGui/QPushButton>
#include <QtDebug>

#include "form.h"

form::form(QWidget *parent) : QMainWindow(parent)
{
    setMinimumSize(200, 180);
    centralwidget = new QWidget(this);
    centralwidget->setObjectName("centralwidget");
    setCentralWidget(centralwidget);

    QTextEdit *textedit = new QTextEdit(centralwidget);
    textedit->setObjectName("textedit");
    QPushButton *btn = new QPushButton("text", this);
    btn->setObjectName("btn");

    QVBoxLayout *vl = new QVBoxLayout(centralwidget);
    vl->addWidget(textedit);
    vl->addWidget(btn);

    centralwidget->setLayout(vl);

    centralwidget->installEventFilter(this);
    textedit->viewport()->installEventFilter(this);
    btn->installEventFilter(this);
}


bool form::eventFilter(QObject *obj, QEvent *event)
{
    if(event->type() == QEvent::Paint) {
        obj->removeEventFilter(this);
        QApplication::sendEvent(obj, event);
        obj->installEventFilter(this);

//        qDebug()<< qobject_cast<QWidget*>(obj)
  //              << qobject_cast<QWidget*>(obj)->geometry()
    //            <<" "
    //            << qobject_cast<QWidget*>(obj)->visibleRegion();

        QPainter p(qobject_cast<QWidget*>(obj));
        p.setPen(Qt::red);
        if(qobject_cast<QWidget*>(obj)->objectName() == "qt_scrollarea_viewport")
            p.setWindow(centralwidget->findChild<QTextEdit*>("textedit")->geometry());
        else
        p.setWindow(qobject_cast<QWidget*>(obj)->geometry());
        p.drawLine(rect().topLeft(), rect().bottomRight());
        return true;
    }
    return false;
}

bool form::eventFilter(QObject *obj, QEvent *event)
{
    if(event->type() == QEvent::Paint) {
        obj->removeEventFilter(this);
        QApplication::sendEvent(obj, event);
        obj->installEventFilter(this);

        QWidget *widget = qobject_cast<QWidget*>(obj);
        QPoint point = widget->pos();
        while(widget && (widget->parentWidget() != this)) {
            widget = widget->parentWidget();
            point += widget->pos();
        }

        QRect r = qobject_cast<QWidget*>(obj)->rect().translated(point);

        QPainter p(qobject_cast<QWidget*>(obj));
        p.setPen(Qt::red);
        p.setWindow(r);

        p.drawLine(rect().topLeft(), rect().bottomRight());
        return true;
    }
    return false;
}