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Window::Window()
{
    setWindowTitle(tr("OpenGL"));

    GLWidget *openGL = new GLWidget(&helper, this);
    this->setFixedSize(300,300);
    openGL->resize(this->width(),this->height());

    QTimer *timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), openGL, SLOT(animate()));
    timer->start(1);
}

void GLWidget::animate()
{
    elapsed = (elapsed + qobject_cast<QTimer*>(sender())->interval()) % 10;
    update();
}

void GLWidget::paintEvent(QPaintEvent *event)
{
    QPainter painter;
    painter.begin(this);
    painter.setRenderHint(QPainter::Antialiasing);
    helper->paint(&painter, event, elapsed);
    painter.end();
}

void Helper::paint(QPainter *painter, QPaintEvent *event, int elapsed)
{

    painter->fillRect(event->rect(), background);
    QPen penRect(Qt::black);
    penRect.setWidth(2);
    painter->setPen(penRect);
    painter->drawRect(GL_WINDOW_MIN_SIZE.x(),GL_WINDOW_MIN_SIZE.y(),GL_WINDOW_MAX_SIZE.x(),GL_WINDOW_MAX_SIZE.y());
    painter->setViewport(0,0,300,300);
    painter->save();

    if (CheckPaint == 0)
    {
        painter->setBrush(circleBrush);
        painter->setPen(circlePen);
        painter->drawEllipse(CircleCoord.x(),CircleCoord.y(),
                             CircleSize.x(),CircleSize.y());
        CheckPaint = 1;
    }
    else if (CheckPaint == 1)
    {
        painter->setBrush(clearCircleBrush);
        painter->setPen(clearCirclePen);
        painter->drawEllipse(CircleCoord.x(),CircleCoord.y(),
                             CircleSize.x(),CircleSize.y());
        CheckPaint = 0;
        ChangeCoord();

    }
    painter->restore();
}

void Helper::ChangeCoord()
{
    CircleCoord.setX(CircleCoord.x()+CircleStep.x());
    CircleCoord.setY(CircleCoord.y()+CircleStep.y());

    if (CircleCoord.x() < GL_WINDOW_MIN_SIZE.x())
    {
        CircleStep.setX(-CircleStep.x());
        CircleCoord.setX(GL_WINDOW_MIN_SIZE.x() - (CircleCoord.x() - GL_WINDOW_MIN_SIZE.x()));
    }
    if (CircleCoord.y() < GL_WINDOW_MIN_SIZE.y())
    {
        CircleStep.setY(-CircleStep.y());
        CircleCoord.setY(GL_WINDOW_MIN_SIZE.y() - (CircleCoord.y() - GL_WINDOW_MIN_SIZE.y()));
    }
    int bufMaxX = GL_WINDOW_MAX_SIZE.x()-CircleSize.x();
    int bufMaxY = GL_WINDOW_MAX_SIZE.y()-CircleSize.x();
    if (CircleCoord.x() > bufMaxX)
    {
        CircleStep.setX(-CircleStep.x());
        CircleCoord.setX(CircleCoord.x() - (CircleCoord.x()- bufMaxX ));
    }
    if (CircleCoord.y() > bufMaxY)
    {
        CircleStep.setY(-CircleStep.y());
        CircleCoord.setY(CircleCoord.y() - (CircleCoord.y() - bufMaxY));
    }
}