Qt4.8 окрашивание половины кнопки

#ifndef BTN_H
#define BTN_H

#include <QPushButton>
#include <QLinearGradient>
#include <QPainter>

class Btn : public QPushButton {
public:
    Btn(QWidget *parent = nullptr);

protected:
    void paintEvent(QPaintEvent *e) override;
};

#endif

#include <btn.h>

Btn::Btn(QWidget *parent) : QPushButton(parent)
{
}

void Btn::paintEvent(QPaintEvent *e)
{
    QPainter p(this);
    
    QLinearGradient grad(width()/2, 0, width()/2, height());
    grad.setColorAt(0, Qt::red);
    grad.setColorAt(1, Qt::green);

    p.setBrush(grad);
    p.drawRect(rect());
}