Qt, particle system and additive blending

black_gay

I’m creating a particle system using Qt and c++. I want to blend colours of the particles that overlap each other – adding the RGB values on top of each other, so colours would get brighter, something like this:
Desired effect
My code looks like this:

In custom QGraphicsScene class:
    QPixmap* pixmap2 = new QPixmap("E:\\Qt_workspace\\1\\smoke5.png");
    pixmap2->setDevicePixelRatio(0.5);
    QPointF origin2 = {250, 100};
    QPainter pix2(pixmap2);
    pix2.setCompositionMode(QPainter::CompositionMode_Plus);
    pix2.drawPixmap(origin2, *pixmap2);
    pix2.setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform, true);
    particleSystem2 = new ParticleSystem(this, pixmap2, origin2);
    v_particleSystem.push_back(particleSystem2);

And i create particles in a loop:

void Level1::advance()
{
    for (int i = 0; i < v_particleSystem.size(); ++i) {
        v_particleSystem\[i\]->applyForce(gravity);
        QVector2D v = { (float)player->x(), (float)player->y() };
        repeller->update(v);
        v_particleSystem[i]->applyReppeler(repeller);
 
        v_particleSystem[i]->addParticle();
        v_particleSystem[i]->run();
    }
    update(sceneRect); ///so items dont leave any artifacts though works without it when 
using m_view->viewport()->repaint();
    m_view->viewport()->repaint();

And Particle class derives from QGraphicsPixmapItem.
But im getting this result:
Achieved effect
Any idea how to achieve additive blending?