QT实现多次绘制--双缓冲机制

1、源代码如下：

void Kmeans::drawPoint()
{
    QPicture pp;
    painterP.begin(&pp);//开始记录
    pp.setBoundingRect(ui.label_2->rect());
    painterP.setRenderHint(QPainter::Antialiasing, true);

    Pointp p1;
    p1.no = p.at(0).no;
    p1.x = p.at(0).x;
    p1.y = p.at(0).y;
    for (int i = 1; i < p.size(); i++)
    {
        if (p1.x > p.at(i).x)
        {
            p1.x = p.at(i).x;
        }
        if (p1.y > p.at(i).y)
        {
            p1.y = p.at(i).y;
        }
    }
    double xmin = p1.x;
    double ymin = p1.y;

    for (int i = 1; i < p.size(); i++)
    {
        if (p1.x < p.at(i).x)
        {
            p1.x = p.at(i).x;
        }
        if (p1.y < p.at(i).y)
        {
            p1.y = p.at(i).y;
        }
    }
    double xmax = p1.x;
    double ymax = p1.y;

    int w=ui.label_2->width();
    int h=ui.label_2->height();

    double a = w/(xmax -xmin);
    double b1 = h/(ymax -ymin);

    for (int i = 0; i < k.size(); i++)
    {
        int r = qrand() % 256;
        int g = qrand() % 256;
        int b = qrand() % 256;
        QColor color = QColor(r, g, b);

        for (int j = 0; j < S.size(); j++)
        {
            if (k.at(i).no == S.at(j).noK)
            {
                pen.setColor(color);
                painterP.setPen(pen);
                int radius = 5;
                double x = S.at(j).x;
                double y = S.at(j).y;
                x = (x - xmin)*a;
                y = (y - ymin)*b1;
                painterP.drawEllipse(x - radius, y - radius, radius * 2, radius * 2);
            }
        }
    }
    painterP.end();//记录绘制过程结束
    ui.label_2->setPicture(pp);
}