I have noticed that QPainter::drawText is horribly slow on Linux when using it with a scaled window mapping. Is there anything I can do about this? I already checked whether disabling anti-aliasing or enabled the raster-renderer makes a difference, but it doesn't.

Example: When using a viewport size of (450px, 200px), a window size of factor 100 (45000, 20000) and thus font sizes scaled up by factor 100 as well (1400pt), rendering 30 times the text "hello" takes about 4(!) seconds on Linux - both on OpenSuse and Ubuntu.

The same sample renders in a snap on Windows and Mac.

Just for clarification: although the font size is scaled up, the text appears in "normal" size on screen due to the described window<->viewport mapping.

Here is the simple sample code I am using:

void Widget::paintEvent(QPaintEvent *event)
{
    const int scaleFactor = 100;

    QPainter painter(this);

    // Setup font
    QFont font;
    font.setPointSize(14*scaleFactor);
    painter.setFont(font);

    // Setup mapping
    painter.setWindow(0, 0, width() * scaleFactor, height() * scaleFactor);

    // Render the text
    for (int i = 0; i < 30; i++)
        painter.drawText(qrand() % (width() * scaleFactor), qrand() % (height() * scaleFactor), "Hello");
}

Any help would be awesome.

Note: I am using Qt 4.8.5