// do clipping if neccesary on specific systems
int count = curveData->size();
if (!canvas()->testAttribute(Qt::WA_PaintOnScreen)){
    // Depending on the platform setting a clip might be an important
    // performance issue. F.e. for Qt Embedded this reduces the
    // part of the backing store that has to be copied out - maybe
    // to an unaccelerated frame buffer device.
    const QwtScaleMap xMap = canvasMap(mActive->xAxis());
    const QwtScaleMap yMap = canvasMap(mActive->yAxis());

    // get bounding rect
    QRectF boundingRect = qwtBoundingRect(*curveData, (curveData->size() - points.size()) - 1, count - 1);
    const QRect clipRect = QwtScaleMap::transform(xMap, yMap, boundingRect).toRect();
    mDirectPainter->setClipRegion(clipRect);
}

// use the direct painter and paint the entire line
// this is still much faster than a 'replot'
mDirectPainter->drawSeries(mActive, (count - points.size()) - 1, count);

}
@

Everything works great and is extremely efficient! up until two points right next to each other on the graph have a drastic change in x value on the plot (.001mS apart on a 20 second x scale). The curve seems to not want to paint in between the two points which I think is due to the clipping region.

I guess my real question is, how does the clipping work? I haven't really used much manual painting in Qt in general. Here http://imgur.com/8Vy4Xzz is an image of the graph for a visual example what is happening.

Edit: My issue is somewhat solved. I increased the clipping region to the size of the canvas and now there are no plot points missing during the direct paint.