QwtPlot: data points appear in blocks

Hi,

I am using QwtPlot to plot data points that are generated by a computer model that is executed in a thread of its own. I was doing some tests with a simulation that generates 1,000,000 data points. I have three different graphs, all using one-pixel wide curves (with antialiasing), and it all goes nice and smooth. Then, I thought I would repeat the exact same simulation, but this time with two-pixel wide curves. This time, however, the plotting is really sketchy. In fact, the data points appear in big blocks. Just to confirm my doubts, I repeated the simulation with three-pixel wide curves, and it was the same, i.e. the data points appear in big blocks.

Here is a small movie that shows the issue I am facing. Basically, with two- and three-pixel curves, it takes much longer to QwtPlot to render the data points, and during that time many more data points have been generated (since their generation is done in a different thread), hence the data points appearing in blocks. If I (programatically) slow down the simulation, everything is smooth again, but this is clearly not something I want to do.

So, is there any way to make the rendering smoother, no matter the width of the curves, or am I out of luck here?

Cheers, Alan.