title: QWT: Replot without removing the previous points
body: <p>I am using QWT 6 and I am trying to plot some dots every second. To do that I use the following code:</p>
  
  <pre><code>d_plot_dots-&gt;setRawSamples(_realDataPoints, _imagDataPoints, size);
  plot-&gt;replot();
  </code></pre>
  
  <p>I want to support a hold on option, so dots from previous seconds to be still visible at the plot. One solution to this is to resize every second the arrays that hold the points, append the new values and call again the <code>setRawSamples()</code> and the <code>replot()</code>, but this solution is not memory efficient as at every seconds I have to store at least 2 * 2048 points.</p>
  
  <p>Is there any, more efficient way?
  Thanks in advance!</p>