[Qt-interest] real time strip chart

[Atlant Schmidt]

Giovanni:

> > > It is too slow. ... Incoming data are faster than one
> > > sample for pixel,
> >
> >   I'm not sure I understood this correctly, but what I think
> >   you're saying here is that each "column" of your strip-chart
> >   output can contain multiple samples *FROM EACH CHANNEL*
> >   because the overall time that each column represents is longer
> >   than the sample interval of the data so you get (say) ten samples
> >   from each channel being displayed in the same column.
>
> exactly this way

  Thanks for clarifying that.


> In fact my problem is not to draw the traces and scroll
> the image in main memory (it takes about 2msec (real time
> and CPU time)) on the 20msec available, but to copy it
> on the screen.

  Of course. Without a doubt, the CPU takes tremendous
  advantage of all of the caching going on, but to get
  the data to the frame buffer, something still has to
  do real I/O (external bus) operations and these haven't
  increased in speed nearly as much as CPU (or GPU!)
  internal operations have. The key is to convince the
  GPU to do the scrolling for you and only draw the
  newest column. Easy trick, right? ;-)

                               Atlant


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