[Qt-interest] Qt Charting Component - Feedback Request

[Sean Harmer]

Hi,

On Saturday 05 March 2011 07:26:26 Syam Krishnan wrote:
> On 03/04/2011 09:19 PM, Sean Harmer wrote:
> > Hi All,
> > 
> > I've started work on a charting component for Qt. I have posted some
> > details
> 
> > of it along with code snippets on the Qt DevNet:
> Wow.. The screenshots do look great.

Thank you to you and all others for your kind words.

> > I would like to ask those of you on this list if there is interest in
> > such a charting component and to ask you for feedback on the API and
> > features that I have in place so far. I am also open to feature
> > requests - although no promises of an implementation at this stage.
> 
> I'm very much interested in a good charting component. We've been trying
> out Qwt, but it seems to have some performance problems when used with
> larger changing datasets.

Yes I have this requirement too.

> Our requirement often is plotting of continuous data. i.e. a new data
> point is available every 100 or 200 ms. Adding these points to the plot
> should be as light-weight an operation as possible. As far as I can see,
> the current Qwt implementation requires copying the entire point list
> again and re-plotting from the beginning. This consumes a lot of CPU.
> I'd love to see an implementation where incremental plotting is super-fast.

My planned approach is to implement a special ZAbstractDataSet (my interface 
between the graphical plots and user data) subclass based upon a circular 
buffer especially for this use case. This would make appending new data an 
O(1) operation. It essentially bypasses the copying that is involved in doing 
this in Qwt (I have also suffered from this). The QGraphicsView framework also 
makes it possible to only redraw those items affected too.

I'll try to get this into the initial release.

Thanks for the request,

Sean