[Qt-interest] Qt Charting Component - Feedback Request

[Sean Harmer]

Hi,

On Tuesday 08 March 2011 12:45:49 Uwe Rathmann wrote:
> Hi Sean,
> 
> > I simply wanted to try a different approach and
> > to base it on QGraphicsView ...
> 
> Well QGraphicsView is some sort of "middleware" sitting on top of QPainter.
> Using it is probably the easier way - in the beginning - but not the light-
> weight ( as you wrote ) one. Especially, when you are using an item for each
> point it is the slowest and most memory consuming approach I can imagine (
> think about 10e6 QObjects ! ) for large curves. But for non technical plots
> ( like business charts ) this shouldn't matter.

I have this for business type plots to enable easy customisation of individual 
points as you say. However, for large scale plots I just use a single 
QGraphicsItem to plot all the points in that series so it reduces down close 
the way Qwt uses QPainter. 

I have not looked in detail at what caching Qwt does so I cannot comment on 
that aspect but QGV does provide a reasonable interface for caching items that 
need to be repainted regularly.

I meant light-weight as compared to having widgets for each plot-element. I 
know this is not how Qwt is structured.

I have even longer term ideas to even separate this from QGV and to use an 
OpenGL based scene graph backend. That is way out in the future though. I 
wanted to get some experience with typical plotting features using a 
comfortable middleware API like QGV first.

> Nevertheless your design has several pros - f.e. I often have request, where
> users want to manipulate points with the mouse. And to be honest I would
> love to have the separation of scene and view in Qwt too - hope I will find
> the time some day.

Time is always the limiting factor. Not enough hours in the day. ;-)

> Good luck,

Thank you, and to you too.

Sean