Re: calling setPen for each symbol

On Thursday 08 October 2009 07:04, Paul Harris wrote:

> An example usage... X-Y chart with markers.  On the bottom axis, voltage.
> On the Y axis, current.  The colour corresponds to the time that the
> reading was taken.  Colour is a continuous spectrum from blue to red.

A 3D curve representing the 3rd dimension as color is on my TODO list for Qt 
5.3. ( Guess something about 1-2 hours of work ).

> Or, I might hack the basic datatype to add in a virtual color() call.  That
> wouldn't be too hard.

Use a QwtColorMap - it is made for mapping values to colors.

> Ideally I'll subclass qwt_plot_curve, but it may not be structured in the
> best way for subclassing (I'll have to figure that out later).

Consider to use a 5.3 snapshot (= trunk), where you find the QwtPlotSeriesItem 
template, what is exactly what you are looking for.

> The real question is, does changing the pen colour all the time affect
> performance?   

No, the real question is: how do you reduce the number of points you need to 
paint according to the current zoom level. 

Uwe

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