Overriding drawRubberBand()

[andrew.nguyen]

Hi all,

I am brand new to Qwt and am currently trying to override drawRubberBand() so that I can have a semi-transparent, gray rubberband. My initial inclination was to override drawRubberBand() and set some of the parameters of QPainter (e.g. opacity, brush).

However, it's not working as I've expected. From initial debugging, it seems the problem is with the updateMask() function conflicting with what I want to do. I noticed that it's a virtual function but don't know if it's possible to override a virtual function of a private inner class.

Is there a better way to accomplishing my goal of having an semi-transparent, filled rectangle as a rubberband?

As a related issue, I would also like the rectangle to persist until a new rectangle is selected.

Thanks!

[Uwe]

My initial inclination was to override drawRubberBand() and set some of the parameters of QPainter (e.g. opacity, brush).

This should be the right idea - simply set a brush and call drawRubberBand() from the base class. Use your semitransparent brush, when the painter is connected to a widget and use Qt::color1, when it is connected to a QBitmap ( = updateMask ).

As a related issue, I would also like the rectangle to persist until a new rectangle is selected.

You need to implement a new type of plot item. Have a look at the RectItem of the navigation example in SVN trunk: http://qwt.svn.sourceforge.net/viewv...02&view=markup. Update + show the RectItem after your picker has selected an area and hide it, when your picker start selecting.

Uwe

[andrew.nguyen]

For the semitransparent rubber band, what is the best mechanism for determining if the painter is connected to a widget? The only thing I can think of is dynamic casting but that would be slow if called everytime drawRubberBand is called... Or, am I just totally off base?

[Uwe]

Yes you are: avoiding a dynamic cast is the last thing that is of relevance in this context.

Uwe