Re: qwt plot and scrollbars

[<s.c...@gm...>]

Hello,

I did something like that... but not using Qwt and C++ but using
Visual Basic 6 (shame on me !
but we use this at work !) and PictureBox control.
I first did a circular buffer class that had
a addItem(double value) method
http://en.wikipedia.org/wiki/Circular_buffer
It puts a value in a the reserved space of memory. When the memory
reserved is full it overwrite the oldest value.
This class also contain a private integer index to know where the
value must be store.
This class also have a method to get values : fromLastest(int index)
FromLast(0) to get the latest value
FromLast(1) to get the latest-1 value

I use this circular buffer class in the plot object to store all the values.

I use also use an integer value that belongs to the intervall 0 ;
buffer.Capacity - window_capacity
buffer.Capacity is the number of points in the circular buffer
window_capacity is the number of points that can be shown in a "window"
this integer value is used to know that part of the value need to be draw.

You can find VB6 source code to get some API ideas at
http://svn.berlios.de/viewcvs/openphysic/vb/vb6/phys/plot_scroll_window/
You can just have a look at source code using the SVN viewer

If you want to do it in a clean C++ coding style you could maybe use
the Boost implementation of circular buffer
http://www.boost.org/doc/libs/1_38_0/libs/circular_buffer/doc/circular_buffer.html

I hope this will help you

I'm alway thinking (I talked about it some days ago) that a widget
inherited from QwtPlot that cointains all this could be usefull
but I'm not C++ developper (I'm just a little better than a beginer..)


Kind regards

On Tue, Mar 10, 2009 at 7:49 PM, Darryl Wallace
<dar...@pr...> wrote:
> Check out the realtime plot example that comes with Qwt.  It shows how
> to make a "ScrollZoomer" but that may help point you in the right direction.
>
> It'd be kind of a hack but you could implement the scrollzoomer, and
> then when your data is added you can update the zoomRect.  Or something
> along those lines.
>
> darryl
>
> Giacomo S. wrote:
>> Good morning.
>>
>> Is there a simple way to make my QwtPlot have the horizontal scrollbar
>> automatically shown when the x data vector size reaches a certain value?
>>
>> For instance, when I have 200 elements in the x axis, I want the plot to
>> enable scrolling.
>>
>> Thanks in advance
>>
>> Giacomo.
>>
>>
>> ------------------------------------------------------------------------------
>> _______________________________________________
>> qwt-interest mailing list
>> qwt...@li...
>> https://lists.sourceforge.net/lists/listinfo/qwt-interest
>>
>
> ------------------------------------------------------------------------------
> _______________________________________________
> qwt-interest mailing list
> qwt...@li...
> https://lists.sourceforge.net/lists/listinfo/qwt-interest
>