Selecting a rectangular area of Canvas of QwtPlot

I am facing problem in selecting the rectangular area on canvas of qwtplot using different color.

I have to select so that wherever i click and move the mouse the selection will move on x axis and whole y axis should be selected.ie the length of rectangle will be whole y axis nad width will mouse clicked and moved.

Please suggest me how should I implement through qwt.
I am new to qwt. :( If possible please give the sample code.

Thanks in advance.:)

QwtPlotPicker is intended to support selections on the plot canvas.

Uwe