overlay a variable size box/rectangle over a incoming signal to indicate to user the area of signal being examined

[Canofsteam]

im not sure if this is possible but .....

in a nut shell i would like to overlay a variable size box/rectangle over a incoming signal (XY Graph)

to indicate to the user the area of signal being examined

my code will take in the user input (the x axis values range). 

then draw a line up as far as the y value of the signal.

or a box or rectangle to show the user the area in question.

a shaded box would be cool but at this point im not that picky.

Any tips/pointers/ advice?

John

attached a quick sketch of what im trying to do.

[TCPlomp]

Create a picture indicator witha transparent background. Draw a yellow rectangle on it in the size you need and move indicator to the position you need.

Ton

[Canofsteam]

ill give it a go. thanks