How to draw rectangle on a figure, based on mouse location?

Hello, I'd like to "live-draw" a rectangle on my figure, based on mouse location.

I'm using the following:

set (gcf, 'WindowButtonMotionFcn', @mg_BPP_mouseMove);

function mg_BPP_mouseMove(object,eventdata)
    windowSize = 64;

    C = get (gca, 'CurrentPoint');

    topLeftCornerX = round(C(1,1)) - windowSize/2;
    topLeftCornerY = round(C(1,2)) - windowSize/2;
    width = windowSize;
    height = windowSize;

    imrect(gca, [topLeftCornerX, topLeftCornerY, width, height]);
end

Two questions:

1. How can I make the windowSize be an input variable of mg_BPP_mouseMove? I don't want explicitly define it within the function itself.

2. At the moment it draws lots of rectangles (like a "snake") as my mouse moves across the figure. I'd like to display only the last one. I mean, I would like to have one rectangle that "flows" with my mouse cursor.

Answer 1

[Guillaume]

For 1, create an anonymous function that binds the window size to BPP_mouseMove (with an added input argument).

For 2, keep track of the previously drawn rectangle and delete it.

windowsize = 40;
set(gcf, 'WindowButtonMotionFcn', @(source, eventarg) mg_BPP_mouseMove(source, eventarg, windowsize));

 function mg_BPP_mouseMove(object, eventdata, windowSize)
      persistent lastrect;      
      C = get (gca, 'CurrentPoint');
      topLeftCornerX = round(C(1,1)) - windowSize/2;
      topLeftCornerY = round(C(1,2)) - windowSize/2;
      width = windowSize;
      height = windowSize;
      if ~isempty(lastrect) && lastrect.isvalid
         delete(lastrect);
      end
      lastrect = imrect(gca, [topLeftCornerX, topLeftCornerY, width, height]);
  end

[Mark Golberg]

THANKS A LOT Guillaume!!!

Answer 2

[Walter Roberson]

http://www.mathworks.com/help/images/ref/getrect.html

[Mark Golberg]

Thank you Walter.

A) could you help me with my first question also please?

B) getrect is not my intention. Please note, I'm using WindowButtonMotionFcn in order for the rectangle to appear without me pressing the mouse.