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Re: Simulating a Mouseover event in EventHandler

  • To: mathgroup at
  • Subject: [mg91244] Re: Simulating a Mouseover event in EventHandler
  • From: David Bailey <dave at>
  • Date: Mon, 11 Aug 2008 06:06:39 -0400 (EDT)
  • References: <g7lvoh$fpq$>

chandler.seth at wrote:
> I would like to create an interface so that when the mouse moves
> within certain graphics primitives within a Graphics object various
> global variables are set that, among other things, alter both the
> object itself and, potentially, other directives or graphics
> primitives within the object. I would have thought that EventHandler
> would have an event such as "Mouseover" or "MouseIn" or "MouseOut"
> that handled this sort of thing. But, so far as I can see, it does
> not.
> Here is the best code I've been able to come up to address this idea.
> But it just looks really ugly and wrong. Anyone have ideas?
> (mouseisover = False; {Dynamic[mouseisover],
>   Graphics[{Dynamic[{If[mouseisover, Red, Green], Disk[{3, 3}, 1/2]}],
>      Dynamic@
>      If[mouseisover, {Black, Line[{{1, 1}, {2, 2}}]}, {Black,
>        Circle[{1, 2}, 1/2]}],
>     Dynamic@EventHandler[{If[
>         MousePosition["EventHandlerScaled", False] /. {x_, y_} :>
>           True, (mouseisover = True; Yellow), (mouseisover = False;
>          Blue)], Disk[{0, 0}, 1]}, {(* no events are defined,
>        which makes me think that the event handler construct is \
> unnecessary *)}]}, Frame -> True]})
> P.S. The Mouseover command does not appear to accomplish what I need
> because, even with compound expressions as the arguments and Dynamic,
> I cannot get it to alter global variables. But maybe I am missing
> something.
Here is a solution using MouseAnnotation. Note that although the effect 
of this example could be achieved using MouseOver, the function foo can 
do anything you want.

foo[] := If[MouseAnnotation[] === Null,
    Graphics[{RGBColor[0, 0, 0], Disk[]}],
    Graphics[{RGBColor[1, 0, 0], Disk[]}]];

Annotation[Dynamic[foo[]], "An annotation", "Mouse"]

 From my experiments, it would seem that the function foo is called more 
frequently than I would have expected - so bear this in mind.

David Bailey

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