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Re: locator snap

  • To: mathgroup at smc.vnet.net
  • Subject: [mg88277] Re: locator snap
  • From: Szabolcs Horvát <szhorvat at gmail.com>
  • Date: Wed, 30 Apr 2008 04:25:53 -0400 (EDT)
  • Organization: University of Bergen
  • References: <fv6ukg$rmt$1@smc.vnet.net> <4817399A.1030901@gmail.com>

Szabolcs Horvát wrote:
> Maarten van der Burgt wrote:
>> Dear all,
>>
>> In the example below the locator can be moved to any position in the 
>> graphic.
>> Can the locator be made to snap to multiples of say 0.1?
>>
>>  Manipulate[Column@{Graphics[{}, Axes -> True], p}, {{p, {0, 0}}, 
>> Locator}]
>>
> 
> Hi Maarten,
> 
> I am not aware of any way to do this directly with Manipulate. (Of 
> course this does not mean that there doesn't exist a way!)
> 
> Here is an example of doing it directly with Dynamic:
> 
> Graphics[
>  Locator[Dynamic[{x, y}, ({x, y} = Round[#, 0.1]) &]],
>  PlotRange -> 1, Frame -> True,
>  GridLines -> {#, #} & @
>   Table[{x, If[Mod[x, 1/2] == 0, Black, Gray]}, {x, -1, 1, 1/10}]
>  ]
> 

Sorry, I forgot to mention that x and y must be initialized before this 
will work:

{x, y} = {0, 0}

Also, the x in the Table is an unfortunate choice for a local variable 
name---it has nothing to do with the x in the Dynamic.


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