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MathGroup Archive 2007

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Re: Re: Locator Appearance mystery in LocatorPane

  • To: mathgroup at smc.vnet.net
  • Subject: [mg80037] Re: [mg80009] Re: [mg79984] Locator Appearance mystery in LocatorPane
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Sat, 11 Aug 2007 02:07:01 -0400 (EDT)
  • Organization: Mathematics & Statistics, Univ. of Mass./Amherst
  • References: <200708101038.GAA14017@smc.vnet.net>
  • Reply-to: murray at math.umass.edu

I'm still not sure I completely understand....

OK, as I can see, the locator is a large, framed, red rectangle when I use

   dot=Graphics[{PointSize[Medium],Point[{0,0}]},Background->Red,
                 Frame->True]

but why, given the option LocatorAutoCreate->All, don't I then see a 
bunch of large, framed, red rectangles when I click to create new 
points?  Is it just that the new "points" are really there but I cannot 
see them, that I can only see the one "point" that's on top because I 
created it last?


John Fultz wrote:
> On Fri, 10 Aug 2007 01:45:30 -0400 (EDT), Murray Eisenberg wrote:
>> Here's a LocatorPane inside a DynamicModule with a Locator initialized
>>
>> at the origin and where additional Locator points will be created at
>> mouse clicks:
>>
>> dot=Automatic;
>>
>> DynamicModule[{pts = {{0, 0}}},
>> LocatorPane[Dynamic[pts],
>> Graphics[Point /@ pts],
>> Appearance -> dot,
>> LocatorAutoCreate -> All]
>> ]
>>
>> This works as expected. (The setting Automatic for Appearance is the
>> default.)
>>
>> Now change the definition of dot to:
>>
>> dot=Graphics[Disk[],ImageSize->5]
>>
>> Still OK.  But, finally, change the defintion of dot to:
>>
>> Graphics[{PointSize[Medium],Point[{0,0}]}]
>>
>> Now it does NOT work as expected: Although the initialized points do
>> appear correctly, and a new dot appears at the first click in the
>> output, upon each additional click a new dot does not appear but,
>> instead, that one new dot moves to the location of the click.
>>
>> Diagnosis?  Cure?
> 
> This is correct behavior.  If you change dot to be...
> 
> dot = Graphics[{PointSize[Medium], Point[{0, 0}]}, Background -> Red, 
>   Frame -> True]
> 
> ...and play around with the result, the reason for the behavior should start to 
> be come obvious.  The default size of a Graphics[] object is the size of the
> graphic.  And the entire graphics object represents the Locator, so all you're 
> doing is moving the existing Locator (as you should correctly do when clicking 
> directly on a Locator), rather than creating a new one.  The only reason the
> Disk[] example worked as you expected is because you set the ImageSize to be so 
> small, which affected the size of not just the disk, but the Locator itself.
> 
> Sincerely,
>  
> John Fultz
> jfultz at wolfram.com
> User Interface Group
> Wolfram Research, Inc.
> 
> 
> 

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305


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