LocatorPane problem
- To: mathgroup at smc.vnet.net
- Subject: [mg78902] LocatorPane problem
- From: "Mariusz Jankowski" <mjankowski at usm.maine.edu>
- Date: Thu, 12 Jul 2007 05:21:34 -0400 (EDT)
- Organization: University of Southern Maine
I just came across the following problem with LocatorPane. This may crash
the kernel so save your work prior to reproducing this result.
Start the LocatorPane as in any of the examples in the Doc Center. For
example,
DynamicModule[{}, pts = {{0., 0.}};
LocatorPane[Dynamic[pts], Graphics[{Red, Disk[]}], LocatorAutoCreate ->
All]]
Delete the single Locator using Alt-Click.
Then Click to add one or more Locators. If possible, return the value of
pts. Here is my result - note the first element of the list.
In[11]:= pts
Out[11]= {{-6.27756*10^288, 1.14627*10^-286}, {0.246,
0.44}, {0.344, -0.065}, {-0.096, -0.21}}
The first time you click there will be no visible Locator symbol. However,
the list of click events/locations will be updated but with an incorrect
value (as above). Furthermore, dynamic monitoring of the value of pts during
interactive adding/deleting of Locators will kill the kernel at the first
click inside and empty pane.
I guess there is a problem with zero Locators in LocatorPane. Is this a bug
(I think so!), or are we supposed to use the two-argument form of Dynamic to
catch this condition? For example
DynamicModule[{}, pts = {{0., 0.}};
LocatorPane[Dynamic[pts, If[# == {}, do something, do something else]&],
Graphics[{Red, Disk[]}], LocatorAutoCreate -> All]]
Thanks for comments/suggestions, Mariusz