crosshair - Crosshairs for Tk canvas

       The following commands are exported to the public:

       crosshair::crosshairw ?arg...?
              This  command  activates  the display of a pair of cross-hairs for the canvas widget w. The cross-
              hairs track the pointing device. The result of the command is the empty string.

              All arguments after the widget w are treated as options as  for  a  canvas  line  item  in  w.  Of
              particular interest are -fill and -dash.

       crosshair::offw
              This  command removes the cross-hairs from the canvas widget w.  Nothing is done if the widget had
              no cross-hairs. The result of the command is the empty string.

       crosshair::configurew ?arg...?
              This command changes the appearance of the cross-hairs in the canvas widget w. It is an  error  to
              call it for a canvas which has no cross-hairs.

              All  arguments  after  the  widget  w  are  treated  as options as for a canvas line item in w. Of
              particular interest are -fill and -dash.

              The result of the command are the current configuration settings.

       crosshair::trackonwcmdprefix
              This command activates reporting of the location of the cross-hairs in the canvas widget w. It  is
              an  error  to use this command for a canvas which has no cross-hairs. The result of the command is
              the empty string.

              After the invokation of this command  the  specified  command  prefix  cmdprefix  will  be  called
              whenever the mouse moves within the canvas, with 7 arguments. These are, in order:

              [1]    The widget w

              [2]    The x-location of the cross-hairs, in pixels.

              [3]    The y-location of the cross-hairs, in pixels.

              [4]    The x-location of the top-left corner of the viewport, in pixels.

              [5]    The y-location of the top-left corner of the viewport, in pixels.

              [6]    The x-location of the bottom-right corner of the viewport, in pixels.

              [7]    The y-location of the bottom-right corner of the viewport, in pixels.

              A  previously  existing  callback  for w will be disabled. I.e. per canvas widget with cross-hairs
              only one callback reporting their location is possible.

       crosshair::trackoffw
              This command disables the reporting of the location of the cross-hairs in the canvas widget w.  It
              is  an  error to use this command for a canvas which has no cross-hairs. The result of the command
              is the empty string.

       crosshair::bbox_addwbbox
              This command adds a bounding box to the crosshairs for canvas w.   The  crosshairs  will  only  be
              active within that area.

              The  result  of  the  command  is  a  token  with which the bounding box can be removed again, see
              crosshair::bbox_remove below.

              The bounding box bbox is specified thorugh a list of 4 values, the  lower  left  and  upper  right
              corners of the box. The order of values in the list is:

              llx lly urx ury

       Note that this command can be used multiple times, each call adding one more bounding box. In such a case
       the visible area is the union of all the specified bounding boxes.

       crosshair::bbox_removetoken
              This  command  removes  the  bounding box specified by the token (a result of crosshair::bbox_add)
              from the crosshairs for its canvas widget.

       This  document,  and  the package it describes, will undoubtedly contain bugs and other problems.  Please
       report such in the  category  crosshair  of  the  TklibTrackers  [http://core.tcl.tk/tklib/reportlist].
       Please also report any ideas for enhancements you may have for either package and/or documentation.

       Copyright (c) 2003 Kevin Kenny
       Copyright (c) 2008 (docs) Andreas Kupries <andreas_kupries@users.sourceforge.net>
       Copyright (c) 2013 Frank Gover, Andreas Kupries

tklib                                                 1.2.1                                       crosshair(3tk)

       The crosshair package provides commands to (de)activate and track crosshairs on canvas widgets.

       canvas, cross-hairs, location, tracking, viewport

       crosshair - Crosshairs for Tk canvas

       package require Tcl?8.4?

       package require Tk?8.4?

       package require crosshair?1.2.1?crosshair::crosshairw ?arg...?

       crosshair::offwcrosshair::configurew ?arg...?

       crosshair::trackonwcmdprefixcrosshair::trackoffwcrosshair::bbox_addwbboxcrosshair::bbox_removetoken

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