crosshair(n)                      Crosshairs                      crosshair(n)



______________________________________________________________________________

NAME
       crosshair - Crosshairs for Tk canvas

SYNOPSIS
       package require Tcl  ?8.4?

       package require Tk  ?8.4?

       package require crosshair  ?1.1?

       crosshair::crosshair w ?arg...?

       crosshair::off w

       crosshair::configure w ?arg...?

       crosshair::track on w cmdprefix

       crosshair::track off w

       crosshair::bbox_add w bbox

       crosshair::bbox_remove token

______________________________________________________________________________

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

API
       The following commands are exported to the public:

       crosshair::crosshair w ?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::off w
              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::configure w ?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::track on w cmdprefix
              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::track off w
              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_add w bbox
              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_remove token
              This command removes the bounding box specified by the token (a
              result of crosshair::bbox_add) from the crosshairs for its
              canvas widget.

BUGS, IDEAS, FEEDBACK
       This document, and the package it describes, will undoubtedly contain
       bugs and other problems.  Please report such in the category tklib ::
       crosshair of the Tcllib SF Trackers
       [http://sourceforge.net/tracker/?group_id=12883].  Please also report
       any ideas for enhancements you may have for either package and/or
       documentation.

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

KEYWORDS
       canvas, cross-hairs, location, tracking, viewport

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




tklib                                 1.1                         crosshair(n)
