NAME

       canvas::track::lines - Manage a group of rubber band lines

SYNOPSIS

       package require Tcl  8.5

       package require Tk  8.5

       package require canvas::tag  ?0.1?

       ::canvas::track lines objectName canvas

       objectName destroy

       objectName start current p...

       objectName move current

       objectName done

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DESCRIPTION

       This  package  provides  a  utility  class  managing  the drawing of set of semi-crosshair
       (rubberband) lines.

CLASS API

       ::canvas::track lines objectName canvas
              This, the class command, creates and configures a  new  instance  of  the  tracker,
              named objectName. The instance will be connected to the specified canvas widget.

              The result of the command is the fully qualified name of the instance command.

INSTANCE API

       Instances of this class provide the following API:

       objectName destroy
              This method destroys the instance and releases all its internal resources.

              This  operation  does destroy the items representing the tracked lines. It does not
              destroy the attached canvas.

              The result of the method is an empty string.

       objectName start current p...
              This method starts the tracking of a set of lines, one  line  per  point  p,  which
              specifies  the destination end-point of each line. All lines will have current as a
              common end-point.

              Note that a previously tracked set of lines is removed.

              The result of the method is an empty string.

              Each point is  specified  through  a  2-element  list  containing  its  x-  and  y-
              coordinates, in this order.

       objectName move current
              This method updates the shared end-point of all rubberbands and redraws them.

              The result of the method is an empty string.

              The  point  is  specified  through  a  2-element  list  containing  its  x-  and y-
              coordinates, in this order.

       objectName done
              This method ends the tracking of the current set of lines and removes them from the
              canvas.

KEYWORDS

       canvas, crosshair, rubberband, tracking