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MGHGRAXIS__DEFINE

MGHGRAXIS__DEFINE

Class Name


  MGHgrAxis

Purpose


  An MGHgrAxis is an axis specialised for use by objects of the
  MGHgrGraph class and its subclasses. The class is based on the
  IDLgrAxis, but with several differences:
    - The TITLE and TICKTEXT properties are strings. Behind the
      scenes, corresponding IDLgrText objects are created
      and modified as necessary.
    - The following properties are passed to the axis's title and
      tick-text objects: ENABLE_FORMATTING (default 1), FONT and
      RECOMPUTE_DIMENSIONS (default 2). These properties are applied
      to *both* objects. (This loses a lot of generality, but it also
      simplifies the interface & coding.)
    - A new property, NORM_RANGE, specifies the end points of the
      axis in normal coordinates. When the axis is changed in a way
      that affects its range in data coordinates, the
      coordinate conversion is changed to keep the normalised range
      constant. The [X,Y,Z]COORD_CONV properties are retained but
      are read-only.
    - It can participate in master-slave relationships (see below).
  MASTER-SLAVE RELATIONSHIPS
  An MGHgrAxis can participate in master-slave relationships with
  axes, atoms and symbols. When changes are made that affect the
  scaling and/or position of a master axis, it passes on those
  changes to its slaves.
  In relationships with atoms and symbols, an MGHgrAxis is always
  a master. For atoms it passes on changes in the relevant
  [X,Y,Z]COORD_CONV property. For symbols it adjusts the relevant
  component of SIZE so as to preserve the normalised size of the
  symbol. There are no restrictions on the class of the atoms or
  symbols, provided they support the required properties.
  The master-slave relationship between axes is intended to support
  situations where there are two more-or-less identical axes on a
  graph. Both parties in such a relationship must be instances of
  MGHgrAxis and there are various restrictions, e.g. a slave axis
  may not itself have slaves (of any sort) and a slave axis cannot
  have two masters. These rules are enforced to keep dependencies
  very simple (there being no good reason to allow complicated ones)
  and avoid circular dependencies and other subtle effects that
  depend on the order in which changes are passed on.
  Each MGHgrAxis has a property called MS_STATUS; it is an integer
  that can take three values: -1 (I am a slave), 1 (I am a master),
  0 (I am neither). The MS_STATUS property is used to enforce the
  above restrictions on the master-slave relationships. It can only
  be acessed via by the axis itself, or via the FriendGetProperty &
  FriendSetProperty methods. When these methods are called an object
  reference must be supplied and it must refer to an MGHgrAxis
  object. This provides a barrier (though a very weak one) to
  setting the property inappropriately.
  A slave axis cannot have more than one master but an atom or
  symbol can. Normally each atom or symbol will have 2 or 3 masters,
  one each for the X, Y and (maybe) Z directions. It would not make
  sense for an atom or symbol to have two masters with the same
  direction, but no attempt is made to test for this state (because
  doing so would require code in every atom & symbol class).

Background


  The central concept behind the MGHgrGraph class is that the axes
  in a graph define coordinate conversions, which are then adopted by
  atoms and symbols as they are added to the graph (or in the case of
  animations, fitted to the graph and added or removed during playback).
  The MGHgrAxis class takes this concept a step further in that
  axes keep references to the objects (slaves) that have been fitted
  to them and update their slaves if any of the axis's relevant
  properties is changed.

Properties


  In addition to the properties inherited from MGHgrAxis:
    ATOM_RANGE (Get)
      This keyword to GEtProperty retruns the envelope of the slave
      atoms' XRANGE, YRANGE or ZRANGE properties (depending on the
      axis direction. Note that this property may be undefined or
      unchanged on output from GetProperty, if the axis has no slave
      atoms, or if none of the slave atoms supports the required
      RANGE property.
###########################################################################
  Copyright (c) 2000-2012 NIWA:
  http://www.niwa.co.nz/
  Licensed under the MIT open source license:
  http://www.opensource.org/licenses/mit-license.php
###########################################################################

Modification History


  Mark Hadfield, 1999-05:
    Written.
  Mark Hadfield, 2000-08:
    Revisited and generally revised
  Mark Hadfield, 2001-07:
    Keyword inheritance updated for IDL 5.5.
  Mark Hadfield, 2004-07:
    The MGHgrAxis class incorporates master-slave functionality from the
    MGHgrMSaxis class, now obsolete.
  Mark Hadfield, 2006-03:
    Fixed a long-standing bug: initialisation fails when no font is specified.



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