| Propagating properties [message #13161] |
Fri, 16 October 1998 00:00 |
Struan Gray
Messages: 178
Registered: December 1995
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Senior Member |
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I've decided to set myself a programming excercise in order to
really get to grips with objects - as opposed to reading the manual
and fooling myself that I understand it. I am concentrating on a
program to draw crystal and surface atomic structures, since the
structure definitions are nicely hierarchical and can easily be
objectified, and because I need good 3D plotting so I am forced to use
object graphics.
I've been playing with generating arrays of spheres using multiple
instances of the example 'orb' object. This works nicely and simply
but I've hit a conundrum. I would like to create an ur-orb which
represents an element, say Si, with properties such as size and colour
which are adopted by all the instances of Si in the crystal. A
problem crops up when after creating the crystal I decide that all the
Si atoms should be green rather than blue, or that they should be a
different size. I would like to be able to just edit the ur-orb and
have the changes propagate automatically, without having to re-create
the whole crystal from scratch (which takes some time on my computer).
I can think of various ways to deal with the problem. The the two
most promising are for the ur-orb to maintain a list of dependent
objects (which seems ugly and slightly defeats the point of object
programming), or I can subclass 'orb' to create an 'atom' class that
checks with a specific ur-orb parent every time it draws itself (which
has a performance hit, and suffers from the lack of a 'copy object' or
'copy properties' command discussed here previously). Does anyone
have a better idea?
Also, if anyone knows of a library of other 3D graphics primitives
(cylinders, cones etc) along the lines of 'orb' I would love to know
about it.
Struan
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