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Re: Another Long Day Compliments of Object Graphics

"David Fanning" <davidf@dfanning.com> wrote in message
> Mark Hadfield (m.hadfield@niwa.cri.nz) writes:
> > Plain IDLgrImages are "funny" in other ways. In particular, where images
> > involved, visibility is controlled by drawing order, not vertical
> > So moving your colour bar into some other sort of container is a good
> Maybe I'm just plum wore out, but I don't understand this,
> Mark. Could you elaborate?

When I wrote "So moving your colour bar into some other sort of container is
a good idea" I should have written "So representing the colour ramp in your
your colour bar with some sort of atom other than a stand-alone IDLgrImage
is a good idea". I was just agreeing with you--unusual, I admit.

The bit about IDLgrImages being "funny" referred to the fact that they are
two-dimensional objects in an otherwise 3-dimensional object graphics world.
This means (as you pointed out) you can't rotate them satisfactorily. It
also means that you can't control visibility by putting images above  or
below other atoms in the Z direction. If you put an image then another atom
into a model, the other atom is visible over the image irrespective of its
vertical position. If you reverse the order in which they are put into the
model, the other atom is not visible over the image, again irrespective of
its vertical position. At least that's what my experience shows.

Of course the general guideline that you should control visibility/overlap
of graphics atoms (other than images) by vertical position and not drawing
order is one of those secrets the IDL documentation doesn't want to tell us.

Mark Hadfield
m.hadfield@niwa.cri.nz  http://katipo.niwa.cri.nz/~hadfield/
National Institute for Water and Atmospheric Research
PO Box 14-901, Wellington, New Zealand