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Re: Exceed and IDL

David Fanning wrote:
> Several obtuse reasons for setting RETAIN=0 in a draw widget
> come immediately to mind:
> 
>    (1) You are using object graphics in the window, in which
>        case RETAIN should *always* be set to 0.
> 
>    (2) You know how screwy colors can be and you wish to
>        protect the colors associated with this application
>        by "restoring" your colors every time the widget is
>        exposed.

David points out some good reasons why an IDL programmer should not
assume a particular value for RETAIN. Here's a few other values/settings
that I've learned not to take for granted when an application runs (i.e.
I don't assume any particular value).

(1) DEVICE keywords:
RETAIN
DECOMPOSED
SET_CHARACTER_SIZE

(2) System variables:
!ORDER (order for displaying images)
!D.TABLE_SIZE (size of the color table)
!D.N_COLORS (number of colors available)
!D.NAME (name of the current display device)
!D.WINDOW (index of the current graphics window)

(3) Widget appearance:
WIDGET_CONTROL keyword DEFAULT_FONT

Anyone else care to add to the list?

Cheers,
Liam.

-- 
Liam E. Gumley
Space Science and Engineering Center, UW-Madison
http://cimss.ssec.wisc.edu/~gumley