Simple GUI application attempted.

From: flesh_eating_dragon (dragon_at_netyp.com.au)
Date: 07/23/04 

Date: 23 Jul 2004 05:13:05 -0700

Some assistance in the development of a simple GUI application would
be appreciated.

Not long ago I completed a computer science degree, and right now I
want to get a bit more experience and confidence by trying to write
applications that are just a bit beyond what I had to write at
university. However, in the early stages of designing the application
that I have in mind, I have hit a brick wall. I can't write it the way
that I thought at first would work, because of the ColorModel classes
having no 'set' methods, so I'd like to know what _will_ work.

Please imagine the following scenario (this is not a description of
the application, but it is a simpler illustration of the same
problem). Suppose you are writing a graphical application that
simulates a digit on a traditional LCD display, as for example on
a handheld calculator. This should be achievable using a Raster that
encodes something akin to the following:

  011110
  200003
  200003
  044440
  500006
  500006
  077770

and a changeable ColorModel, in which 0 always represents the
BACKGROUND colour and the other indexes 1 to 7 represent colours that
we will call ON and OFF. For example, if the digit to be displayed is
"4", then indexes 2, 3, 4 and 6 will be set to represent colour ON
whilst indexes 1, 5 and 7 will be set to represent colour OFF.
Similarly, if the digit to be displayed is "3", then indexes 1, 3, 4,
5 and 7 will represent ON and indexes 2 and 6 will represent OFF.

It would be nice if the ColorModel classes had 'set' methods, because
then you could make the relevant class (let's call it
DigitDisplayImage) a subclass of Image, and the rest would be elegant
and easy. But it doesn't, although I feel there _should_ be a similar
solution. Then you could write setIndex(int, Color) methods in the
DigitDisplayImage class, after which the following code example would
work to display the digit "4".

   digitDisplay.setIndex(1, OFF);
   digitDisplay.setIndex(2, ON);
   digitDisplay.setIndex(3, ON);
   digitDisplay.setIndex(4, ON);
   digitDisplay.setIndex(5, OFF);
   digitDisplay.setIndex(6, ON);
   digitDisplay.setIndex(7, OFF);

This would be lovely.

In the absence of ColorModel classes with 'set' methods, how, in
practise, should I go about achieving a similar functionality? (In the
real application, the corresponding object needs a lot more than eight
index values and will be called upon to display far more than just
digits between 0 and 9, but I think it is better to discuss the
problem with reference to this simplified example.)

Thanks,

Adrian.

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