Re: A community Windows binding

[Stephen Leake <stephen_leake@acm.org>]

Jeffrey Carter <spam@spam.com> writes:

> Callbacks and dispatching are essentially the same thing in a
> windowing system. You have to write little pieces of code that can be
> invoked in any order at any time outside your control. You have to use
> global variables extensively for these little pieces of code to
> communicate. The code is difficult to read because you have to
> understand all these little pieces to understand any part of the
> software.

In Windex, GWindows, CLAW, and GtkAda, each "little piece of code" has
as a parameter the user window type. That type stores all the
information needed; no global variables are necessary.

I can (with a lot of effort to suppress my normal style :) write
messy, hard to read code in Windex, using global variables. But it's
certainly not required.

> With an event queue approach, one writes standard imperative
> software using your standard imperative language (Ada's about the
> only one). The code is well structured and easy to read and
> understand.

MS Windows has an event queue. The core program in Windex, CLAW, and
GWindows reads events from the event queue as they become available,
and calls the appropriate handler, via dispatching. or optionally via
a registered callback in GWindows.

The handler may make GUI calls that put other events on the event
queue (like "invalidate this rectangle" or "hide this widget"). Some
GUI calls call the main event handler directly, rather than going thru
the queue.

GtkAda is similar, but fewer things go thru the queue, and all handlers
are registered callbacks.

What is it you are talking about that is different?

I guess I should go look at the JEWL code.

-- 
-- Stephe