Re: [Vxl-maintainers] Recommended event handling for vgui

[<kar...@ya...>]

As things stand, if you are looking for a SHIFT+b key-press event then you
may:
 1) Look for modifier=vgui_SHIFT && key='b'
 2) Look for ascii_char = 'B'

Both vgui_event and vgui_event_condition contain modifier, key and
ascii_char so both have the same problems regarding how modifiers effect a
key-press.  I don't use vgui_event_condition because I don't see much
advantage in using it (except perhaps that the constructors do some error
checking for you).  We are left with (at least) four ways of detecting a
key-press event which I guess may appear confusing but I am happy with it.
 For comparison here are the four ways you could detect a SHIFT+b event in
your handle function:

Using straight vgui_events:
1)   if (event.modifier == vgui_SHIFT && event.key == 'b')
       
2)   if (event.ascii_char == 'B')

Using vgui_event_condition:
1)   vgui_event_condition my_ec(vgui_key('b'), vgui_SHIFT);
     if (my_ec(event))

2)   vgui_event_condition my_ec(vgui_key('B');
     if (my_ec(event))

Inside the key_press convenience method there is only one way to detect
this event (which is certainly less confusing though perhaps debatable
whether it is "convenient"):

  if (key == 'b' && modifier == vgui_SHIFT)

Regarding portability.  As things stand - everything works exactly as it
should on Windows using MFC (Awf and I fixed it a couple of weeks ago) so
any one of these four methods is fine.  For GTK, all four cases would work
for this example because GTK works for letter presses ('a'-'z' and 'A' to
'Z) but symbols are not correct - I believe this could be fixed.   For Qt,
I had a look and key-press events are not implemented at all for Qt so you
will never get a key-press using Qt - I see no reason why it could not be
implemented correctly.

Personally I see no advantage in recommending vgui_event_condition's or do
other people love them?
Karen McGaul
VGG, Oxford University

 --- Amitha Perera <pe...@cs...> wrote: > Hi all
> 
> What is the recommended way of handling events in vgui tableaus for
> maximum portability?
> 
> In particular, my concern is with key events. It appears that we
> cannot simply check for a 'B' key event portably, because the event
> may be a 'b'+shift. I know about the ascii_char member, but is it
> portable?
> 
> It seems that vgui_event_condition may be the best way to handle
> things. However, this implies that most events should be handled in
> the handle() method, and not in the key_press convenience method. In
> fact, it seems that the key_press method is not so convenient any
> more.
> 
> Am I missing something? If not, should the vgui_event_condition
> approach be documented as a "recommendation"? With the understanding,
> of course, that you are free to do what ever you like.
> 
> Thanks,
> Amitha.
> 
> 
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