OpenEuphoria

2. Re: Stupid callback question

• Posted by "Cuny, David" <David.Cuny at DSS.CA.GOV> Apr 05, 1999
• 483 views

Paul Martin wrote:

> The question is, if I'm not using all of the [GLUT] events,
> will I have to set the ones I'm not using to NULL.

Assuming that I'm understanding the question, you have set up something like
this:

        if iMsg = EVENT1 then
                ...
                call_proc( HANDLE_EVENT1, {...} )

        elsif iMsg = EVENT2 then
                ...
                call_proc( HANDLE_EVENT2, {...} )

        elsif iMsg = EVENT3 then
                ...
                call_proc( HANDLE_EVENT3, {...} )
        end if

And since your application never uses EVENT3 (for example), how can you make
sure that it doesn't get triggered?

Remember that, unlike most of the Euphoria functions, a routine id value of
zero/NULL is *valid*. I sort of wish that call_proc and routine_id worked
differently than they currently do - especially for cases like this. It
would be *nice* if 0 meant "do nothing" and -1 meant "error, undefined"...
but that's not how it (currently) works. 

You probably can't initialize your variables to a "do nothing" routine,
because each no op procedure will have to have the correct number of
arguments associated with it. You might consider initializing all your
variables to -1 and redefining call_proc and call_func to something like
this:

        global procedure callProc( integer routineId, sequence args )
                if routineId > -1 then
                        call_proc( routineId, args )
                end if
        end procedure

        global procedure callFunc( integer routineId, sequence args )
                if routineId > -1 then
                        return call_func( routineId, args )
                else
                        return 0
                end if
        end procedure

Of course, if you are ever expecting something other than a number back from
callFunc, you are in trouble with callFunc, so I typically bite the bullet
and just code it manually:

        if HANDLE_EVENT1 > -1 then
                call_proc( HANDLE_EVENT1, args )
        end if

Hope this helps.

-- David Cuny