Making Modifier Key Events

April 11, 2003
by Alex Zavatone

Director is generally a very flexible environment. However, the handling of keyboard input leaves something to be desired. As Director currently exists keypresses on most keys generate keydown and keyup events. This is quite useful when the keys pressed are those that generate events but quite the PITA when the keys pressed do not. This ugly fact of like shows itself many times in cases that require key input. My particular need was to have a modifier key trigger a chain of events for the purpose of displaying command key graphics. Since no modifier keys (shift, command, control, alt and option) generate events when pressed, this quickly becomes something far from a piece of cake.

An entertaining thought would be to create an Xtra that would generate lingo events when these keys are pressed. My lack of knowledge of C programming proved to be a significant impediment in that regard. The concept here is to implement a solution at the lowest level possible. With the potential for an Xtra out of the picture, another approach needed to be developed. Director broadcasts events and intercepts them when a handler exists with the same name as the event. Everything starts and runs in Director because of these events and event interceptors. If Director could check for the desired keys at a desired interval, it could then make and broadcast its own brand new event and that event could be intercepted by a movie script.

An example of this concept could be accomplished with an idle script or a timeout as seen below

Movie script:

on Idle
  if the controlDown then
    ControlDown
  end if
  if the shiftDown then
    ShiftDown
  end if
end

on ControlDown
put "ControlDown"
-- do control stuff
end

on ShiftDown
put "ShiftDown"
-- do shift stuff
end

Think of this simple example not as calling a handler when the shift or control keys are pressed but instead broadcasting a movie level event that is intercepted by the movie level handler of the same name. By implementing the key checking at the lowest level possible, either at an idle or timeout interval, the overhead of this constant checking for key states can be kept as small as possible. Though encouraged not to use idle by some of the Director engineers years ago, I still find it useful as idle is supposed to be called only when there is time to do so. Whatever method we choose to perform the check for the keys, the problem here is that we need to send an event on a keypress and release, not all the time the key is held down. A way of solving this is to store the state of the key being pressed or released. To do this on a movie level requires either messy use of globals or another trick originally showed to my be Chris Leske over a year ago, that of movie script properties.

By declaring a property within a movie script, it can be referenced within the script it is defined in by explicitly referring to the script and the property. For example, if movie script 1 has a property called pControlDown, you would access it by reference to the script.property as seen below:

script (1).pControlDown = 0

Now, if a property is set up for each key we wish to store the state of when a key is pressed, we can check and see its current state value and determine if it is already down or up. This way, Director can then only broadcast an up or down event if the key was not in the same state previously.

With all that in mind, putting together a movie script that can broadcast modifier key events proves to be not too difficult. I've included a functional script that works perfectly on the Mac but may need some customization for Windows. It's meant to be in script 1 so if you plan on putting it elsewhere, you should replace the script reference with the number or name of the movie script all the code is in. I'll leave those changes as an exercise for the reader. Enjoy your new key events.

This script is available for download as a Director 8.5 movie in ZIP or SIT formats.

Movie Script: 1, Modifier Key Events

property pCommandDown
property pOptionDown
property pControlDown
property pShiftDown

on idle
  if the commandDown then
    CommandDown
  else
    CommandNotDown
  end if
  if the optionDown then
    OptionDown
  else
    OptionNotDown
  end if
  if the controlDown then
    ControlDown
  else
    ControlNotDown
  end if
  if the shiftDown then
    ShiftDown
  else
    ShiftNotDown
  end if
end

on ControlDown
  if script(1).pControlDown = 0 then
    script(1).pControlDown = 1
    -- here you can do stuff
    put "ControlDown"
  end if
end

on ControlNotDown
  if script(1).pControlDown = 1 then
    script(1).pControlDown = 0
    -- here you can do stuff
    put "ControlUp"
  end if
end

on CommandDown
  if script(1).pCommandDown = 0 then
    script(1).pCommandDown = 1
    -- here you can do stuff
    put "CommandDown"
  end if
end

on CommandNotDown
  if script(1).pCommandDown = 1 then
    script(1).pCommandDown = 0
    -- here you can do stuff
    put "CommandUp"
  end if
end

on OptionDown
  if script(1).pOptionDown = 0 then
    script(1).pOptionDown = 1
    -- here you can do stuff
    put "OptionDown"
  end if
end

on OptionNotDown
  if script(1).pOptionDown = 1 then
    script(1).pOptionDown = 0
    -- here you can do stuff
    put "OptionUp"
  end if
end

on ShiftDown
  if script(1).pShiftDown = 0 then
    script(1).pShiftDown = 1
    -- here you can do stuff
    put "ShiftDown"
  end if
end

on ShiftNotDown
  if script(1).pShiftDown = 1 then
    script(1).pShiftDown = 0
    -- here you can do stuff
    put "ShiftUp"
  end if
end

All colorized Lingo code samples have been processed by Dave Mennenoh's brilliant HTMLingo Xtra, available from his site at http://www.crackconspiracy.com/~davem/

A Director user since 1987, Alex (Zav) Zavatone has worked on the engineering teams for both Director and Shockwave, 4, 5, 6 and 7. Recent investigations find him developing foundation classes for Director with asynchronous process management and other life threatening activities. In its early days, he had something to do with this Internet thing known as "DOUG". A noted ne'erdowell, slacker and laggard, Mr. Zavatone is nonetheless is trusted by children, small animals and the elderly. In his spare time, Mr. Zavatone rehabilitates lame desert trout.