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Time based progress bar

September 26, 1999
by Pat McClellan

Dear Multimedia Handyman,

I think the term for what I am trying to do is called a countdown bar or an energy bar. It will be a graphic which will go down in size as time elapses. Can you help?

Mike Oscar

Dear Mike,

What you're describing sounds like a progress bar -- similar to what you see when you're downloading a file or installing a program. The difference is that you want the progress tied to time (rather than bytes downloaded) and you want the bar to shrink over time, rather than grow. You don't mention whether the bar will be horizontal or vertical, so I'll just create something that works either way.

Let's think about what we want the author (you) to be able to specify when you drop it on a sprite. Obviously, you'll want to enter the number of seconds. You want to say whether the bar is oriented horizontally or vertically. And, although in this instance you want it to shrink, let's add an option so that the bar can either increase or decrease in size. Here's what it should look like.

And here's what the final result could look like.

A sample movie is available for download in Mac or PC format

So how do we make it work? Everything you're seeing in the demo above is handled by one behavior, which I'm calling the "progressBar timer". Here's the concept in a nutshell: as soon as the sprite comes into existence, it starts a timer. It also checks its own width (or height, if the bar is vertical). Then, at each frame after that (until the specified amount of time as elapsed) it calculates how much time has passed as a percentage of the total time specified. This percentage is then applied to the original width of the sprite to yeild a graphic representation of the time.

In our beginSprite handler, we'll need to initialize values for several properties of the sprite: width, height, and sprite number. We'll also convert the seconds to ticks (60ths of a second) so that our calculations will be more precise. We'll then record the starting time (in ticks). Finally, we need to add this behavior instance to the actorList. What the heck does that mean?

The actorList is a feature used mostly by people who are doing higher level object oriented programming. But it's very easy to use, once you grasp the concept. Here's how it works and why you'd want to use it.

In our example, we want the behavior to update its size every frame. So we could just use an enterFrame, exitFrame or prepareFrame handler for that. Right? Well... almost. In actuality, we want the behavior to update its size every frame... until the full time has elapsed. After the time has elapsed, there's no need to waste the processor's time by going through that handler anymore. Alot of times, I use a "flag" property to act as a switch, but that's a little inefficient because the behavior still has to check the status of the flag every frame -- even if it is "off".

Instead, we can use "the actorList". Any object which is contained in the actorList automatically gets a prompt from Director every frame. The prompt is called "stepFrame". It's as if on every frame, Director looks in the actorList. If it sees "Bob" in the actorlist, it says "Hey Bob, execute that stepFrame handler!".

So, what we'll do is add this behavior to the list in the beginSprite handler. Then, after the time has elapsed, the behavior will delete itself from the actorList and it won't get the prompt to stepFrame anymore. The main guts of our behavior will be executed in the stepFrame handler.

property pSecs, pTotalTicks, pWidth, pHeight, pSprite
property pStartTicks, pDirection, pOrientation
on beginSprite me
  pSprite = sprite(me.spriteNum)
  pWidth = pSprite.width
  pHeight = pSprite.height
  pTotalTicks = pSecs * 60
  pStartTicks = the timer
  add the actorList, me
  
end beginSprite
on stepFrame me
  if the timer > pStartTicks + pTotalTicks then
  
    if pDirection = #increase then
      pSprite.width = pWidth
      pSprite.height = pHeight
    else
      pSprite.width = 0
      pSprite.height = 0
    end if
        
    deleteOne the actorList, me
    -- do whatever else you want
    beep
        
  else 
  
    timeElapsed = the timer - pStartTicks
    percentTime = (timeElapsed * 1.0000/pTotalTicks)
        
    if pDirection = #increase then
      if pOrientation = #horizontal then
        pSprite.width = percentTime * pWidth
      else
        pSprite.height = percentTime * pHeight
      end if
    else
      if pOrientation = #horizontal then
        pSprite.width = pWidth - (percentTime * pWidth)
      else
        pSprite.height = pHeight - (percentTime * pHeight)
      end if
          
    end if
        
  end if
  
end stepFrame
on endSprite me
  deleteOne the actorList, me
end endSprite
on getPropertyDescriptionList me
  set pdlist to [:]
  myWidth = sprite(the currentSpriteNum).member.width
  myHeight = sprite(the currentSpriteNum).member.height
  
  if myHeight > myWidth then
    defOrientation = #vertical
  else
    defOrientation = #horizontal
  end if
  
  addprop pdlist, #pSecs, [#comment:"How many seconds?", ¬
    #format:#integer, #default:30]
  addprop pdlist, #pDirection, [#comment:"Count which way?", ¬
    #format:#symbol, #default:#increase, #range:[#increase,#decrease]]
  addprop pdlist, #pOrientation, [#comment:"Orientation?", #format:¬
    #symbol, #default:defOrientation, #range:[#horizontal,#vertical]]
  
  return pdlist
  
end getPropertyDescriptionList

The stepFrame handler isn't very complicated. It looks about twice as long as necessary because I've included the option for the bar to be oriented vertically. So, for every command to change the size of the bar, there's an if statement that checks the pOrientation property and then issues the appropriate command to adjust either the width or height.

The first thing the stepFrame handler does is check to see if the full time has elapsed. If so, it checks to see if the bar was counting up or down and then sets the sprite to its full width/height, or to 0. And then it does something very important: it removes itself from the actorList. After that, you can insert whatever else you want to happen when time has elapsed. I've included a "beep" just to show you where to insert your additional instructions.

If the time has not fully elapsed, then it does the percentage calculation, comparing ticks elapsed to total ticks specified. This percentage is then applied to the width/height -- either positively or negatively (depending on whether it's counting up or down.)

Here's an interesting thing about the actorList. Once you add the behavior to the actorList, it will remain in existence even if the sprite goes away. So, if you start this behavior and it gets added to the actorList, it will persist even if you move to another place in the score -- or ever to another movie. That could screw you up if you didn't realize what was happening. Therefore, I've included the endSprite handler that deletes it from the actorList.

One final thing to note is the getPropertyDescriptionList handler. For pOrientation and pDirection, I wanted to have 2 specific choices. For example, the orientation can only be either horizontal or vertical, and it's great to have these choices on a pulldown menu. To do that, specify a #range as a list [#horizontal, #vertical]. I went one step further. I wanted the behavior to be smart enough to guess whether the orientation should be vertical or horizontal. So, instead of specifying one or the other as the default, I used a variable called defOrientation.

The first few lines of the gpdl handler compare the width and height of the member in the current sprite. If height is more than width, then it guesses that the defOrientation should be #vertical. Otherwise, it's #horizontal. Try this feature for yourself by dropping the behavior first onto a wide sprite, then onto a tall one. The default in the dialog box will know which way to go -- though you can override it, of course.

One last note. In my demo, the horizontal bars are "anchored" to the left side, and the vertical bars are locked to the bottom of the range. You can change this by resetting the regPoint of the cast member. In the demo above, the horizontal cast member has a regPoint of point(0,0) -- top left. The vertical members have a regPoint set to the bottom left corner. Play with the regPoint to come up with variations which meet your needs.

Good luck with your project.

Patrick McClellan is Director Online's co-founder. Pat is Vice President, Managing Director for Jack Morton Worldwide, a global experiential marketing company. He is responsible for the San Francisco office, which helps major technology clients to develop marketing communications programs to reach enterprise and consumer audiences.

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