[gameprogrammer] Re: Level triggered data synchronization
- From: Bob Pendleton <bob@xxxxxxxxxxxxx>
- To: Gameprogrammer Mailing List <gameprogrammer@xxxxxxxxxxxxx>
- Date: Wed, 21 Apr 2004 09:09:46 -0500
On Tue, 2004-04-20 at 23:31, Kevin Jenkins wrote:
> While working on my game I (now) consistently use a programming design
> that makes it easier to write and maintain code.
>
> I call it level triggered data synchronization. By level triggered I mean
> as opposed to edge triggered - data changes during processing rather than
> when the event to change the data occurs.
>
> The concept is quite simple. When you have a variable that you can set
> based on the current program state you should recreate the value for that
> data every cycle rather than setting that data on the conditions that
> directly modify it.
>
> For example, lets say you have a program where the user clicks on one of 3
> filenames and a bitmap shows up to display the filename chosen.
>
> To program this using edge triggered data synchronization, you would put
> code in the MousePress function. Depending on which filename was clicked,
> you immediately load that file and unload the older image if necessary.
>
> To program this using level triggered data synchronization, you would put
> code in the Render function. The render function would check the variable
> containing the index of which filename was picked. It would then compare
> this filename what Bitmap::Name() returns. If they are different, or if the
> bitmap is NULL, then load the new image.
>
> The second way is slightly less efficient because you are doing a comparison
> every frame. However, it is far more maintainable because if at a later
> point you add another place to show another image it will show the correct
> image for free. In the first case, you would either cut and paste the code
> to load the image or at best call a function, assuming (in the unlikely
> case) that you made this a function to begin with or put it in a function to
> avoid code duplication.
There is a different term for this, I can't remember it, but there is
another name for it. You have discovered on your own a principle that
many programmers "don't get" even when it is pointed out to them.
Thanks for posting it.
Bob Pendleton
>
> Another benefit of the second way is you sometimes avoid processing. For
> example, lets say there were two places you could pick the same bitmap. If
> you picked the new bitmap that had the exact same path/filename as the old
> one,
> it would avoid an unnecessary load.
>
> In trivial cases both ways works fine. But in large classes with many
> variables this can cut down on a lot of code and maintenance. It also makes
> the program more maintainable if someone else has to work on it because they
> can change one section of the code and it just works - as opposed to working
> in some cases and not others. Of course when it takes a lot of processing
> to determine the state then stay with edge triggered. But in most cases
> it's as simple as checking a few pointers.
>
> I'm sure a lot of people know this. The reason I point it out is because I
> didn't strictly follow it before and now I do and have really seen the
> benefit.
> I think it's important enough to point out.
>
--
+---------------------------------------+
+ Bob Pendleton: writer and programmer. +
+ email: Bob@xxxxxxxxxxxxx +
+ web: www.GameProgrammer.com +
+---------------------------------------+
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