Re: Scripting in games.

["J. Perkins" <jason@379.com>]

I have a bit of experience here, so I'll take a crack at it...


> * I could provide (for example) a function to position an object that 
> 'belongs'
>   to the script at a specified X,Y,Z,Heading,Pitch,Roll - but should I 
> instead
>   make the interface be Velocity+Direction and let the game do the 
> integration
>   down to positions - or perhaps the interface should just be a place to 
> head
>   towards and a choice of several 'modes' of getting there?

You'll probably all three approaches. A script might want to add a
new static object to the world (1), or maybe apply forces to all
dynamic objects to push them away from an explosion (2) or run a
pathfinding algo to get from a to b (3). Pathfinding is generally
too cpu-intensive to be coded in a script.


> * How should the game handle collision detection for scripted objects?   

Collision detection should happen in your C code (too slow for
scripts, and script writers don't want to be bothered). When a
collision is detected call a hit() function or similar on the
scripted object and pass it the object that it hit. The script
can then determine what to do about the contact.


> * How does the scripting interface deal with telling the script the 
> position
>   of the player and other creatures?

I have a FindEntity() that can locate another object by name.
The script can store a reference to the entity in a variable, and
then call GetPosition() etc. as needed. That is, the scripted
object should ask for what it needs.


> * Should scripts be able to communicate with each other?

If you allow this, it should definitely be through some sort of
indirection like messaging or an event system. That way a script
can safely ignore events that it doesn't recognize. For game objects
it's not too bad, because you can standardize the interface to
a "thing", but for the AI logic it does get kind of fuzzy. The
best bet is to keep object boundaries clear.


> How do existing games deal with this stuff?   Is there a 'classic' game
> somewhere with a scripting interface that's known for having "Got It 
> Right" ?

It has been my experience that the *best* way to this stuff is via
a plugin/component system. No matter how much stuff you give the
scripters, there will always be something you didn't think of.
Create a simple base of functionality, a standard object system
for your scripts, and a standard way to add to it.

A good place for info on these kind of things is the unrealtech page
at http://unreal.epicgames.com.

Jason
379