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implementing scripting system in C++ using LUA or Python


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#1 Kurasu1415   Members   -  Reputation: 152

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Posted 25 July 2013 - 01:12 AM

In the simplest terms, what is the common architecture that developers use to manage and persist script states in their games? Below is a better description of my issue.

I've doing a lot of research lately regarding exposing my c++ classes to either LUA or Python. I'm still not sure on what language I want to go with, but that isn't the real question. Exposing a class in either language is no problem, but what I don't understand is where to go from here.

What I don't understand is how people manage to get seemingly separate script states for every script instance in their game. For example, Every enemy in the game has a script, that defines a health variable for that enemy. So, if an enemy loses health, the next time I run his script, his health variable in the script should still show the health value it was previously.

I can see two obvious solutions to this problem.

#1. Have a different Lua interpreter for ever single instance. (This just seems needlessly expensive)

#2. Save the state of your entire interpreter and load that up for each script run.

The 2nd option seems like the best solution, but I have seen that this is a bad idea. Regardless, I did look into this, and it seems like using the Pickle library with Python would be a good solution. I have also seen that I could serialize parts of my Lua instance and store those.

What do you guys recommend  as the best solution?
 



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#2 Hodgman   Moderators   -  Reputation: 27586

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Posted 25 July 2013 - 01:47 AM

Don't think about each object "running a script" -- after all, when you write a C++ program for enemies in the game, you don't worry about how to make one enemy "run a program", and how to make another enemy have "it's own program".

 

Just think about some of your code being in one language, and some in another. Lua scripts == Python scripts == C++ code, they're all just code.

 

If in C++ you'd put health inside an enemy class, and then have 100 different instances of that class, then you can do the same in Lua or Python (possibly using tables/dictionaries if not classes)...



#3 Eden-san   Members   -  Reputation: 113

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Posted 25 July 2013 - 04:22 AM

Just like Hodgman said, it just works the same in script as it would in any other compiled language.
Just write objects and instantiate them, if you have any states that you want persistant just serialize them as binaries or XML, then reload them later on.



#4 Pink Horror   Members   -  Reputation: 1084

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Posted 31 July 2013 - 10:06 PM

I'm unaware of the specific details of doing this in Lua or Python, but you should be able to call the main AI function of the enemy script from your C++ code and pass the specific character in as an argument. Modify the character data to include whatever you want to persist.


Edited by Pink Horror, 31 July 2013 - 10:07 PM.





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