Scripting System Basics

Biggles · 2004-01-10T16:41:38

Apologies if this has been covered before, but I can''t seem to find any tutorials or threads that cover what I can''t figure out. Noone seems to cover the initial stuff. I''m trying to work out how to integrate a scripting system into my engine. At the moment the actual language used isn''t important (although FYI I''m considering python or lua). What I want to know is how the actual integration works. Here''s an example: I have a GUI system in the engine. I want to be able to create windows and menus using a config file (like xml or something, it doesn''t really matter what). I need to have the event functions for things like buttons execute user-defined (where user = game designer, not engine developer) code, and for that code to be executed when said button is clicked. The code would need to play with things in the engine (eg pop up a new (already defined in another config file) window, or change a graphics setting, or something like that) which means it needs to be able to change engine settings and interact with other objects in the system. Let''s say I have a window for configuring the video options. I would need the scripting code to be capable of populating certain parts of the window like list boxes (for resolution changes) and sliders and so forth. I would also need the code for the OnClick event of the OK button to be able to get the values of the list boxes, sliders, etc from them and update game settings with them. Another example would be when the user does something in the game world, like "use" an object. I would need to be able to run a block of code that would alter the game world in the way desired for when said object is used, which means the scripting system needs to be able to affect these objects in some way. So my question is (after that rather long winded paragraph) how does all this work? How exactly do I expose the required functionality in my (C++) engine? How do I run a block of code taken from a config file that says "when the object defined by this config file does this or is interacted with do this"? Links to tutorials/threads that I missed explaining this are welcome. Thanks in advance for any help. -------------------- Never eat anything bigger than your own head.

Engines and Middleware Programming

Started by Biggles January 07, 2004 03:20 AM

12 comments, last by Biggles 20 years, 3 months ago

Toni Petrina

123

January 08, 2004 12:38 PM

Looks like all you need is Python...

So... Muira Yoshimoto sliced off his head, walked 8 miles, and defeated a Mongolian horde... by beating them with his head?

Documentation? "We are writing games, we don't have to document anything".

stodge

144

January 08, 2004 12:51 PM

Check out:

http://habitat3d.sourceforge.net

It does pretty much the same thing you are trying to do.

---------------------http://www.stodge.net

Fruny

1,658

January 08, 2004 01:14 PM

quote:Original post by Biggles
for example, a C function used by the script to draw a rectangle on the screen would need to be able to access the display object, eg Display::DrawRect), which have been encapsulated inside the main engine class. How do I get around this problem without breaking encapsulation? Is it even possible?

Well, duh, you have to decide on whether you want the script system to be able to acces those classes and manipulate the entities they represent, or if they should be locked away.

Breaking encapsulation means you provide an access that can let a third party programmer leave your objects in invalid states (violate their invariant), for example, by changing values of internal pointers, without code that manages those pointers being notified (like the ''next'' pointers in a linked list). What you are doing is to add new functions that can manipulate the object, but which are still expected to leave the objects in a valid state (assuming they were in a valid state to start with, which is what encapsulation is intended to ensure). So your are just exposing a new (scripting) interface.

Implementation note: extern "C" static member functions can be useful when you need to write functions callable from C, that access private members of a class, without violating encapsulation. Obviously, being static, they need an object pointer (C doesn''t have references) among their arguments.

"Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." — Brian W. Kernighan

Biggles

122

Author

January 10, 2004 04:41 PM

OK, I think I understand how it all fits together now. Thanks for the help, everyone

--------------------
Never eat anything bigger than your own head.

--------------------Never eat anything bigger than your own head.

Scripting System Basics

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Scripting System Basics

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