• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0
SeiryuEnder

Defining Entities using XML/Lua

2 posts in this topic

I've been developing a data-driven Entity/Component system in C++ using Lua. There's been a lot of good documentation out there, but I've hit a bit of a snag with Lua.


-edit 1:
[indent=1]My problem is likely to do with the need to bind classes to Lua rather than using a factory to create components... Still doing research on that[/indent]

-edit 2:
[indent=1]After some thought and playing with Luna, I'm going to try registering components with my factory and feeding the base pointer address back to Lua.[/indent]
[indent=1]From there I should be able to call the expected mapped function. I don't know what kind of error handling this will have (if any), but at least it's moving in a direction.[/indent]


[b]Summarized Question[/b]
How do I create objects with a C++ factory using Lua and define necessary parameters while maintaining type-safety?
My goal is to be able to determine at runtime if there is a parameter mismatch when defining a component.

[b]More Information[/b]
The system works like this:

Open OnLoad.lua
-OnLoad.lua loads _Level_.lua
--_Level_.lua loads and posititions Entities in the world
---Game parses XML file for (each) Entity definition

[One of two ways to handle this]

[i]A[/i]
----Entity tag references _Entity_.lua
-----_Entity_.lua loads components

OR

[i]B[/i]
----Entity tag body contains a list of components along with component property definitions

[b]Problem 1:[/b]
Not a huge problem, but a mild design question. Method A is more expandable (Lua can perform other actions when loading different types of entities, may be useful), but Method B is simpler and centralized. Right now I'm leaning towards defining entities in Lua to err on the side of caution, as I may need the extra functionality later. Which do you think is the preferable method?

[b]Problem 2:[/b]
I'm stuck on how to actually construct the components. I'm sure there's a simple solution, but for some reason it eludes me. Different components may need different parameters. For instance, I may need no parameters at all for a Timer component but will need a name/ID for a Mesh component. I'd like to figure out a way to register the component with my object factory but that would mean having to have a default constructor and defining a different Init(...) function for each type of component. When I create the object with the factory I will get a base class pointer back, so I have no (type-safe) way of knowing what parameters the init function will need. I'm just not making the connection on how to define properties of a component in XML/Lua then pass that information to its appropriate place in C++. I've considered more elaborate methods of defining property tables in my components, but that seems inefficient and overcomplicated.

As always, thanks in advance for any help! Edited by SeiryuEnder
0

Share this post


Link to post
Share on other sites
My main question is why are you using both XML and Lua? If you've already embedded Lua, you have at your fingertips an excellent [url="http://www.lua.org/pil/10.1.html"]data description language[/url], making any reliance upon XML completely redundant, and needlessly complicating things.

As for the rest of it, I'm not 100% sure what it is you're asking. Guess my reading comprehension fails today. If the problem is with actually binding classes to Lua, they have libraries for that including [url="http://www.codenix.com/~tolua/"]tolua++[/url] and [url="http://www.rasterbar.com/products/luabind.html"]luabind[/url].

I did a writeup on how I do things for my own projects [url="http://www.gamedev.net/blog/33/entry-2249433-how-goblinson-crusoe-works-the-tldr-version/"]here[/url], if you are curious.
0

Share this post


Link to post
Share on other sites
Yeah it's a bit of a complex problem to describe without coding examples.

The only real reason for using XML right now is that at some point I intend to support other scripting languages such as Python.
XML acts as a simple layer of abstraction between the game and the scripting language.

The problem was twofold - my lack of understanding how to properly use Lua and how to initialize my components.

For instance, until now I've done something like this (just to get things running):
[CODE]
Entity* ent = new Entity;
Cmp_Transform* cmpTransform = new Cmp_Transform( ent );
Cmp_Mesh* cmpMesh = new Cmp_Mesh( ent, "SomeMesh.gmx" );
ent->AttachComponent( cmpMesh );
ent->AttachComponent( cmpTransform );
ent->Initialize();
[/CODE]

I moved the constructor args to an Init function so that I could use the default constructor.
Now, I can register components to an object factory and create them like this:

[CODE]
Factory<IComponent*> factory;
factory.Register<Cmp_Transform>("Transform");
IComponent* cmp = factory.Create("Transform");

Entity entity;
entity.AttachComponent( cmp );
[/CODE]

With a simple glue function I can create any registered component by knowing its name, which gives me a lot of flexibility from the scripting end.
The problem was, I couldn't call an Init(...) function from the C++ end because it is a member function of an unknown derived class.

I think I've finally figured this one out. I've set up Luna to bind component member functions to Lua, and I'm going to push the component pointer onto the stack.
From there I should be able to call the Initialize function. I haven't gotten that far in code yet, but theoretically it should pipe to the proper function where I can at least check the number of arguments and hopefully later enforce better type safety. Edited by SeiryuEnder
0

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0