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Choosing a game engine for an open Roblox/Kodu/Lego Worlds/LittleBigPlanet-like app


 
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Duncan Cragg (Duncan Cragg)
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Joined: 26 Apr 2017
Posts: 2

PostPosted: Wed Apr 26, 2017 8:52 pm    Post subject:
Choosing a game engine for an open Roblox/Kodu/Lego Worlds/LittleBigPlanet-like app
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Hi everyone!

I'm looking for a game engine that's suitable for an Open Source app that I want to write and share on GitHub. I'm evaluating Godot, Atomic, Urho3D, Blender and OpenSceneGraph. I'm hoping some of you here can help me determine if this engine is a candidate Smile I'm not 'hawking' my game idea, and sincerely hope this is the right sub-forum!

My idea for the app is "building and programming your own games - without needing technical skills" - along the lines of: Roblox, Kodu, Lego Worlds, LittleBigPlanet, Struckd, Blockland (apparently defunct), Project Spark (defunct).

It will have a simple rule programming language to bring things to life. Aside from the app being Open Source, this language is the main differentiator to these other approaches. It isn't text-based, it appears as simple 2D grids expressing rules, that are similar to spreadsheet formulae, and that react to scene object state changes.

The game engine should thus ideally make the following elements nice and easy:
    - 2D interface panels...
    - with scrollable selectors, grids holding text items, buttons
    - to choose and configure renderable game objects into scenes
    - to enter and edit the animation rules for those objects
    - that either pop up over the live scenes or appear inside them
The last point in the list above is because the rule editor, rule runner and game loop won't be started and stopped, they will run continuously, even as rules are being updated.
    - API access to the states of scene objects, to read and write their properties and be notified of events
    - persistence of scene structures and their rules to a database or files
    - access to threads and the event loop to give my stuff plenty of CPU
    - easy API access and C/C++ code extension
    - building to Android and other common platforms
I would strongly prefer to write the rule runner in C, rather than C++. I've implemented similar systems in every language known to man, including these three, but C feels like the right low-level language to implement another very high-level language in. This is partly because of speed and resource usage, but also because C is very portable, so I'd find it easy to port the language to any other hardware or OS, including embedded systems, etc. Having said that, I'm open to strong arguments in favour of C++.

So my question is, can OSG easily support the bullet points above? Very Happy

Duncan
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Alistair Baxter
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PostPosted: Thu Apr 27, 2017 8:35 am    Post subject:
Choosing a game engine for an open Roblox/Kodu/Lego Worlds/LittleBigPlanet-like app
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"So my question is, can OSG easily support the bullet points above?"

No, I'm afraid it can't.

OpenScenegraph isn't a game engine, it's just a set of tools for representing and rendering 3D scenes, that could be used by one, plus some import and export tools. Although it does contain a simple UI toolkit, and quite a few plugins for interoperability with other software.

If you require doing a lot of UI for your programming language bit, and cross-platform compatibility, I'd have a look at Qt. It can be combined with OpenScenegraph, and made to run on Windows, Mac, Linux, iOS and Android (UWP is apparently in development for OSG and already available for Qt). Alternatively they have a scenegraph of their own.

However, either of these plans will still require you to write the engine parts of the game engine underneath them, or find extra bits of middleware like Bullet physics, which has an existing integration with OSG.


Incidentally, unless you're planning on porting to some *incredibly* obscure or ancient systems, C++, in fact the C++ 11 standard seems to be perfectly well supported across all today's popular platforms.





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robertosfield
OSG Project Lead


Joined: 18 Mar 2009
Posts: 10892

PostPosted: Thu Apr 27, 2017 9:50 am    Post subject:
Choosing a game engine for an open Roblox/Kodu/Lego Worlds/LittleBigPlanet-like app
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Hi Duncan,

The OSG could be used for sure, I'm not familiar with the alternatives
so can't compare, but in general you might find the OSG quite low
level - it's a scene graph rather than application or game framework,
so it's a component of such a framework rather a high level framework
itself. This is both and advantage and a disadvantage, if you need to
flexibility then lower level is good, if you want off the shelf high
level features then perhaps high level framework would be appropriate.

When looking at the OSG, it has the portability covered pretty well,
it's always very flexiblity and powerful, so unlikely to constrain you
in what you want to achieve. Specifically for your project one asset
might be the osgDB::ClassInterface that was introduced in OSG-3.4.
This would provide a single class for doing introspection,
setting/getting properties, creating objects. The ClassInterface also
provides the mechanism which the ScriptEngine implementations can wire
up the OSG's C++ objects with other languages.

In OSG-3.4 we have a lua plugin that provides the lua language
interpreter built in and integration with the
ScriptEngine/ClassInterface so that you can create, add callbacks,
read/write properties all from with lua scripts.

Quote:
From your description perhaps lua itself might be a useful tool, so
write the bulk of your application in lua and have it control the
OSG's scene graph.

Robert.


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Duncan Cragg (Duncan Cragg)
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Joined: 26 Apr 2017
Posts: 2

PostPosted: Fri Apr 28, 2017 9:50 pm    Post subject:
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Thanks to you both for your detailed replies and the trouble you took over writing them. Very much appreciated! Very Happy

After doing some more research, I think I do want the ease of something that includes more and works at a higher level, so my current favourite is Godot, which is very active and, to be honest, will save me a lot of work!

Thanks again, and I hope all goes well with OSG!

Cheers!
Duncan
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