Re: [GD-General] Multiple Inheritance and RTTI

[Noel L. <ll...@co...>]

On Wed, 05 Feb 2003 23:24:54 +0200
Peter Dimov <pd...@mm...> wrote:

> > Every frame we quickly cull out any scene nodes that are not visible
> > from a camera, and then for each scene node we query to see if they
> > implement the IRenderable interface.  If they do, they get a render
> > call.
> 
> Yes, I envisioned something like that.
> 
> What are the advantages of this approach over just providing a (possibly
> empty) render() in every node type? A virtual call can never lose to a QI +
> test + potential call.

Clearly, it's not there for performance reasons. The main thing it buys
us is some clarity (and maintainability) by keeping the interface of
each type of scene node to a minimum size. Especially if you use many
potentially different interfaces, things could get pretty cluttered.

It also makes it easier to create new types of objects. If I create a
new scene node I might not be sure exactly what functions I need to
override so it renders correctly. As soon as I inherit from IRenderable
things are very clear (and if they aren't, the compiler will remind me
to implement all those pure virtual functions).

In our case we ended up not having as many different types of scene
nodes or as many different interfaes as I initially anticipated, so we
could very well have folded the few functions in IRenderable back into
the SceneNode class.

I think that another potential advantage is that the QueryInterface
method might work better in a very heterogeneous environment, where you
are manipulating objects of all sorts of types, without a common base
class. Requiring that they all implement all the possible common
functions would be a total pain. But I haven't seen that in practice.


--Noel
ll...@co...