[simspark-devel] APL Design

[<ah...@un...>]

Hello,

After taking a long and careful look at the source code and thinking about
the greater picture, here are my conclusions.

I'd like to (1) keep the current dependency tree for the abstract physics
layer and (2) go crazy on the multiple inheritances.

(1) - The current design is very well thought out and, more importantly,
many other parts of simspark expect it. Any major changes in the
dependency tree require adjustments in many other parts of the system,
mainly the parsers and other plugins that work with oxygen. Also, with an
abstract physics layer that stays true to the current design, it should be
easy to integrate the current ODE-specific code into it. Any changes to
the design require large parts of the current code to be rewritten - I can
tell this from first-hand experience because I've been trying to apply the
new design for about one and a half weeks before I decided to rethink it,
and I still had many unsolved problems despite only focusing on basic
functionality.

(2) - I think it's pretty easy to argue that multiple inheritances are
needed. As far as I know, there are only two ways for an object to call a
non-static method: To implement it itself, or inherit from a class that
implemented it. So, let's look only at PhysicsObject for now. It's a
simple class providing some functionality that is the same for every
physics object: finding out which space or world an object is in, or
converting its rotation Matrix to something that Salt can work with. All
these methods use ODE-specific code, so either every ODE-specific subclass
implements it itself, or an ODE-specific superclass is implement that only
ODE-objects, but not Bullet-Objects inherit from. The first possibility
would generate more than three thousand lines of redundant code - and
that's only talking about the ODE-specific part of the code equal for all
physics objects.
Also, multiple inheritances wouldn't be that convulted. The simple rule
would be that every engine-specific class would have to inherit from its
parent class, and all engine-specific subclasses of superclasses of its
parent class. Sounds confusing, but it's quite easy: E.g. ODEBoxCollider
would inherit from BoxCollider (parent class), and since Collider and
PhysicsObject are superclasses of BoxCollider, it would also inherit from
ODECollider and ODEObject.


I will discuss this design with Joschka tomorrow, but you're welcome to
tell us what you think, as well.


thanks,

Andreas