Heritable trait based property inheritance systems

[james7132]

Objective

First/naive attempt to generalize transform_propagate_system for any inheritable component.

Solution

• Add a Heritable trait that defines the inheritance behavior across a hierarchy. GlobalTransform implements this trait.
• Generalize transform_propagate_system using Heritable as generic systems.
• Add extension trait for App for inserting these systems into the schedule.
• Add dedicated system labels for scheduling.

This implementation includes the optimizations found in #4180.

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There are a few drawbacks to this naive approach (originally detailed here: #4213 (reply in thread))

There are a few things to note with this initial set of assumptions if we are to generalize the existing transform_propagate_system.

• Root queries are no longer sufficient unless we allow skipping levels. transform_propagate_system relies on every Entity from the root to the leaf to have the inheritable components.
• Allowing skipping levels requires full hierarchy traversals for all inheritance systems, not just the hierarchies with the components present, which would negatively impact performance.
• Top down inheritance is the only mode supported. Bottoms-up composition (i.e. AABBs as a BVH) isn't well supported. This could be supported via a different trait if need be.

Followup Work

Implement this for Visibility and ComputedVisibility. Will likely need to work with existing systems for computed visibility in some way.

[superdump]

‘Heritable’ is an odd word to me. I would have expected ‘Inheritable’. However, I feel like ‘Hierarchical’ or ‘Hierarchic’ might be a better fit semantically. Hmm.

[james7132]

‘Heritable’ is an odd word to me. I would have expected ‘Inheritable’. However, I feel like ‘Hierarchical’ or ‘Hierarchic’ might be a better fit semantically. Hmm.

Heritable

• (of a characteristic) transmissible from parent to offspring.

Seems pretty apt to me.

[ickk]

I'll throw in 'Hereditary' for good measure 😂

Heritable and inheritable are synonyms, a bit like flammable and inflammable. Personally I would err on the side of 'inheritable' because it's far more common.