bounds, AABB and AABBLike

[dennemark]

Hi,
I want to do bounding box intersection check.
I am providing bounds some points bounds(points3(myPoints)) but it returns an AABBLike.
If i want to use the result within intersectionAABB typescript complains that it is not an AABB type.
What is the purpose of AABBLike? Couldnt we just return an AABB from bounds? Right now i am doing the following: aabb(bounds(....))`

Or is the main reason that I have to decide afterwards, if I want to have a rect (2D) or an aabb (3d) ?

Kind regards!

[postspectacular]

Hi Martin - the purpose of the AABBLike interface is a generalization for both 2D/3D cases and it's currently implemented by both the Rect (for 2D) and AABB (for 3D) classes. The bounds() function is polymorphic and dynamically chooses the right impl based on given inputs, but TypeScript only allows to specify a single return type (hence the AABBLike to satisfy both dimensions). In your case, bounds() will delegate to an implementation for points3 and does actually return an AABB shape instance, but again, the bounds() function's return type is more general...

So to use the result with intersectionAABB() you just need to add a manual cast to <AABB>, but do not require a separate coercion via aabb(...), i.e. you only need this:

intersectionAABB(
  <AABB>bounds(points3(myPoints)),
  <AABB>bounds(points3(myOtherPoints))
);

I should update the bounds() docs to better clarify what is being returned, i.e. a Rect instance for all 2D shapes and an AABB for 3D cases... There're some cases (e.g. empty groups) where the result can also be undefined...

[dennemark]

Ah this is convenient! I thought bounds might only return an interface, without functionality. But now it makes sense!
I am using typescript for a while now, but wasn't aware that this kind of casting is possible, too <AABB>bounds.

[postspectacular]

Just to add here: An interface/type only exists during authoring/compiling. It's best to think of them as contracts. A value/object either satisfies the contract or not. At runtime there're only values (no more types). Class instances in JS are just objects and to be compatible with an interface, they only must conform to the shape/structure of that interface/type (hence TypeScript is also known as structurally typed language, in contrast to say Java or C++, which are statically typed, with more limitations)...

So when we say here that bounds() has an AABBLike return type, you should read it as a value which satisfies the contract of the AABBLike interface, but provides no other promises or known features:

umbrella/packages/geom-api/src/shape.ts

Lines 18 to 24 in 6e20f80

	export interface AABBLike extends IShape<AABBLike> {
	pos: Vec;
	size: Vec;
	max(): Vec;
	offset(x: number): this;
	}