Add Basis2D

[Tameno-01]

In 3D, there's Transform3D and Basis, the former containing an instance of the latter.
In 2D there's just Transform2D, with no separation of the origin vector.

I think it would be better to:

• Add a Basis2D.
• Replace Transform2D's x and y properties with a Basis2D.
• Rename Basis to Basis3D.

This would be good for the following reasons:

• Makes 2D and 3D more consistent with each other.
• Makes code that deals with matrices and transforms more explicit.
• 2D matrix math doesn't have an origin that's just unused.
• Adds a better type to mirror mat2 in shader code.

I know this could be seen as trivial, but I don't see a reason to not do it either.
Obviously this would need to wait until Godot 5.0 since it breaks compatibility.

[AThousandShips]

What would be the existing or intended use case in the engine for this? For Basis there's a ton of uses where the engine wants a non-translational transform type, but I can't really think of any examples in 2D, where the translation is explicitly ignored as a sort of workaround, or where we instead pass the parts of a transform independently to avoid this

What would be the concrete uses for this, as opposed to consistency

[Tameno-01]

I'm making this proposal from the prespective of an end user, not an engine developer.

Any end user that wants to do do any matrix math involving directions, velocities, or really anything that's not a position, benefits from this.

But that's besides the point, consider this:
In the jump from godot 3 to godot 4, all the Spatial and all the nodes that inherit from it were renamed to Node3D and <name>3D respectively. Do you think this was a bad idea? There's no "concrete use case" for the rename, but it made 2D and 3D more consistent, made code more explicit and easy to read, and made names more intuitive and predictable for end users.

Yes, this is a minor improvement, but the cost of making said improvement is even smaller, just like renaming Spatial to Node3D.

[AThousandShips]

In the jump from godot 3 to godot 4, all the Spatial and all the nodes that inherit from it were renamed to Node3D and <name>3D respectively.

That's completely different and unrelated though? That was because of cleaner naming, this is a functional change which cannot be trivially upgraded with simple renames, and comes with overhead and complexity, requiring all code using Transform2D that would now be using the new Basis2D functionality to be rewritten

For the concrete use case for the 3D rename that was for organization and avoiding confusion, very real confusing among users

This would involve a lot of engine code changes to accommodate this, so there needs to be some concrete value in doing this

Basis has extensive uses outside of just manipulating 3D nodes, it's used extensively for XR and for rendering, the same cannot really be said for 2D, unless you can find some examples where it is important to discard the translation part of the transform

Adding a whole new built-in type comes with a lot of work, it adds a lot of new code for serialization, a decent amount of code to the GDScript parser and compiler, code related to rendering to transfer data types, and for extensions. In addition to making upgrading from 4.x to 5.x more difficult as all code using the old interface would have to be rewritten, and a lot of the time that would have to be done manually as it's not always possible to just replace one call with another

So there needs to be some real concrete reason this would be used, and that it would be used more than just now and again, beyond it just being useful

For the examples of doing matrix math, that's not really what the 3D basis is for, it's specifically for 3D transforms and doesn't support most generalized matrix mathematics, the same would apply for a 2D equivalent. There's also not really much difference between just using Transform2D, you don't even save any memory using GDScript as Variant is padded to the minimal stored size, which means that it will always take up at least as much space as Transform2D anyway (actually a lot more, at least enough for Projection). The difference in performance of skipping the translation wouldn't be significant at least not when running GDScript as a few float additions are negligible compared to the overhead of GDScript itself

[aaronfranke]

Regardless of the addition of Basis2D, I am highly in favor of renaming Basis to Basis3D for consistency with Transform3D, Node3D, and so on. Also I'm biased because in my 4D module I have a Basis4D type, so it helps with clarity.

[AThousandShips]

That makes a lot of sense in itself, it would be minimally disruptive for 5.0 with just rename support

[aaronfranke]

Another reason to rename Basis to Basis3D is to avoid public Basis Basis; in the C# code: https://github.com/godotengine/godot/blob/master/modules/mono/glue/GodotSharp/GodotSharp/Core/Transform3D.cs#L27

When writing C# code that uses this, you need Godot.Basis to unambiguously refer to the type, or something.Basis (such as this.Basis) to unambiguously refer to the variable.

[Jesusemora]

2D only has one axis, because if you were to rotate in some Y axis, you would be doing scale.
3D needs basis for rotation because it has 3 axes, "more" if we use quaternions. 3D can have rotations in 4 axes, and scale applied at the same time.

[AThousandShips]

It is relevant to handle computations a bit more efficiently and complex combinations than scale + rotation + shear, but it's far less critical