Add fill method to Arrays and PackedArrays

[DarknessCatt]

Closes godotengine/godot-proposals#2181
Based on the discussion on #46173

Adds a fill(value) method for Arrays and PackedArrays that allows filling the entire array with a single value.

Example usage:

var arr = Array()
arr.resize(4)
arr.fill(3.14)
print(arr) # [3.14, 3.14, 3.14, 3.14]

I would also like to thank @anberino. He ran all tests for me (since my gpu doesn't support vulkan) and this PR wouldnt be possible without his help.

[Xrayez]

I'm not sure about the extra logic for duplicating container types. Things like Array are passed by reference and is documented behavior, so I'd expect fill() to allocate needed elements to hold the same Array reference. Perhaps this can be made configurable. But I find it difficult to find a use case for filling an array elements with arrays/dictionaries, I think in most cases the method would be used by structures which are passed by value rather than reference.

[DarknessCatt]

While I agree it's a bit counter intuitive to duplicate, I though it would be a little weird to have an array where every position is the same object.

However, I can make it optional or simply remove the duplication, If requested.

[DarknessCatt]

Due to the reasons pointed by @Xrayez, I've removed the duplication on container types.

This should make the method more consistent and avoid future bugs related to duplicate(...).

[Xrayez]

I suggest refactoring the code this way:

// vector.h

template <class T>
void Vector<T>::fill(T p_elem) {
	T *p = ptrw();
	for (int i = 0; i < size(); i++) {
		p[i] = p_elem;
	}
}

// array.cpp

void Array::fill(const Variant &p_value) {
	ERR_FAIL_COND(!_p->typed.validate(p_value, "fill"));
	_p->array.fill(p_value);
}

1. Eliminates code duplication.
2. Improves performance. set() uses a write() proxy on each element access. Using ptrw() allows to modify the vector's contents directly. I've got x3 speed up on my machine on large arrays this way (tested on PackedByteArray).
3. Consistent with other Array method implementations.

[DarknessCatt]

Thanks for the feedback, @Xrayez.

I've updated the code and the documentation with your chances. I've also added the documentation for PackedVector2Array and PackedVector3Array, since I forgot to add them in the previous commits.

[akien-mga]

Sounds like this was adapted from the insert description, that doesn't sound clear to me. I'd suggest instead:

Suggested change

	Inserts a new element at every position of the array.
	Initializes all elements in the array with the given value. This can typically be used together with [method resize] to create an array with a given size and initialized elements:
	[codeblocks]
	[gdscript]
	var array = []
	array.resize(10)
	array.fill(0) # Initialize the 10 elements to 0.
	[/gdscript]
	[csharp]
	var array = new Godot.Collections.Array{};
	array.Resize(10);
	array.Fill(0); // Initialize the 10 elements to 0.
	[/csharp]
	[/codeblocks]

[akien-mga]

The code example might not need to be added to all Packed*Array equivalent descriptions though, might be a bit redundant.

[DarknessCatt]

Indeed, it was adapted from insert. I will update the descriptions ASAP, but I might change the word "initialize" to something else. I don't know if it's just me, but it gives me the ideia of something that you do when creating the array, but you can call array.fill() whenever (you could use it to "reset" an array or something).

[akien-mga]

Yes it could be "Sets all elements in the array to the given value." or "Assigns the given value to all elements in the array."

[DarknessCatt]

I've updated the documentation. Thanks for the help and suggestions!

[akien-mga]

Just missing a dot at the end of the sentence for all Packed*Array descriptions, otherwise it's all good.

[DarknessCatt]

Oh yeah, my fault for copy pasting and not double checking. Thanks for the heads up, it's should be fixed now.

[akien-mga]

Thanks!

[Zireael07]

Can this get backported to 3.x?

[Calinou]

Can this get backported to 3.x?

Yes, but this PR needs to be manually redone for 3.x.