Allow arrows to take a Function to produce the vector

[asinghvi17]

Description

Allow arrows to take input of the form x::AbstractVector, y::AbstractVector, [z::AbstractVector,] f::Function

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Type of change

Delete options that do not apply:

• New feature (non-breaking change which adds functionality)

Checklist

• Added an entry in NEWS.md (for new features and breaking changes)
• Added or changed relevant sections in the documentation
• Added unit tests for new algorithms, conversion methods, etc.
• Added reference image tests for new plotting functions, recipes, visual options, etc.

[ffreyer]

Shouldn't that be Point2f.(x, y)?

[asinghvi17]

No, arrows always creates a matrix - the eventual positions are Point2f.(x, y') anyway. Plus the inputs are AbstractVectors so we know that we have to make the grid.

[ffreyer]

Hmm, it does one or the other depending on the type of directions:

Makie.jl/src/basic_recipes/arrows.jl

Lines 105 to 108 in c03f7a5

	convert_arguments(::Type{<: Arrows}, x, y, u, v) = (Point2f.(x, y), Vec2f.(u, v))
	function convert_arguments(::Type{<: Arrows}, x::AbstractVector, y::AbstractVector, u::AbstractMatrix, v::AbstractMatrix)
	(vec(Point2f.(x, y')), vec(Vec2f.(u, v)))
	end

That makes this a bit awkward to reason with...

[ffreyer]

To me it seems more intuitive to just directly pass on args rather than doing a conversion beforehand. I.e.

arrows(xs, ys, (xs, ys) -> Vec2f.(-ys, xs))

rather than

arrows(xs, ys, ps -> Vec2f[(-p[2], p[1]) for p in ps])

That seems to be what surface and volume do.

I also wonder if we should just have a default conversion of (args..., f) -> (args..., f(args...)) for all plot types.

[asinghvi17]

I do like the idea of that second conversion - but it might be easier to implement it per plot type.

[SimonDanisch]

Closing in favor of #3080