Support for Unitful.Gain in axis recipes?

[icweaver]

Feature description

Would it be possible to add Unitful.Gain to the list of supported units in unitful-integrations.jl?

We're investigating transitioning some of our JuliaAstro plotting infra over to Makie.jl, but are currently hitting this issue when trying to work with units that are not Quantities, which comes up when dealing with magnitudes in UnitfulAstro or logarithmic units in base Unitful for example:

julia> using GLMakie, Unitful

julia> scatter((1:10)u"dB")
ERROR: ArgumentError:     Conversion failed for Scatter (With conversion trait PointBased()) with args: Tuple{Vector{Gain{Unitful.LogInfo{:Decibel, 10, 10}, :?, Int64}}} .
    Scatter requires to convert to argument types Tuple{AbstractVector{<:Union{Point2, Point3}}}, which convert_arguments didn't succeed in.
    To fix this overload convert_arguments(P, args...) for Scatter or PointBased() and return an object of type Tuple{AbstractVector{<:Union{Point2, Point3}}}.`

Stacktrace:
 [1] conversion_pipeline(P::Type{…}, used_attrs::Tuple{}, args::Tuple{…}, kw_obs::Observable{…}, args_obs::Tuple{…}, user_attributes::Dict{…}, deregister::Vector{…}, recursion::Int64)
   @ Makie ~/projects/Makie.jl/src/interfaces.jl:241
 [2] conversion_pipeline(P::Type{…}, used_attrs::Tuple{}, args::Tuple{…}, kw_obs::Observable{…}, args_obs::Tuple{…}, user_attributes::Dict{…}, deregister::Vector{…}, recursion::Int64)
   @ Makie ~/projects/Makie.jl/src/interfaces.jl:233
 [3] conversion_pipeline(P::Type{…}, used_attrs::Tuple{}, args::Tuple{…}, kw_obs::Observable{…}, args_obs::Tuple{…}, user_attributes::Dict{…}, deregister::Vector{…})
   @ Makie ~/projects/Makie.jl/src/interfaces.jl:213
 [4] (Scatter)(user_args::Tuple{Vector{Gain{Unitful.LogInfo{…}, :?, Int64}}}, user_attributes::Dict{Symbol, Any})
   @ Makie ~/projects/Makie.jl/src/interfaces.jl:273
 [5] _create_plot(F::Function, attributes::Dict{Symbol, Any}, args::Vector{Gain{Unitful.LogInfo{…}, :?, Int64}})
   @ Makie ~/projects/Makie.jl/src/figureplotting.jl:316
 [6] #scatter#54
   @ ~/.julia/packages/MakieCore/sHgwT/src/recipes.jl:510 [inlined]
 [7] scatter(args::Vector{Gain{Unitful.LogInfo{:Decibel, 10, 10}, :?, Int64}})
   @ MakieCore ~/.julia/packages/MakieCore/sHgwT/src/recipes.jl:508
 [8] top-level scope
   @ REPL[6]:1
Some type information was truncated. Use `show(err)` to see complete types.

At any rate, #3226 has been a game changer for working with Unitful.jl, thank you for adding this support!

For plot types, please add an image of how it should look like

julia> using GLMakie, Unitful

julia> scatter((1:10)u"m")
# but replace "m" with "dB" or "mag"

[asinghvi17]

It seems like that would be pretty simple to add along with some function overloads on our end. I'm not a Unitful expert, but if you'd like to have a go at this I'd be happy to support from our end.

[ffreyer]

Maybe just needs to be added to

Makie.jl/src/dim-converts/unitful-integration.jl

Line 5 in 2fe1ac4

const SupportedUnits = Union{Period,Unitful.Quantity,Unitful.Units}

?

[icweaver]

Thanks all for taking a look and for the quick feedback!

oof, I was hoping that we could just update SupportedUnits too, and maybe add Gain/LogScale specific methods for base_unit, unit_string, and friends, but it looks like there are a fair number of other places in unitful-integration.jl that I think might need some special treatment for this type.

For example, it seems that I am running into JuliaPhysics/Unitful.jl#463 when best_unit tries to find the average of two decibel values:

Makie.jl/src/dim-converts/unitful-integration.jl

Lines 93 to 94 in 2fe1ac4

	function best_unit(min, max)
	middle = (min + max) / 2.0

i.e., it seems that things like

julia> using Unitful

julia> (1u"dB" + 5u"dB") / 2.0
ERROR: no automatic promotion of Gain{Unitful.LogInfo{:Decibel, 10, 10}, :?, Int64} and Float64.

are not currently supported in Unitful (although I guess this part could be worked around by just multiplying by 0.5 instead?) nvm, decided to just totally sidestep this in the PR

Additionally, it seems there are places where Makie tries to convert things to Quantities:

Makie.jl/src/dim-converts/unitful-integration.jl

Lines 158 to 161 in 2fe1ac4

	function update_extrema!(conversion::UnitfulConversion, value_obs::Observable)
	conversion.automatic_units || return
	eltype, extrema = eltype_extrema(value_obs[])
	conversion.extrema[value_obs.id] = promote(Quantity.(extrema)...)

which doesn't play nicely with Unitful.LogScaled subtypes.

Is this a blocker for trying to support these kinds of logarithmic objects in Makie?

[icweaver]

At any rate, here's a suuuper rough first attempt. Will continue the convo over there if this still seems like a worthwhile pursuit 👍🏾