Confusing pen and fill behaviour for vector heads

[adigitoleo]

Vector head fill and pen behaviour is inconsistent depending on nesting in the arrow NamedTuple.
Ideally, I would suggest to make it work only inside arrow, and disallow pen and fill keywords outside that context.
This makes it logically consistent: all arrow head properties are set inside arrow.
However, other functions accept pen and fill keywords also, so I'm not sure of the best solution.

using GMT

function example_data()
    Gz = gmt("grdmath -R-2/2/-2/2 -I0.1 X Y R2 NEG EXP X MUL =")
    Gdzdx = gmt("grdmath ? DDX", Gz)
    Gdzdy = gmt("grdmath ? DDY", Gz)
    return Gdzdx, Gdzdy
end

function test_arrow_fill()
    subplot(grid = "2x2", panels_size = 10, name = "test_arrow_fill.png")
    dx, dy = example_data()
    subplot(:set, panel = 1)
    grdvector(
        dx,
        dy,
        inc = 0.3,
        arrow = (; length = 0.4, shape = 0, stop = true, norm = 0.4, pen = :cyan, fill = :red),
        linewidth = 1,
    )
    subplot(:set, panel = 2)
    grdvector(
        dx,
        dy,
        inc = 0.3,
        arrow = (; length = 0.4, shape = 0, stop = true, norm = 0.4, fill = :red),
        pen = :cyan,
        linewidth = 1,
    )
    subplot(:set, panel = 3)
    grdvector(  # Produces the expected result.
        dx,
        dy,
        inc = 0.3,
        arrow = (; length = 0.4, shape = 0, stop = true, norm = 0.4, pen = :cyan),
        fill = :red,
        linewidth = 1,
    )
    subplot(:set, panel = 4)
    grdvector(
        dx,
        dy,
        inc = 0.3,
        arrow = (; length = 0.4, shape = 0, stop = true, norm = 0.4),
        fill = :red,
        pen = :cyan,
        linewidth = 1,
    )
    subplot(:end)
end

test_arrow_fill()

[joa-quim]

I see. Yes, confusing but we are obliged to use at least one of fill or pen outside arrow() otherwise GMT barfs with

grdvector [ERROR]: Must specify at least one of -G, -W, -C

Need to work out some trickery here.

[joa-quim]

Can you please try #754 ?
It turns out that grdvector -W seems to be mandatory (looks like a bug to me), and since -Q (arrow()) is optional I didn't drop the fill and pen options from the base grdvector options, but I made them optional. Now you can set the fill and pen only from inside arrow(), or alternatively from base grdvector.

[adigitoleo]

According to discussion in the linked PR, I've opened two related issues on the GMT tracker:

• Vector head pen overrides vector stem defaults gmt#5997

• can't set vector head fill or pen without -W or -G options gmt#5998

[joa-quim]

I opened a related (double) issue too GenericMappingTools/gmt#5988, including the transparency, which is already fixed.

[adigitoleo]

Ah, oops I missed that one when I was looking through the tracker... Nice that the transparency is fixed.

[adigitoleo]

OK I think this can be closed, the fixes have been released in GMT 6.3 upstream.