# GLMakie beginners help: Multiple sliders and an arrow

**URL:** <https://discourse.julialang.org/t/glmakie-beginners-help-multiple-sliders-and-an-arrow/92113>\
**Category:** New to Julia\
**Tags:** plotting, makie, glmakie\
**Created:** [December 25, 2022, 8:44pm UTC](https://discourse.julialang.org/t/glmakie-beginners-help-multiple-sliders-and-an-arrow/92113 "2022-12-25T20:44:15Z")\
**Posts on this page:** 1\
**Showing post:** 3

<div class="post-metadata">

**Author:** ![fatteneder](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fatteneder/32/33991_2.png) [@fatteneder](https://discourse.julialang.org/u/fatteneder)\
**Post date:** [December 25, 2022, 11:20pm UTC](https://discourse.julialang.org/t/glmakie-beginners-help-multiple-sliders-and-an-arrow/92113/3 "2022-12-25T23:20:34Z")

</div>

I wasn’t 100% sure what you asked for, but I crafted something anyways (based on the tutorial link you gave above):

```julia
using GLMakie
GLMakie.activate!()

################################################################################
# Sliders
################################################################################

# initialize plot

fig = Figure(resolution = (3840, 2160))

# add axis

ax1 = fig[1, 1] = Axis(fig,
    # borders
    aspect = 1,
    # title
    title = "Sliders Tutorial",
    titlegap = 48, titlesize = 60,
    # x-axis
    xautolimitmargin = (0, 0), xgridwidth = 2, xticklabelsize = 36,
    xticks = LinearTicks(20), xticksize = 18,
    # y-axis
    yautolimitmargin = (0, 0), ygridwidth = 2, yticklabelpad = 14,
    yticklabelsize = 36, yticks = LinearTicks(20), yticksize = 18
)

# darken axes

vlines!(ax1, [0], linewidth = 2)
hlines!(ax1, [0], linewidth = 2)

# create sliders

lsgrid = labelslidergrid!(fig,
    ["scale", "x-reference", "y-reference"], #edited from original
    Ref(LinRange(-10:0.01:10));
    formats = [x -> "$(round(x, digits = 2))"],
    labelkw = Dict([(:textsize, 30)]),
    sliderkw = Dict([(:linewidth, 24)]),
    valuekw = Dict([(:textsize, 30)])
)

# set starting position for slope

set_close_to!(lsgrid.sliders[1], 1.0)

# layout sliders

sl_sublayout = GridLayout(height = 150)
fig[2, 1] = sl_sublayout
fig[2, 1] = lsgrid.layout

# draw a function

x = -10:0.01:10
m = @lift($scale .* x.^2) #quadratic function #edited from original
line1 = lines!(ax1, x, m, color = :blue, linewidth = 5) #edited from original

# create listeners

scale = lsgrid.sliders[1].value #edited from original
xreference = lsgrid.sliders[2].value #edited from original
yreference = lsgrid.sliders[3].value #added 

# xreference, yreference are Float32s
# but for arrows! below we need vectors of Float32s, so we promote them here

# arrow base points
xbase = @lift([$xreference])
ybase = @lift([$yreference])

#new multi-variable scalar-valued functions
p(x,y,scale) = (x + scale * y-1)^2/(scale^2) #added
z(x,y,scale) = cbrt(-p(x,y,scale)/2) #added

# arrow head points
# note: here we also return vectors
xhead = lift(xreference, yreference, scale) do x, y, s
    return [x/1 + 2*s * z(x,y,s)]
end
yhead = lift(xreference, yreference, scale) do x, y, s
    return [y + z(x,y,s)]
end

arrows!(ax1, xbase, ybase, xhead, yhead)

display(fig)

```

The above gives you now the arrow you can control with the sliders. Maybe you need to tune the computation of the end points a bit, because right now it does not seem to make any sense to me 😆

Modifications I made to your code:

- You can’t use `-` in variable names, so I renamed `x-reference` to `xreference`, etc.
- I replaced `:fontsize` with `:textsize`, because that was changed recently, but you might be running an older version of Makie.
- Arrows can be drawn with `arrows`, cf. [arrows - Beautiful Makie](https://beautiful.makie.org/dev/examples/generated/2d/arrows/arrows/?h=arrow). For this to work, one has to pass `Vector{Float32}` (or Observables thereof) to `arrows!`. Hence, I add an extra `lift` for that to promote the `xreference, yreference`. The reason it wants a Vector instead of a single number for each component is that `arrows` is optimized to draw vector fields, see the link above.

Last remark: Next time please provide a minimal working example (MWE) of the code that is already working and others can then use to build on top off.

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