Highclip and lowclip seem not to work with volume

[Luluser]

Highclip and lowclip are not taken into account with volume recipes ?

vol = [cos(X) * sin(Y) * sin(Z) * T for X ∈ LinRange(0, π, 50), Y ∈ LinRange(0, 2π, 100), Z ∈ LinRange(0, 3π, 150)]
minmax = minimum(vol)*1.1, maximum(vol)*0.9
f= Figure()
ax= LScene(f[1,1])
plt = volume!(ax, vol, colorrange = minmax, colormap = :coolwarm, lowclip=:transparent, highclip=:black)
cb = Colorbar(f[1, 2], plt)

Give the proper colorbar but a plot ignoring the outside values

• Makie v0.21.13
• works with a fresh environment
• Ubuntu 22.04.5 LTS, Mesa Intel® Graphics (RPL-P)

[jmert]

I came across a use case where I wanted to use lowclip to make features in a volume plot more visible. Making a few changes to the GLMakie fragment shaders and the following test case,

Plotting code

using GLMakie

xx = range(-π, π, 300)
vol = [cos(x) * sin(y) * sin(z) for x in xx, y in xx, z in xx]
kws = (;
       colormap = :viridis,
       colorrange = (0.1, 0.9),
       lowclip = :transparent,
       highclip = :black,
      )

fig = Figure(size = (800, 600))

algorithms = (:mip, :absorption, :absorptionrgba, :additive)
for (ii, alg) in enumerate(algorithms)
    I = Tuple(CartesianIndices((2, 2))[ii])
    ax = Axis3(fig[I...], title = "algorithm = $(repr(alg))", aspect = :equal)
    volume!(ax, vol; algorithm = alg, kws...)
end

I can turn the first image into the second image.

Before

After

Going through this exercise, though, I realize it's not 100% clear to me what the interpretation of lowclip and highclip even are given the different algorithm options. If my (hacked) code changes are useful to further progress, I'd be happy to share/make a draft PR.