basic improvements for docs

[SimonDanisch]

No description provided.

[ffreyer]

I don't like using material as a faceview example. That's not something that changes on such a low level imo. Like a loaf of bread is gonna be made out of bread no matter where you look at it, even if details like color, roughness, reflectivity etc change. Material details changing per face also seems odd to me.

Maybe we can just remove the association with materials here and directly have reflectivity etc as vertex/face attributes? Or use something else as an example, e.g. color?

[ffreyer]

The way I envisioned materials to be used is to mark sections of the mesh with views and have corresponding materials in a metamesh. E.g.:

using GeometryBasics
using Colors

struct Material
    color::RGB{Float32}
    diffuse::Float32
    specular::Float32
    shininess::Float32
end

head = GeometryBasics.mesh(Sphere(Point3f(0), 0.3))
needle = GeometryBasics.mesh(Cone(Point3f(0, 0, -0.2), Point3f(0, 0, -2.0), 0.1))

pin = MetaMesh(
    merge([head, needle]),
    materials = [
        Material(RGB(1, 0, 0), 0.8, 0.4, 4.0),
        Material(RGB(0.8, 0.8, 0.8), 0.4, 2.0, 64.0),
    ]
)

# contains two ranges, one for the faces from sphere, the other for faces from cone
pin.views
pin[:materials]

using GLMakie
f = Figure()
a = LScene(f[1, 1])
# This basically undoes the merge, could also pass pisitions, normals etc as usual and faces as `faces(pin)[pin.views[i]]`
submeshes = GeometryBasics.split_mesh(pin.mesh)
for (m, material) in zip(submeshes, pin[:materials])
    Makie.mesh!(
        a, m, color = material.color, diffuse = material.diffuse, 
        specular = material.specular, shininess = material.shininess
    )
end
f

Iirc obj/mtl loading has another step of indirection here, where views correspond to material names which are used to look up materials in a dict.