What is a volumetric density field ? Voxes?

This here is similar to jit.gl.isosurf:

https://reference.wolfram.com/language/ref/ContourPlot3D.html

[jit.gl.isosurf] plots a surface along a function f(x,y,z) = const, by using matrix input meaning the function is not known as analytic equation but as values stored in a [jit.matrix 1 float32 xdim ydim zdim]. const is defined by attribute @isolevel

f is a function in 3D space and assigns a value to each position vector (x,y,z). It is called volumetric density field in the help file.

Example with analytic function f(x,y,z) = x^2 + y^2 + z^2.

Let's say we want an isosurface for f(x,y,z) = 9.

x^2 + y^2 + z^2 = 9 or we can also write

x^2 + y^2 + z^2 = 3^2

or better known as a sphere in 3D space with radius 3.

f(x,y,z) = x^2 + y^2 + z^2 is something like the description of a property of 3D space that is isotropic (not dependent on direction) and grows with the square of the distance.

The sphere with radius 3 represents all points in space where this property has value 9.

A more relevant example from physics is

f(x,y,z) = 1 / (x^2 + y^2 + z^2) whose isosurfaces are also spheres.

The property of 3D space described by this equation e.g. is something like gravity 1/r^2 (https://en.wikipedia.org/wiki/Gravity).

For implemenation details see e.g. Marching Cubes

https://en.wikipedia.org/wiki/Isosurface

jit.gl.volume does not draw a surface of constant value but renders f as something that could be described as fog and i think the term volume rendering is associated with this. The density of the fog is described by f.