Light incident on a rough surface will be diffuse after passing it. Angular intensity depends on the grinding of the glass surface.
I'm trying to find information about the scattering indicatrix of light passing through the rough glass: how to calculate it numerically, which parameters are essential, etc., or at least where I should search for it. I would also be glad to find how to calculate it from the equations of electromagnetic fields.
Instead of scattering, think of it as diffuse reflection. The bidirectional reflectance distribution function (BRDF) describes optical surface properties. It's application is as well in computer graphics, as in-depth ray tracing simulations. It depends on angle of incident light $\vec \omega_i$ (2 dimensions) and angle of observation $\vec \omega_r$, also 2 dimensional.
As the OP pointed out, it also depends on the method of surface grinding. If the grinding process is machined with linear strokes, it differs from sliding circular grinding. Finally the BRDF may depend on the spatial coordinates $\vec x$ on the surface.
Its dependance grows with a higher ratio of inhomogenity to laser spot diameter. In total the rough glas surface may depend on 6 dimensions. The BRDF function $$f(\vec \omega_i, \vec \omega_r, \vec x) = \frac{dL( \omega_r, \vec x)}{ dE(\omega_i)}$$ sets reflected light in amount in relation to incoming light. The differential out radiance $L$ and incoming irradiance $E(\omega_i)$ is the description of the rough glas surface.
References to numerical models
