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How can a diffused(frosted) glass be modelled in path tracing?

Currently I am able to define a window poly line as a clear glass material where it transmits or reflects the ray. I am not clear though how it should work if the sheet of glass is frosted(diffuse transmission?).

enter image description here

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    $\begingroup$ If you know how diffuse reflection works (ie not a specular mirror like reflection), what that does with reflected rays, you do with refracted rays. $\endgroup$ – Alan Wolfe Jun 30 '17 at 4:40
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    $\begingroup$ Keep the same parameters, but increase the roughness. $\endgroup$ – Julien Guertault Jun 30 '17 at 4:48
  • $\begingroup$ Thanks for the comments. it shed light on how I got it wrong first. $\endgroup$ – ali Jul 9 '17 at 9:22
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Assuming that you are familiar with the concept of BSDFs, the usual way of modelling rough dielectric surfaces (i.e. glass, water, plastics) is to use microfacet-based models like Microfacet Models for Refraction through Rough Surfaces.

To make it work efficiently in a path tracer you will need a good sampling strategy, like Importance Sampling Microfacet-Based BSDFs using the Distribution of Visible Normals.

Also keep in mind, that the mentioned BSDF model tends to get darker as you increase roughness because it neglects the light which gets inter-reflected among micro-facets. This can be compensated, but it's not a trivial thing to do.

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