Alpha channel through glass material instead of background (Cycles) I'm trying to render some windows, reflecting an environment map, and to be transparent to let light enter inside the house. There are two windows facing each, and I need to see throught both, and keep the alpha channel here.

Here are the window's material nodes that do (half) the trick :



But, as you can see, there is no reflection on windows, which is needed. The "is Camera Ray" is overriding the reflections too. But if I don't add the "is Camera Ray" to the "is Shadow Ray", the background is rendered instead of alpha channel:



So, is there a way to have a "glass" material with both:


reflections of an env map,
light passing through 
alpha channel through


EDIT: Well, the answer from duplicate question suggested doesn't solves the problem. The main difference here is that some parts of the rendered material is viewed over another object (interior walls, here), while some area is over background. The answer from the suggested duplicate does only take account of an object over background only.
By mixing a glass or glossy shader with a transparent shader based on a fresnel node, rays will be allowed straight through the glass at smaller angles of incidence, and will reflect at grazing angles. Rays which go through and reach the environment background will give alpha transparency:



Note that the Fresnel node is not necessary for mixing (setting the factor directly will get something like what you are looking for), but it does make the reflections of the material behave in a more physically based manner.