How to get the alpha right when using glass ?

[kiwimage]

yes abstrax, of course I know that you can't render the refractivity of something that isn't there in the 3d scene ! My letters are just here for testing sake. i don't ask for that.
I want to be able to catch an output in wich the object refracts itself, possibly other objects behind, and the environment, but it doesn't make it less transparent.

Refraction + transparency is possible in other renderers.

In Vray :
http://www.workshop.mintviz.com/tutoria ... t-objects/

Look at the glass thickness in the link above: it has refraction, and still a consistent transparency output. If you pay attention to the the edges of glass, the alpha is more opaque, depending on the view angle. It's not solid white alpha AND the material is refractive.
The output for glass alpha is solid white by default, like in Octane right now, but the user has an option tick box available to enable correct transparent output for the material.

That's what we want, even if it needs an extra step in compositing. I wouldn't mind to have 2 outputs : the flat image like today, and the correct alpha.

[mattfrodsham]

This would be a really useful addition if at all possible. +1

[aoktar]

What avoid that you use a mix material for reflaction+opacity?

[kiwimage]

You're suggesting to use a realistic glass and a fake falloff glass and mix them inside of a mix material with falloff as the amount ?

I think it won't work, because the falloff map will tone down the alpha were the refractions are supposed to happen the most.
In the end there'll be none or little refraction.


I'll make a more explicit test scene when I'll have some time ( a glass of water with a straw in it, and a 3d object behind.)

[franchus]

In the Common attributes of the glass you have to check the affect alpha checkbox. And voilá.

[franchus]

Here are the screenshots. Oh, BTW there was already an answer a few posts up, that people decided to not read. A forum is very handy when you read what's posted.

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Settings in the material of C4D:

Settings in Standalone: