[Bf-cycles] Alpha pass independent from transparent option

[Antony Riakiotakis]

>
> I understand the risk, but this option is usual in many renders, like Vray.
> The alpha is just an information that can be used in compositions. Some
> times is good to have alpha mask just to saturate a non-trasparent
> background, without the need of complex render layers, for example.
>
> I think it is more intuitive that the alpha slot in render layer always give
> alpha mask, no matter the trasnparent status.
>

It's not a risk, it's incorrect behaviour. In your use case, any alpha
mask will take non-background colours in the result. The colours at
the edges of the background will be incorrect.

Intuitive != correct.
Also, "many others do something" != "it is right"

>
> I believe in freedom :D
>

As opposed to slavery in correctness? Freedom to be lazy is acceptable
I guess. I also get bored when I need to setup render layers. But such
grand proclamations are a bit out of context I think.