Comment 11 for bug 1256702

OK, I just tested locking with the swipe on both phone and tablet. There's no blending anywhere at the moment so I still have to use my imagination.

I imagine you'd only need the greeter fading out, so only the greeter needs some transparency. And more importantly, it looks to me like we'd only have to give the greeter a uniform level of transparency as it fades out. You don't need and shouldn't use an alpha channel to do that. Just let the compositor do it by setting: surface->set_alpha(amount)

The requirement is now even less clear to me than it was before. Now I've seen the animation (without blending) I can't imagine why you'd need an alpha channel to implement the blending/fadeout. The Mir compositor will already happily blend RGBX surfaces via set_alpha().